Categories of Stone
Classification of Stone
Type and Finish
Safety Factors for Calculating Stone
Thickness for Windload and Lateral Anchoring
and Field Measurements
Cleaning and Maintenance
1.1 The following material is intended to provide
basic guide lines for the architect, engineer, stone
contractor, stone fabricator, anchoring device
fabricator, and other interested parties for the
safe and economical use of building stone in
It offers guide lines for the design and application
of building stone using metal gravity anchors and/or
lateral anchors to: (a) clad solid concrete or
masonry, (b) clad the structural frame of a
building, either directly, or to subframes, or to
curtain walls which are attached to the building
It also includes guide lines for the design and
application of paving stones.
2. GEOLOGIC CATEGORIES
OF STONES FREQUENTLY USED IN CONSTRUCTION
2.1 Sedimentary stones (sandstone, limestone,
dolomite) originally formed mainly in sea water, or
lakes, from the remains of animals and plants, also
from transportation and deposition of rock products.
2.2 Metamorphic stones (marble, serpentine, onyx,
slate, quartzite, gneiss) are produced from
sedimentary or igneous rocks by the action of heat
2.3 Igneous stones ( granite, syenite, diorite,
gabbro, andesite and basalt) are formed when magma
(molten rock within the earth) cools.
3. TRADE CLASSIFICATION OF
Society of Testing Materials (ASTM) has issued
standards for the physical requirements of the most
frequently used natural building stones. These
standards are reviewed every five years by their
technical committee, and are subject to revision at
Fine, medium and coarse igneous rock, composed of
quartz, feldspar, and mica with accessory minerals.
Colors range from pinks, reds, grays, blues, greens,
tans, browns, blacks and every color and shade
supplied under ASTM C-615 Standard Specification for
Granite Dimension Stone shall conform to the
physical requirements indicated in the following
A metamorphic recrystallized rock composed of
carbonate minerals (calcite or dolomite) or of
serpentine, capable of taking a polish. The range of
color and texture is wide. For soundness marbles are
classified in 4 groups:
Sound marble with uniform and favorable working
qualities; containing no geological flaws or voids.
Marbles similar in character to the preceding group,
but with less favorable working qualities; may have
natural faults; a limited amount of waxing, sticking
and filling may be required.
Marbles with some variations in working qualities:
geological flaws, voids, veins and lines of
separation are common. It is standard practice to
repair these variations using polyester resin, or
epoxy liners and other forms of reinforcement when
Marbles similar to the preceding group, but
containing a larger proportion of natural faults,
maximum variations in working qualities, and
requiring more of the same methods of finishing.
This group comprises many of the highly colored
marbles prized for their decorative value.
marble contains in excess of 40% magnesium
marble contains not less than 5%, not more than 40%
Travertine marble - a porous or cellularly layered,
partly crystalline calcite of chemical origin.
Serpentine marble (popularly called Verde Antique) a
rock consisting mostly or entirely of serpentine
(hydrated magnesium silicate), green to greenish
black in color, commonly veined with calcite, and
dolomite or magnesite, or both.
marble - translucent, generally layered
cryptocrystalline calcite with colors in pastel
shades, particularly yellow, brown, and green.
under ASTM C503 Standard Specification for Marble
Dimension Stone (Exterior) shall conform to the
physical requirements indicated in the following
Fine to medium grained sedimentary rock having a
minimum of 60% free silica. Colors range from light
grey to yellow and brown. Common commercial
dense, hard, fine grained commonly feldspathic
sandstone of medium to dark greenish grey or
bluish-grey color that may split readily along
original bedding planes to form thin slabs.
dense, medium-grained sedimentary stone, with a
distinctive dark brown to red brown color.
Quartzitic Sandstone which contains at least 90%
- Highly indurated, typically metamorphosed
sandstone containing at least 95% free silica.
supplied under ASTM C-616 Standard Specification for
Quartz-based Dimension Stone shall conform to the
physical requirements indicated in the following
rock predominantly composed of classic sand-sized
grains of calcite, fossils or shell fragments.
limestone: composed largely of spherical particles
limestone: sedimentary carbonate rock consisting
largely of the mineral dolomite.
from light grey, tan to light brown.
supplied under ASTM C-568 Standard Specification for
Limestone Dimension Stone shall conform the physical
requirements indicated in the following table:
Fine grained metamorphic sandstone. Colors range
from shades of blues, grays, greens, buffs and red
with random surface colors of gun-metal, gold and
Fine grained rock which splits easily along its
cleavage. Colors are grey, black, purple, green,
red, and brown.
A foliated metamorphic quartz-feldspar containing
rock characterized by minerals such as mica or
chlorite. Schist splits readily along the planes of
4. NATURAL STONE USES
4.1 Interior use: marble, slate, hard limestone,
quartzite and granite are most often used to build
solid steps, platforms, treads, risers, saddles and
Important considerations for selecting stone for
this type of work are: surface finish, resistance to
wear, slip resistance, resistance to staining, and
maintenance. The use of porous limestones and soft
clayey sandstones is not recommended. High traffic
areas require less porous, harder stones as these
are more resistant to staining and wear.
4.2 Exterior use: bluestone, granite and other
igneous rocks are more appropriate as they are more
durable, resist weathering, and wear well. Abrasion
resistance of stone selected for foot traffic may be
determined with test methods described in ASTM
C-241. Stone may become slippery when wet, therefore
the following finishes are preferred for exterior
use: tooled, flamed, sandblasted or natural cleft.
4.3 For street curbing granite (sometimes bluestone)
is used as it resists weathering and wears well. It
is recommended that the top of street curb be
flamed, or otherwise textured to make the curb more
4.4 Regarding natural stone sills, stools, and
copings see the recommendations described in
paragraph 4.1 and 4.2.
4.5 Open joint pavers may be used on a plaza,
terrace, or on a roof where the designer prefers
cavity under the pavers and where the rainwater or
melted snow can be led along a sloping subsurface to
concealed drain holes. Granite pavers with non-slip
finishes are usually selected for such
4.6 Load-bearing: rubble, ashlar, base, riser,
lintel, arches. For interior use natural stones with
high compressive strengths are preferred. The main
requirements for exterior use are low water
absorption rate, high compressive strength and
flexural strength with resistance to weathering.
4.7 Non-load-bearing: veneer, wall facing, curtain
wall panels, column covers, soffits, wainscots, and
door jambs. For interior use mainly aesthetic
requirements govern. For exterior application low
water absorption rate and high flexural strength
with resistance to weathering are the most important
5.1 Sedimentary stones:
(1) Smooth (machine finished by saw, grinder, or
(2) Machine tooled (uniform grooves).
(3) Chat Sawn (non-uniform, shallow saw marks).
(4) Shot sawn (irregular and uneven markings).
(5) Split face (concave - convex).
(6) Rock face (convex).
(7) Natural cleft.
5.2 Metamorphic stones:
(2) Honed (medium to high honed)
(4) Wheel abraded
(6) Split Face
(7) Rock Face
(8) Natural cleft
Note: Slate and quartzite cannot be polished and may
be sanded, honed or natural cleft. Gneiss will take
all the finishes of marble and may also be flame
5.3 Igneous Stones
(4) Machine tooled (4-cut, 6-cut, chiseled, axed,
(7) Split Face
(8) Rock face
Note: Diorite will not take a good uniform, flamed
platforms and copings are usually installed in
may be of regular or irregular shapes and
dimensions. The thickness of pavers depends on the
type and strength of the stone, on the designed
sizes, and on the nature of the support. Thin tiles
of 12" square or 18" square are mostly used in 3/8"
to 3/4" thickness for interior flooring and are set
either in full cement mortar bed or with a "thin
set" method utilizing a Latex admixture in the
cement mortar, which is spread on the concrete floor
with serrated trowels in an average of 1/8" to 3/16"
thickness. Hairline, or 1/16" wide joints are mostly
used for interior thin-set applications. Exterior
pavers are usually larger than 2' square in size and
their thickness can vary from 1-1/4" to as much as
4" depending on the intended use. As a rule of
thumb, the cement mortar bed should more or less
equal the thickness of the stone paver. No air
pockets should be left under any of the pavers
installed in a cement mortar bed. The use of Lime in
the cement mortar bed is NOT recommended.
Application of any Plaster of Paris for any part of
the exterior flooring will be detrimental. Design of
joint width for exterior pavers may vary from a
minimum of 1/8" to 1/2", using cement mortar, or
caulking. In case of cement mortar, expansion joints
should be introduced approximately every 25 feet.
The use of wire mesh reinforcing in the setting bed,
and a slip sheet under the setting bed, is a matter
of design consideration
Example For "Thinset" Method On Concrete Slab
Interior stone pavers installed on a wood structure
on top of plywood need special treatment because
movement of the wood structure must be anticipated.
To prepare more rigid support, the use of two layers
of plywood is recommended-with the plywood joints
not lined up with one another, but staggered.
Bituminized felt paper and galvanized wire mesh
should be tacked down to the double plywood floor
and not less than a 1-1/2" thick mortar bed should
be prepared using a mixture of 1 bag Portland
Cement, 3 cu. ft. of clean sand, mixed with 3
gallons of Laticrete or approved equal of latex
admixture. Before placing the stone floor tiles on a
wet screed bed, an approximate 1/16" thick latex
based skim coat shall be applied to the back of each
floor tile. Uniform joints of not less than 3/32"
wide shall be maintained. After each piece is laid,
it shall be tapped down using a wooden block to
level the surface and imbed the stone. Care must be
taken not to crack the floor tiles during the
tapping. Joints are filled with Portland cement
with, or without Latex reinforcing, and sealed with
a squeegee. Movement joints shall be applied between
the walls and the floor tiles.
As described in
paragraph 3.2 marbles are classified into 4 groups
for soundness. Group C and D marble tiles are often
reinforced with nylon mesh set in an epoxy (or
polyester resin) film on the back of the tile.
Unless this film is ground off, the cement mortar
bed, or the thinset mortar often separates because
it does not adhere to the epoxy film properly
Example For Mortar Bed Method On Plywood Floor
exterior pavers the use of a sand bed may be
considered. Pavers installed with a sand-set method
can easily be replaced, repaired, or adjusted.
However, the sand-set method shall be used only with
soil conditions that drain well and are stable with
no settling. Proper compaction of a well draining
sub-bed and sand setting bed is critical to prevent
settling and moving. For stability a maximum 1"
thick sand bed should be used with 1/16" wide joints
which are swept with sand. The sand set method is
NOT recommended for interior use.
220.127.116.11 For the
installation of conventional stone paving the
preparation of both the sub-surface and the stone
pavers is equally important.
If the setting
bed between the concrete slab surface and the bottom
side of the stone pavers exceeds 2", concrete fill
should be provided by the General Contractor.
Concrete fill must be properly bonded to the
surfaces to receive stone flooring must be
thoroughly cured, and free from soil, oil, and other
(or concrete fill) shall be saturated with water,
but free water must be removed prior to installation
of mortar mix.
Mortar shall be
prepared using the approved ratio of Portland cement
and clean, damp sand with a minimum amount of water
to produce a workable mass. Mortar must be used
within one hour after mixing, without any additions
A thin coating
of Portland cement grout shall be troweled to the
bed of the stone pavers immediately before each
stone is laid.
Pavers shall be
tapped into final place and made level without any
air pockets left under the pavers and while the
setting mortar is still pliable.
pedestrian traffic on exterior plazas, terraces,
promenades and roofs a pedestal paving system may be
used to obtain a perfectly level walking surface
with open joints, so that the rainwater or melting
snow can drain to the sloping cavity under the
pavers and lead to the drain holes. Presently three
methods are used to provide drainage between the
pavers and the waterproofed structure below.
None of the 3
methods described here provide support for vehicular
operated vehicles, dollies, rolling pipe scaffolds
may be used within the calculated load capacity of
the pedestal paving system.
(1) TREM proof
King Pin Pedestals (by Tremco) have 4 adjustable
stone supports with about 1-1/4" adjustability in
1/16" increments. It can provide a 10,000 lb working
load (2500 lbs per adjustable support) with zero
permanent deformation when supported by a
non-compressible base. To insure uniform joints the
use of 60 to 70 durometer neoprene cross spacers is
recommended at the joint intersections. For
prevention of "moving up" one side of the cross
spacers could be self adhered, or silicon caulking
may be installed above the cross spacers, flush with
the finished stone surface.
(1) Example For Mortar Bed Method On Plywood Floor
System One (by Wausau Tile) is composed of a number
of components such as tabs, shims, pedestals,
reducers, spacers, extenders, etc. Designed to
provide level surfaces above sloping sub-surfaces
the pedestal cavities are filled with specially
blended concrete to provide total and complete
(3) PAVE-EL (by
Envirospec). This pedestal system also elevates the
pavers to provide a drainage plane between the
pavers and the supporting structure below. Pave-El
pedestal is a grid-like structure of high density
polyethylene with integral spacer ribs for either
1/8" wide joints or for 1/4" wide joints. It also
has leveling plates over the pedestal to eliminate
minor deck or paver discrepancies.
(3) PAVE-EL Pedestal System By ENVIROSPEC
Each of the
three types of pedestal methods described above may
be installed directly to the membrane, using
protection boards, or over high density (125 psi)
rigid insulation board.
At larger joints burning cigarette butts may cause
damage to the rigid insulation. Insulation is the
weakest link of the pedestal system, when the
pedestals are installed on rigid insulation.
tiles of 12" square, or 18" square pieces in
thicknesses ranging from 3/8" to 3/4" are often used
for interior cladding set in cement mortar bed on
masonry backup, or set with a "thin-set" method
using a Latex admixture in cement mortar spread on
sheet-rock panels on studs, or set on thin cement
board panels nailed or screwed to the studs.
For "wet" walls
in bathrooms, plastic sheets shall be installed
between the studs and the cement boards. Serrated
trowels will provide an average of 1/ 8" to 3/16"
thickness of thin-set backup to the thin tiles.
Hairline, or 1/16" wide joints shall be used for
natural stone tile cladding for interior
Marbles classified in Group C and D, reinforced with
nylon mesh in an epoxy (or polyester) film on the
back of the marble tile, shall be ground off for
tile application or cement mortar applied to thin
tiles, without the use of mechanical anchors is NOT
recommended for exterior wall cladding. Weathering
resistance and durability of thin tiles exposed to
hostile environment is limited. Freeze and thaw
cycles, water entering into joints and behind the
stone, installation imperfections, and numerous
other hazards are good reasons to avoid exterior
stone-tile without mechanical anchoring and without
well designed weep slots and air ventilation.
stones conventionally anchored to back-up structure
or to masonry.
Anchoring devices are installed to resist lateral
and gravity loads. Anchoring components shall be
designed as simply as possible, with the fewest
components and types to be adjustable, and with
careful prevention of galvanic and chemical
corrosion. Anchors for conventionally installed
natural stone are usually designed to work
laterally, on tension. To resist lateral
compression, mortar spots are placed in the setting
space, usually at the location of the anchors, and
at mid-span between the anchors.
stone veneer ashlar.
Approximately 4"-thick random rectangular shaped
natural stone is often used to achieve a rustic
appearance on exterior cladding. It is recommended
that sufficient air space be left behind the stone
veneer for air circulation, and to provide vent
holes (or vent slots) near the bottom and the top of
the wall. To stabilize such stone veneer, the use of
mechanical anchors is necessary. Corrugated
stainless steel strap anchors are acceptable with
occasional cement mortar spots in the cavity near
the anchors to resist positive lateral loads.
Conventionally anchored thin stone veneer to back up
structure or to masonry.
Cement mortar is used for exterior installations.
Plaster of Paris may be used for interior
application. Stainless steel strap anchors or rod
anchors are used for exterior walls to resist
tensional forces, with cavity between the structure
and the thin stone veneer. Occasional cement mortar
spots are used near the anchors, to resist lateral
loads (compression). Vent holes or vent slots are
provided for exterior installations near the bottom
and the top of the wall. Interior thin stone veneer
is usually installed using brass wire anchors and
Plaster of Paris. No vent holes are used for
interior stone veneer.
Examples For Conventional Laternal Ancoring
Mechanically installed stone veneer.
Stone slabs are anchored, piece by piece, to a metal
grid system which in turn is secured to the
building's structure. Such installations are made
either from scaffolds or from the floor slab.
Miscellaneous steel, such as rectangular tube,
different types and sizes of uni-struts, clip angles
and "Z" shapes may be used to substitute for a
masonry backup. These miscellaneous steel components
are supported by the structural steel and the
anchors are attached to the miscellaneous steel
members. Lateral and vertical adjustability is
accomplished through proper design of the
miscellaneous steel components and/or anchoring
Examples For Mechanical Installation Stone Veneer
to floor panel installation.
Thicker stone slabs are used extending from floor
slab to floor slab, usually without the use of
scaffolds. Stainless steel seat angles are mostly
used for gravity support, with welded tabs on the
horizontal edge to resist lateral forces and
adjustable stainless steel anchors are installed in
the perimeter joints. At locations where some of the
joints are exposed, concealed anchors are installed
to replace perimeter anchors.
Example For Floor To Floor Panel Installation
6 2.2.5 Stone
veneer installed to curtain-wall components.
This is done similar to the glazing method or with
the introduction of special aluminum extrusions for
gravity and lateral supports. Matching kerfs are
provided to receive the extrusions.
Example Of Stone Veneer Installed To Curtain Wall
Stone panels are built in a shop under controlled
conditions. Such systems are sometimes built on to
reinforced precast concrete backing. Such stone
faced precast panels are often designed with
reinforced concrete hunch for gravity and/or lateral
support. A slip sheet is applied in between the
precast concrete and its stone facing to accommodate
differential movement. Stainless steel cross dowels,
or hairpin anchors of different shapes are used to
tie the precast and the natural stone together. A
minimum of one pair of anchor legs is designed for
every 3 square feet. The newest applications have
rubber grommets installed on the anchors at the back
of the stone panels to allow concrete shrinkage and
differential movement, without any damage to the
To pre-assemble lighter panels, stone slabs may be
installed in a plant on metal trusses, or on frames
of different sizes or shapes. Miscellaneous steel,
such as tubes, channel sections, and angles are used
to build the stone supporting frames which must
coordinate the needs of all components to be housed
within the pre-assembled panel such as flashing,
drainage, or insulation.
Example For Granite Faced Precast Panel Installation
Stone, glass, and aluminum components offer cost
effective cladding of high rise buildings.
Stick system. For field-assembled curtain-wall,
aluminum vertical mullions and horizontal components
are extruded, cut to size, pre-punched and
pre-drilled for connections and weep holes. Properly
numbered they are then shipped loose for job site
erection. Glass and stone are used as glazed panels.
Silicone sealant is used for watertight sealing and
carefully designed bites and aluminum pockets are
used to accommodate anticipated building movements
and to prevent air and water infiltration.
(1) Example Of Preassembled Stone System On Metal
curtain-wall systems may have glass and stone
shop-installed into prefabricated frames. The size
of the designed units is governed by shipping
limitations and field conditions. Stone slabs of a
minimum 1-1/4" thickness are either set in pockets
similar to glass or are kerfed for mechanical
anchoring. Extreme care is required to move,
transport and field-erect unitized curtain-walls.
(2) Example Of Shop Assembled "Utilized"
conditions shall be examined, if possible, before
installation starts. An experienced foreman or
supervisor shall lay out the necessary lines and
grades from the engineering marks provided by the
anchoring devices, other materials and equipment
shall be organized and lined up by the time
shipping, unloading, and distribution shall be
carefully planned so that sufficient stone arrives
at the job-site in logical setting sequence. Stone
should be stored reasonably close to the setting
place, to insure trouble-free continuous
Installation shall be in strict accordance with
specifications and approved shop drawings. Safety
regulations shall be strictly observed.
chain hoists, scaffolds, etc. shall be inspected
and, if necessary, reconditioned for safe and
effective use on the job.
Scaffolds generally used for stone cladding may be
classified into four types:
(2) Suspended scaffold for material handing
(3) Suspended swinging scaffold
(4) Bosun's chair
Scaffolding is normally used for stone installation
of limited height. It can be used above 30 feet in
height, but must be tied back to the structure.
Scaffold designed for material handling is normally
used by brick masons for installing brick and block
walls on high-rise buildings. Occasionally, they are
also used for installation of stone cladding, where
cladding units and materials must be stored on the
are usually 5-feet wide and are suspended at four
points from steel wire rope.
swinging scaffolds are suspended only at two points,
from steel wire rope, and are not designed for
material handling. Swinging scaffolds have a better
efficiency rating because one can raise or lower
them with greater ease and in less time. Commonly
used lengths are from 12' to 24' at 2-foot
intervals. Stirrups are 28" wide. A safety line is
required for each person riding a swinging scaffold.
Chair is normally used for minor repairs or limited
stone installation. The operator has little control
keeping the chair in a working position. It is NOT
recommended for use if wind is over 5 m.p.h.
When using any
type of scaffold, the safety rules and
manufacturer's instructions shall be strictly
and supervision are the keys to successful
installation. Clear, readable, logically numbered,
and detailed shop drawings are essential.
shall give all necessary information to fabricate
and install all stone requirements and should also
indicate tolerances with all materials and
components fully identified.
RECOMMENDED TEST METHODS
AAMA 501.1 Test
for Water Penetration using dynamic pressure.
ASTM E-283 Air
Infiltration Test by static pressure.
Structural Load Test by uniform static pressure
(positive and negative).
Water Infiltration Test by static pressure.
The four test
methods listed above are used in the stone industry
to test the performance of stone panels installed on
a grid system, a strut system, or stone panels
assembled on pre-fabricated steel frames, or
trusses, or used as components of field-installed
curtain-wall or shop-assembled unitized
ASTM C-97 Water
Absorption Test is recommended for all dimension
stones used for exterior installation and for
interior flooring and base course. Maximum
absorption rate by weight for granite is 0.4%, for
marble 0.2% and for medium density limestones 7.5%.
Modulus of Rupture Test is helpful in the design of
panel sizes, thickness, and surface finish and is
useful to design limitations of anchoring. Minimum
requirements of modulus of rupture for granite 1500
psi (10. MPa); for marble 1,000 psi (7 MPa) and for
medium density limestones 500 psi (3.4 MPa).
Compressive Strength Tests are adequate to design
simple construction, but not sufficient for thin
veneer design for high rise construction. Minimum
requirements for compressive strength: for granite
19,000psi (131 MPa), for marble 7,500 psi (52 MPa),
and for medium density limestone 4,000 psi (28 MPa).
ASTM C-215 is
used as a non-destructive test for detecting
significant changes in the dynamic modulus of
elasticity of the test specimens due to cycling, by
measuring their transverse frequencies after
predetermined group of cycles.
research and experience, it is presumed that the
total loss of strength of natural stone cladding
will be in the 40 to 50% range, due to weathering,
over the life of a building.
is also affected by the methods used for finishing
its exposed surface. Polished granite appears to be
the most resistant to hostile attacks of the weather
and to aging. Some fine grained white marbles lose
the greatest amount of strength. Limestone falls in
between granite and marble.
Abrasion Resistance Test determines the abrasion
resistance of all types of natural stone for floors,
steps, and similar uses where wear is caused by the
abrasion of foot traffic. The minimum abrasion
resistance (Ha value) of granite is 25. The minimum
abrasion resistance value of both limestone and
marble is 10.
Flexural Strength Test provides better information
for the design of panel sizes and thickness, surface
finish and anchoring limitations. Minimum
requirements for flexural strength of limestone have
not yet been established by ASTM Committee C-18. The
minimum requirement for granite dimension stone is
1200 psi (8.3 MPa) and 1000 psi (7MPa) for marble.
FLexural Strenght Test
TEST This test is used for all engineered systems
having thin veneer dimension stone for exterior
cladding. The method of anchor pull-out tests and
minimum requirements are engineered and calculated
by the design engineer of the anchoring system
Anchor Pull-Out Test
These tests are done for large jobs to control the
performance of stone panels produced with stone
blocks from various quarry locations and to test the
performance of the anchor connections as described
by ASTM C-1201. Chamber tests can be performed in
the fabrication shop from randomly selected blocks,
or at the job site by building a small wood chamber
around the designated stone slab and pumping air out
of the chamber to create a suction force generally
1.5 times the design load. Such tests can also be
made until failure occurs in the stone slab, or its
anchor provisions. It is desirable that no failure
take place until 4 times the design load is reached.
There is no standard test procedure for the
durability of natural stone. Until standard test
procedures are developed, ASTM C-666 which describes
the resistance of concrete to rapid freezing and
thawing is often used with minor modifications (to
be reasonably analogous to the conditions the stone
will experience on the building) to test the
durability and aging resistance of dimension stone
on an accelerated basis. If such tests take 300
cycles, then it will require close to three months
to perform. They are generally costly.
A control group of specimens is tested vs the cycled
specimens. Increase in absorption of the specimens
after cycling, weight loss, decrease of strength in
compressive strength in modulus of rupture and in
flexural strength shall be evaluated and any visual
deterioration or erosion during the test should be
recorded and reported including the number of cycles
at which such defects were noted.
ratio of the modulus of rupture of a thin section of
natural building stone could also give an
approximate evaluation of the durability of the
rock. Erhard Winkler in his paper "Durability Index
For Stone" (1985), prepared for the International
Conference on Deterioration and Conservation of
Stone, gives the relationship of the general stone
evaluation as function of dry-to-wet strength ratio
based on the modulus of rupture.
E. Winkler Wet
& Dry Ratio Durability Index
PULL-OUT TESTS of anchoring of stone facing to
precast panels. Such tests are made to establish the
resistance of the natural stone to separation from
SELECTION OF STONE TYPE AND FINISH
8.1 Quarry assessment. Prior to selection of the
stone, it is advisable to obtain reliable
information to determine if the quantity and the
largest stone sizes required are readily available
from the quarry source. Rates of block production on
seasonal basis shall be evaluated. The uniformity of
the color, texture, and physical properties of the
rock must be checked as well. It is also advisable
to establish a mutually acceptable range of color
and texture to prevent possible later
dissatisfaction or dispute.
8.2 Manufacturing plant assessment. Past and current
performance on similar projects shall be evaluated.
Fabrication capacity within the required time frame
shall be examined. Crating and transportation
facilities should also be examined. Quality control
during fabrication must be insured.
8.3 In addition to aesthetic considerations, the
selected stone has to resist possible present and
future environmental attacks during the planned life
span of the building. Exposure to weather may cause
changes in shade or coloration. Polluted air, acidic
and sulfuric rainwater may cause changes in
appearance. Serious and repeated environmental
attacks, combined with freeze-thaw action may cause
spalling and slow deterioration if the improper type
of stone and/or finish is selected.
8.3.1 Failure investigations and research work do
not justify the use of thin marble veneer for
exterior cladding high-rise buildings in an
environment where air pollutants, carbon dioxide
(C02) or sulfur dioxide (S02) are present.
Atmospheric water dissolves these gasses creating
"acid rain" which, in turn, can cause degradation of
the marble veneer.
8.3.2 Freeze and thaw cycles can also change the
original characteristics of the thin marble veneer.
Due to thermal expansion or contraction, and
moisture, some of the thin (1" to 1-1/2", or 2.54 to
3.81cm) crystalline marble slabs will release their
stress of geological origin and when cooling off or
warming up, will not fully return to their original
content of natural cementation in the marble and the
size of the crystals may play important roles in the
moisture activated bowing of the thin marble veneer.
8.3.3 Warping is also caused by unequal moisture
absorption which happens when one side of the slab
stays dry while the other side becomes wet. This
type of warping can be prevented by providing
adequate ventilation, using weep slots (weep holes)
to keep the cavity, behind the marble veneer, dry.
8.4 In selecting panel sizes, consideration must be
given to the capability of the quarry and the
fabricating plant to economically produce the
selected sizes and thicknesses.
thickness shall be proportionally adequate for the
panel size, anchoring system and the finish, without
losing sight of economic considerations. Where wind
loading criteria is established by the
specification, the selected thickness as well as
selected anchoring system shall be substantiated
with calculations by a licensed Professional
Engineer. Tests shall be conducted by an independent
8.4.1 Thermal (flamed) finish will effect the
strength and durability of thin granite veneer.
Flame treatment of granite will produce a type of
finish which is desirable to many architects and
building owners. However, it will reduce the
effective thickness of the thin granite slab,
together with its bending strength. This may become
critical for the long term durability of the thin
Freeze and thaw
cycles of flame-treated thin granite may alter the
always present micro-cracks to macro-cracks*, making
it more vulnerable to further deterioration,
permitting absorption of water to a depth of about
1/4" which may freeze within the flamed thin granite
*MICRO FRACTURES were formed when the molten rock
(magma) came to the surface of the earth and it
cooled off. Micro fractures can not be seen by the
*MACRO FRACTURES have very limited depth and width,
however they are visible with the naked eye. Macro
fractures do not impair the structural integrity of
the intended use of the rock.
8.4.2 Functionally, a polished finish is the most
desirable finish of thin granite veneer used for
exterior cladding. Polishing procedures close the
pores of the thin stone slab, protecting its surface
from deterioration caused by hostile environmental
8.4.3 Polished granite and marble are recommended
for interior vertical walls.
For interior flooring, polished granite is
preferred, but good quality polished marble is often
used. The use of flamed, honed, sawn or sandblasted
oolitic or dolomitic limestone for wet room flooring
such as baths or showers is NOT recommended.
It is NOT desirable to combine granite and marble
for a floor pattern due to the difference in
abrasion rate. If repolishing is needed, it will be
difficult to handle with mixed materials.
In the selection of marble flooring material for
high traffic areas, the quality of the marble pavers
and their resistance to heavy foot traffic should be
carefully considered. Stratified marble or
conglomerates are often contaminated with clay,
sand, and other such minerals, which after being
subject to foot traffic and maintenance procedures,
may become fissures on the finished surface.
*FISSURES are narrow openings in the rock, having
occasionally more depth than width. Fissures are
very common in travertine marble and are caused by
9.1 Where specifications and contract drawings
describe an engineered system of stone cladding, it
is recommended that the Engineer of Record be
(1) Maximum expected deformation and movement of the
(2) Safe and economical suspension system.
In case of performance specification, the design
criteria shall be established by the Engineer.
9.2 Stone panel suspension design shall be based on
design criteria established by the specifications
and applicable building codes. In addition, the
architect, engineer and stone contractor
(fabricator) shall take into consideration all other
factors for a properly designed and functional stone
suspension system such as:
(a) Expected windload.
(b) All building movements-sway, elastic deformation
and creep, shrinkage of structure and"47or
supporting back-up walls, thermal movements of
structure and/or cladding.
(c) Connection design to accommodate combination of
building movements, fabrication, erection tolerances
and economy of erection.
(d) Dangers of freeze-thaw action.
(e) Prevention of corrosion of anchoring devices.
(f) Joint design.
(g) Possibility of water penetration.
(h) Ventilation requirements behind stone panels.
(i) Transportation and handling requirements.
(j) Coordination with requirements of adjoining
(k) Testing program.
9.3 Reinforced concrete buildings may have
dimensional changes or a combination of dimensional
changes due to the following:
(1) Shrinkage of concrete structure.
(2) Elastic deformation and creep of concrete
under sustained load.
(3) Thermal movements.
(4) Sway (of tall buildings).
9.3.1 Drying shrinkage of cast-in-place concrete is
perhaps the most important factor to be considered
by the designer of the stone suspension system.
Drying shrinkage is dependent upon many factors,
such as the cement, aggregate, and water content of
the concrete mixture, together with ambient
temperature, humidity, etc. Certain aggregates may
have very high shrinkage characteristics.
Under normal conditions, one can assume that
cast-in-place concrete will shrink as follows:
During the first 2 weeks-approximately 33% of the
During the first month-approximately 45% of the
During the first 3 months-approximately 66% of the
During the first year-approximately 90% of the total
The complete drying and shrinkage may take several
years. However, since the major part of the
shrinkage takes place within the first 3 months it
is advisable, when possible, to start stone
installation after the poured-in-place concrete
structure is complete.
The average drying shrinkage value for
non-reinforced concrete is in the range of 0.0005 to
0.0009 x length. Reinforced concrete may be
calculated to half of that.
9.3.2 Creep of concrete under sustained load will
cause permanent deformation, which is also a factor
to be considered during the design stage.
9.3.3 Thermal movement of a poured-in-place
reinforced concrete structure using normal stone
aggregate is relatively low: 0.0006% per 100° F.
In calculating thermal movement of a stone clad
concrete structure one can use a maximum of 70° F.
9.4 Tall steel-framed structures may also have
dimensional changes or combinations of dimensional
changes caused by the following:
(1) Thermal movement.
(2) Elastic deformation under sustained load.
9.4.1 Thermal movement of steel framing can be
expected: 0.0007% per 100° F. In calculating thermal
movement of a stone clad fire-proofed steel
structure one can use a maximum of 70° F.
9.4.2 Elastic deformation of high-rise steel framed
buildings should be taken into consideration.
9.4.3 If cladding is supported on the edge of the
slab, or concrete beam, long term deflection should
9.5 Cladding may have dimensional changes caused by
temperature. Cladding usually has substantially
greater temperature changes than the protected
concrete or steel structure of the building. In
North America, one can expect temperature changes in
the cladding as high as 170° F. depending on its
color and texture.
9.6 Provide expansion joints to accommodate building
and cladding movements. Make sure that joints under
gravity supports are kept free from any debris,
shims, etc. to avoid "stacking" of stone panels.
10.1 All stone
cladding panels anchored to a building are subject
load (the weight of the stone panel).
load (wind load, structural and thermal movement,
seismic movement). The location, shape, and size of
all anchors must be designed and calculated to
safely support the stone for all stresses to which
they may be subjected (compression, tension,
bending, torsion). Inducing excessive stresses in
the stone must be avoided.
Loadbearing (gravity) anchors are recommended, if
possible, to support stone cladding panels, under
(or close to) the bottom bed.
Example For Combination Of Gravity And Laternal Load
In case of
exposed heads above windows or in similar conditions
where exposed gravity anchors are not allowed under
the bottom bed of the stone panels, it is customary
to use epoxied and doweled stone liners for interior
applications, stainless steel concealed supports
should be designed. Epoxied liners for exterior use
should be avoided.
Example For Concealed Support
liners or other epoxied stone components for
exterior use can not be avoided, then the following
shall be carefully considered:
surfaces of the stone components to be epoxied
together clean and dry
specified epoxy and follow manufacturers
recommendations . use clamps until epoxy is
corrosive mechanical connections (dowels) where
possible, in addition to the application of
epoxy, to prevent separation in case of improper
workmanship, or failure of the epoxy.
For 2-12" thick
or thicker cladding panels, the use of clip angles,
or plates, placed in non-continuous slots, cut in
the back of stone panels is recommended. The veneer
may be supported by properly designed stainless
steel plug anchors drilled in the sides and engaged
with stainless steel threaded rods supporting
stainless steel clip angles. If plug anchors cannot
be used because the sides are exposed, then the use
of properly designed stainless threaded bent rods
(often called "J" anchors) set in epoxy fill, in
back of thin stone veneer is also an acceptable
practice. Stainless steel threaded bolt (called Cold
Springs #31 anchor) seated in a matching routed slot
in the back of the stone veneer also provides an
excellent concealed anchor, when the stainless steel
threaded bolt is attached to a stainless steel (or
aluminum) clip angle, which could serve as a gravity
and lateral supporting member.
recommended that when using a metal clip angle in
the back of the stone engaged to a plug anchor, or
to a "J" anchor, or to a #31 anchor, a "stressless"
stainless steel or aluminum disc with a threaded
hole should be screwed on hand-tight, with epoxy
film facing the back of the stone slab, so that when
the metal clip angle (or other device) is attached,
it is tightened against the metal disc and not
against the stone slab, preventing inducement of
stress into the stone.
10.3 Lateral anchors are recommended in the joints,
between the cladding panels. For conventionally
installed stones lateral anchors are usually round
anchors, or pins fitted into drilled holes, or strap
anchors fitted into anchor slots in the edges of the
stone. Sometimes it becomes necessary to provide
concealed lateral anchors into the back of the stone
which is connected and adjusted at the back of the
stone panel. It is difficult to provide "blind"
(concealed) anchors into solid masonry and, if
possible, should be avoided. Some anchors may be
designed as lateral and gravity anchors, such as
plug anchors, "J" anchors, or #31 anchors.
customized anchoring is described under
"Pre-assembled Systems" and "Curtain wall
The number and distribution of the anchors should be
determined by calculations and by the applicable
code. Calculations shall be based on the forces to
which the cladding will be subjected.
fabrication technology makes possible the production
of thin (1/4" to 1/2") stone veneer, which is
installed using a "thin-set" method for interior
use. Very thin stone, epoxied or honeycomb-backed,
is also marketed, mainly where the weight of the
panels must be limited. None of these very thin
stones should be used for exterior installations,
because of their very limited resistance to aging
and weathering. Based on today's knowledge of the
state-of-the-art, it is recommend that all stone
panels for exterior installations be mechanically
10.4 Anchoring design should be sufficiently
adjustable to overcome expected tolerances in
building construction and to overcome the tolerances
in natural stone fabrication, or a combination of
both. To avoid use of anchors at improper locations,
it is recommended that anchors with similar
functions be designed to resist forces at any
location of the building.
panels and anchors shall be designed to resist
positive and negative windloads. The height of the
building, the velocity of expected wind gusts, and
the topography of the surrounding area will
determine the windload criteria. For information and
guidance in design of structures to resist windloads,
see: WINDLOADS ON BUILDINGS AND STRUCTURES NBS BSS
30 issued by the U.S. Department of Commerce
National Bureau of Standards, and MINIMUM DESIGN
LOADS IN BUILDINGS AND OTHER STRUCTURES - A 58.1
issued by the American National Standards Institute.
10.5 The shape, size and location of gravity and
lateral anchors, as well as their attachment to the
structure, shall be carefully designed and
calculated for all mechanical stresses to which they
could be subjected: compression, tension, shear,
bending, and torsion. Special attention is
recommended in the design of horizontal joints under
the gravity angles to avoid load transfer to the
The use of
round holes in stone to receive anchors or dowels is
preferable to the use of slotted holes (kerfs) to
receive strap anchors, since stones with the same
thickness, using round anchor holes, usually resist
mechanical stresses better than stones with slots.
anchors are preferable to "split-tail" anchors. When
using "split-tail" anchors or "drop dowels" to
connect two stone panels, it is recommended that the
anchor or dowel cavity on one side in the first
stone panel be grouted and the anchor or dowel
cavity on the other side in the second stone panel
be caulked with fast curing silicone or high modulus
10.6 All metals in direct contact with stone should
resist corrosion and be non-staining. Anchors not in
direct contact with stone may be hot dipped
galvanized for exterior work, electro-galvanized, or
properly painted for interior work. Above all, care
shall be taken to avoid galvanic corrosion using
non-compatible metals together without a proper
corrosion occurs when a more noble metal in contact
with another metal in the presence of moisture, will
impair the strength, or will gradually deteriorate
the less noble one. The ratio between the mass of
the two dissimilar metals, the area of their
contact, and the difference in their voltage
potential will determine the degree of corrosion and
10.7 For exterior gravity and lateral anchors in
direct contact with stone cladding the use of 302 or
304-type stainless steel is recommended. Hot dipped
galvanized carbon steel gravity anchors have a heavy
zinc coating which will prevent corrosion for many
years. Drilled holes, or rethreaded holes are a
potential source of corrosion. Electro-galvanizing
does not provide reliable protection for exterior
anchoring. Electro-galvanized anchors are liable to
scratch and rust. The use of galvanized anchors in
direct contact with limestone is NOT recommended.
Brass wire is widely used for interior natural stone
Plaster of Paris, or Gypsum, has little resistance
to water penetration and is considered unsuitable
for use in exterior walls.
TABLE NO. 1
10.8 Table No.
1 indicates recommendations for bi-metallic contacts
for the most frequently used metals in natural stone
welding shall conform to the provision of the code
for welding contained in "Building Construction of
the American Welding Society."
RECOMMENDED SAFETY FACTORS FOR CALCULATING STONE
SLAB THICKNESS FOR WINDLOAD AND FOR LATERAL
ANCHORING IN STONE.
11.1 Due to the tolerances allowed for erecting
steel structures and pouring concrete, and due to
other field conditions, the setting space behind the
stone panel may have large variations and other
discrepancies such as misplaced or left-out inserts,
Based on this,
it is recommended that the design of all anchoring
devices be for the worst possible condition and to
follow A.I.S.C. specifications for allowable
11.2 When testing natural stones, test results in a
close range indicate a stone with more consistent
physical properties, while test results in a wider
range show the weaker and stronger areas in that
A wide margin of safety is needed not only to meet
the varying strength of the building stones, but
also to provide for possible deterioration in
strength of the stone after it is placed in the wall
due to environmental attacks and normal expansion
and contraction, freeze-thaw cycles, or other
external forces, and aging.
Since the basic chemical and physical
characteristics of natural building stone are
determining factors of its strength and durability,
it is recommended that when calculating slab
thickness for wind load, for handling and for
lateral anchoring, different safety factors be used
for the sedimentary, metamorphic, and igneous origin
rocks, so that the safety factor will reflect not
only the range of spread in the test results but
will also agree with the general chemical and
physical characteristics of the rock.
Using a minimum of five (5) test specimens,
preferably from different blocks and slabs, it is
recommended that the spread in these test results be
converted into safety factors as described in Table
recommended that, when possible, the full scale
anchoring system be laboratory tested in lieu of
relying solely on calculations. Based on a minimum
of five (5) pull-out test results for anchoring
stone, one can use the same safety factors which are
shown in Table No. 2 for calculating the stone
thickness for windload.
As a general rule, natural building stones possess
higher strength in the direction at a right angle to
the bedding plane than to any other direction.
Therefore, it is recommended that when testing
natural building stone to establish safety factors,
the tests should be performed on specimens which are
fabricated for testing at parallel direction with
the bedding plane.
specifications shall specify, and inspection shall
control, the fact that all stone blocks are slabbed
at the parallel direction with the bedding plane.
building stone is used as load bearing material, a
100% increase to the safety factors is recommended
as shown in Table No. 2 for stone thickness.
mentioned safety factor recommendation is reasonably
conservative. It is written as a guide to users in
the stone industry for the avoidance of potential
failure and litigation. The factor of safety depends
upon the Building Code and the judgment of the
and chemical characteristics of the stone determine
its durability, resistance to moisture and
atmospheric pollutants (after it is placed in the
wall). Consequently, it is not advisable to use the
same safety factors for rocks of igneous,
metamorphic, and sedimentary origin.
and chemical characteristics of the rock also vary
widely within these three groups. Nevertheless, such
a simplified grouping will provide some degree of
guidance to engineers, architects and designers who
are calculating stone thickness for wind and
anchoring, but are not thoroughly familiar with all
its physical and chemical characteristics.
The basic chemical and physical properties of
natural building stone vary according to its
geological origin. These characteristics determine:
• elastic properties, compressive and flexural
• hardness and resistance to erosion
• resistance to attacks of acidic solutions
• resistance to attacks of freeze/thaw cycles
• internal structure, coherence of the minerals
In addition to the wide variation of the weak and
the strong zones of the natural building stone,
there is an endless list of occasions when damages
have caused substantial weakening in some of the
installed stone panels, and the stone has become
substantially weaker than the previously received
test results would indicate.
It is common
knowledge that most of the failures occur at, or
near, the anchors. Unless properly conducted anchor
pull-out tests suggest differently, it is reasonable
to use more conservative safety factors when
calculating stone thickness for anchoring, than for
calculating stone thickness for wind. Of course the
flexural and shear strength of the homogeneous metal
anchors may be safely calculated regardless of the
origin of the loads. However, natural stone is
heterogeneous, therefore weak zones at, or close to,
the anchors could lead to failure much before the
life expectancy of the rock.
The specification, design and detail of joints and
sealants should be done by qualified persons.
12.1 Loadbearing joints in vertical walls transmit
loads to the stone below. Shims are used to provide
the designed joint width until the cement mortar
cures. Cement mortar is also used for pointing or
grouting horizontal surfaces such as paving, steps,
and copings, etc.
12.2 Sealants applied in joints of vertical walls
accommodate movements of the stone cladding and
movements of the structure which may be transmitted
to the cladding. Sealants need back-up materials
which compress easily and do not bond to the
sealant. Most sealants require primers for good
adhesion. Particular care is necessary to have clean
joints to insure proper adhesion.
12.3 Expansion joints with sealants are designed to
accommodate vertical, as well as horizontal,
building movements. Expansion joints are needed in
stone joints beneath supporting steel angles to
prevent stress concentrations due to differential
vertical movements between the stone veneer and the
building structure, or due to deflection of the
spandrel beam, thermal movement or sway. Utmost care
is needed to make sure that shims, or any other
rigid objects, are not left in the expansion joints.
Vertical expansion joints shall be designed to
accommodate thermally or otherwise induced
horizontal movements of the stone veneer or its
Adequate expansion joints are needed on roof
parapets which are open to the weather on two sides,
to roof copings, and to expansion joints between
intersections of a stone base course and a
horizontal sidewalk where lack of properly designed
and executed expansion joints may cause serious
joint widths the fabrication and installation
tolerances shall be considered. For prefabricated
panels such as stone faced precast or stone on
trusses, unitized curtain wall panels, joints
between the stone slabs should be caulked in the
shop under controlled conditions. Only the joints
between the prefabricated units should be caulked at
the jobsite and using the same caulking compound
which was used in the shop. When designing joints
the potential problems due to handling, loading,
transportation, unloading and erection should also
be carefully considered.
should be designed realistically. Aesthetic
considerations should not be more important than the
functional requirements. Designing joints too small,
could create serious functional problems.
12.4 Sealants are classified as single component or
Single component sealants have a slower curing time.
Non-sag type sealants are applied with a gun.
Self-leveling type sealants are poured into paving
joints and do not require tooling.
fast and resists ultraviolet light. Urethanes show
good resistance to abrasion and are preferred for
use in paving joints. To avoid smears in critical
areas masking tape may be used along the joint
Part of the jointing design is the selection of the
proper joint filler which controls the depth of the
sealant in the joint and can also act as a secondary
barrier in case of sealant failure.
joint fillers are non-absorbent. If the ambient
temperature is very high, some closed cell joint
fillers may cause bubbling of the sealant.
Puncturing or over-compression may also lead to
bubbling of the sealant.
Open cell, sponge type joint fillers have water
absorption characteristics. Kerfs, or holes in the
tops of stones must be filled with a high quality
application shall be according to manufacturer's
recommendation, and prior to the expiration of shelf
life of the sealant. If stone thickness and setting
conditions allow, the use of double sealing (back
and front) is recommended.
usually extruded or pre-formed for joints where
pressure will compress the gasket for efficient
12.5 Water leakage may lead to such serious problems
as damaging the anchoring system. Due to the effects
of freeze-and-thaw cycles, water trapped in anchor
slots may crack the stone and cause failure of the
exterior stone joints must be designed and properly
sealed to prevent leakage.
After the support structure and stone slab
supporting system is reviewed, the stone joints
should be examined.
The taller the building, the more flexural
deflection, shrinkage, and creep or thermal movement
of the structure may be expected.
joints between the cladding units, it is important
to take into consideration the expected dimensional
changes in the parts of the building to which the
stone cladding is applied. The larger the stone
slabs the more stress is put on the small stone
joints by the mechanical and thermal movements of
the structure. However, reducing the stone panel
size will increase the number of joints.
Potentially, more joints also mean the greater
possibility of human error and imperfection in
installation, as well as more erosion of joint
sealants due to exposure to the elements.
12.6 Applications shall comply with the
specifications, with design details, and with the
sealant manufacturer's recommendation. The most
common problem during the application is the change
in the joint sizes, due to tolerances of stone
dimension. Such field conditions may result in
undesirable deviations from the jointing design and
may lead to leakage and failure. Therefore, before
sealant application begins, qualified persons should
inspect joint conditions and either remedy improper
joints, or re-design the joint treatment.
CONTROLLING WATER PENETRATION
Flashing. No cladding is perfectly waterproof. Wind
driven rain will find its way behind stone panels
where pointed cement mortar or caulking separates
the stones. Porosity, which is the volume of voids
related to the apparent volume of the stone, under
pressure of wind driven rain could let water seep
through. Condensation can also produce moisture on
the back side of the stone panels. Therefore, a
second line of defense is necessary to collect and
let the water out of the cavity behind the stone
panel, and ventilate the cavity to keep the stone
and the back-up masonry dry. Properly designed weep
holes, weep slots, and flashing serve this purpose.
Flashing is a flexible material installed at one
end, higher up against the structure, and turned at
the other end, into the stone joint. Waterproof,
rubberized fabric, polyethylene, or soft neoprene
sheets, or soft thin-gauge stainless steel flashings
are the most widely used.
qualified person, with a thorough understanding of
the cladding system, including the windows, is
needed to design the flashing and the components of
the secondary water defense. Leaving it only to the
person installing the flashing is NOT recommended.
Prefabricated systems, such as stone on trusses, or
stone on unitized curtainwall panels require a
galvanized sheet metal water defense designed behind
the stone slabs, including gutters and weep-tubes to
collect and discharge water from the cavity
(see Fig. 13).
QUARRYING AND FABRICATION
14.1 For large
projects it is prudent for members of the design
team to visit the quarry and the manufacturing plant
to check on the availability of the stone required.
To obtain a more uniform and aesthetic appearance,
as well as more uniform strength, all blocks should
be quarried to dimensions which will allow uniform
slabbing in relation to the bedding plane of the
rock. Most stones have higher flexural strength if
slabbed parallel with the bed. Sedimentary rocks,
such as limestone and sandstone, should always be
slabbed parallel with the bed.
Fabrication shall be in strict accordance with
specifications and approved shop drawings.
Tolerances described in the specifications must be
followed. Shop inspection of fabricating is strongly
recommended to protect all parties from possible
later disputes about color ranges, marking,
structural defects, or improper thickness. Anchor
holes, cut outs for other trades, and lifting holes
shall be provided in the shop and NOT on the job
projects a mock-up sample wall should be erected in
the fabrication plant as a guide to control the
uniformity of the stone color and texture. If this
is not done, stone slabs with improper coloration or
texture may be cut to final dimensions and shipped
to the job site where they may be installed. At this
point, the removal of rejected pieces and
re-installation can be very costly.
To prevent the
installation of slabs with improper quality,
coloration, or texture a mock-up sample wall, or
floor, should be erected at the jobsite, for the
approval of the Architect. Once the quality and the
appearance of the stone and its method of
installation is approved, it is critical that proper
supervision be maintained to insure against
sub-standard installation, or against the use of
stone slabs beyond the approved range of color,
texture, and quality of the mockup.
the consistent quality of the stone, it is prudent
to apply specially designed shop tests for a certain
percentage of the slabs to be used on the project.
Such shop testing is usually done by applying
uniformly loaded weight on the slabs, or by using a
small test chamber for applying static pressure.
(see paragraph 7 - Chamber Tests).
composite panels, such as precast concrete faced
with natural stone, or stone slabs pre-assembled on
steel frames or trusses, inspection of the assembly
is recommended to insure the specifications and
design details are followed. In many cases the
anchors, shelf angles, reinforcing steel,
insulation, slip-sheet and other components are not
exposed to view. The consequences of improper
assembly may only become evident years after the
shall be taken in handling and storing composite
panels to prevent bowing, chipping freeze-thaw, and
HANDLING, STORING AND TRANSPORTATION
15.1 Special care is needed in handling and storing
stone slabs to prevent bowing, cracking, chipping,
and staining. Supports shall be designed to avoid
over-stressing or cracking of stone panels during
storage and transportation. Stress concentration due
to improper handling may interconnect micro or macro
fractures of geological origin which may be present
in the stone slabs. Moisture and thermal cycles may
cause later distress and failure of such panels on
the building facade.
should be properly palletized or crated on edge for
safe transportation and for economic unloading and
distribution. Non-containerized crates should be
marked "fragile" and packed and handled with
increased care due to the higher breakage hazard.
crates, or pre-assembled panelized stones on trucks
or in containers shall be carefully secured to
prevent them from shifting. Pre-assembled panels for
storing and shipping shall be designed so that the
frame supports the stone and no load is transmitted
through the connections to the stone slabs.
slabs or pre-assembled panels are erected directly
from the truck or trailer, ample room will be needed
at the job site to distribute them reasonably close
to where they will be installed. They should be
distributed so their identification numbers are
visible. Double handling, moving stone at the
jobsite, will greatly increase the possibility of
breakage or chipping.
trucks or containers at the job site should also be
done carefully. If a "cherry picker" or a mobile
crane is used for unloading, a permit is usually
required. Forklifts or monorails are also often used
to unload trucks or container shipments.
The method of
storing stone on structural floors should also be
carefully planned. Unpolished slabs, in particular,
should be protected from staining. The storage areas
should be adequate, accessible, and the moving of
materials of other trades should be limited.
Pre-loading floors should be in accordance with
requirements set forth by the engineer of record.
slabs are stacked, they should be separated with two
non-staining skids placed approximately one-quarter
of the way from each end of the slab. Skids should
be placed directly above one another to prevent
cracking or breakage.
Pre-assembly of stone on steel frames, curtainwall
components or precast concrete is done in a shop
under controlled conditions. If possible,
pre-assembled panels should be shipped in a position
similar to the one in which they will be installed.
For supporting seats, the use of special hard rubber
pads is recommended. It is prudent to protect the
stone from possible staining during transportation.
15.3 All cladding stone above the first course shall
have lifting holes. Type and location of lifting
holes shall be carefully designed for safety and
clearly defined on the shop drawings or shop
diagrams. Cutting lifting holes on the job site
should be avoided. All stones shall have
identification numbers for erection purposes and
shall be shipped and stored in the sequence of
SURVEY, LAYOUT, AND FIELD MEASUREMENTS.
location of walls, door bucks, window frames, etc.
cannot be guaranteed, the job for the interior stone
installation shall be field measured, or certain
critical slabs shall be shipped over-sized for field
Exterior stone shall be prefabricated in compliance
with approved shop drawings.
Perimeter offset lines, column center lines,
benchmarks, and other necessary survey marks shall
be provided to the stone contractor for the stone
layout on each floor. Where possible, cuts or nails
shall be provided in the concrete floor rather than
paint or crayon marks.
critical phases of the installation procedure shall
be performed by qualified mechanics under the
supervision of a registered architect, engineer, or
consultant, who understands the anticipated
mechanical and thermal movements of the supporting
structure, the function of the gravity and lateral
anchors, and who knows the physical properties of
the stone being used. Supervisor shall be able to
recognize field conditions which deviate from the
specifications and/or shop drawings, and shall make
substitutions to meet field conditions or, if
necessary, stop installation until acceptable
measures or changes may be taken.
Close coordination is needed between the General
Contractor, the Stone Cladding Subcontractor,
Architect, Engineer, Stone Consultant, and Field
supervision personnel to make certain that all
components (inserts, gravity, and lateral anchors)
are located and installed as designed, within
allowable tolerances and that the type and number of
anchors used for stone cladding is in strict
accodance with the specifications and approved shop
PROTECTION, CLEANING, AND MAINTENANCE
cladding contractor shall protect stone slabs during
storage and installation, including protection of
exposed surfaces from scaffold tie backs, hanging
scaffold rollers, and possible damage from erection
tools and equipment. General Contractor shall
protect all stone set in place from possible damage
from other trades.
recommended that all exposed stone paving surfaces
and facing surfaces (minimum 8 feet high above
ground level) be protected with Homosote, or
18.2 Removal of
excess mortar, dust and dirt from the exterior stone
shall begin at the top, and be worked down. Stone
cladding shall be thoroughly washed down using clean
water and fiber brushes. Stonework with accumulated
dirt or substantial damage from industrial air
pollution may be cleaned by an approved cleaning
process employing properly pressurized steam and
For removal of
particular oil or grease stains, organic stains,
rust, or other miscellaneous stains, seek the advice
of a qualified experienced stone restoration firm.
It is recommended that all exterior exposed natural
building stone surfaces be washed down once every
five years. It is recommended that you contact
Building Stone Institute (BSI) for names of
qualified firms experienced in cleaning exterior
stone. During washdown, pointed or caulked joints
which may be damaged shall be raked and repainted or
and maintenance of marble and limestone require
different preparation than granite. To prevent
injury to marble or limestone, avoid the use of
solutions containing salts. Generally clean water is
all that is needed. However, from time to time, when
such treatment does not leave a clean and fresh
looking surface, a mild detergent and rinsing may be
18.4 A periodic
inspection and maintenance program can prevent
expensive renovation work or potential removal and
replacement of stone slabs.
The findings of
every inspection should be recorded so that any
progress in deterioration can be measured and
evaluated. Particular attention should be given to
stone joints, lips between stone panels, cracks or
19.1 In the
stone industry it is understood that in the process
of fabricating, shipping, and erection stone panel
damage and/or breakage may occur. It is an accepted
practice to repair damaged stone within certain
cracks and/or breakage sometimes develop - or may be
discovered - after the stone has been installed. It
is the accepted practice to repair such stones under
the supervision of an experienced and responsible
stone expert. Such repair work should be done by
qualified mechanics who have been instructed in the
proper procedure, usage of specified materials, and
cannot be repaired.
Any stone that has a crack, chips or break that
compromises or in any way affects the structural
integrity or the structural anchorage of the unit to
the backup is NOT to be repaired - but is to be
19.3 What can
Damaged stone that is determined to be repairable by
an expert may be repaired by one of the following
breaks less than 3/4" in depth.
Filling & Patching: For breaks larger than 3/4" in
Bonding: Adhesion of stone to stone.
This is a process where chipped or broken out areas
of stone are repaired by patching the void with an
epoxy mortar mix. This method is used where the
broken off pieces of stone are either not available
and/or the size of the chipped area is under 3/4" in
depth (see SK #1).
area is to be examined to determine if the size of
the break warrants, or can accommodate, "tie-in"
dowel pins (see SK #1& SK #2).
a) If the
condition to be patched is of a size where steel
dowel pins cannot be properly encapsulated with the
patch mix, provide an alternative "tie-in" by
drilling several 3/16" diameter "key-in" holes,
using diamond bits, at alternate approach angles
(plus or minus 1-1/2" o.c. plus-or-minus 3/8" deep).
This will provide a mechanical tie-in that is in
addition to the adhesion obtained by mortar mix (see
conditions where the size of the patch can properly
encapsulate steel dowel pins, prepare the area by
drilling 3/16" diameter holes, using diamond core
bits, at alternating approach angles (see SK #2).
Fill the holes
with epoxy mortar mix and insert 1/8" diameter
stainless steel dowel pins, allowing the dowel pins
to project out into the area to be filled.
c) If a limited
break occurs on the exterior portion of a continuous
kerf, dowel pins are to be used (see SK #3).
Note: Only exterior portions of continuous kerfs may
d) Place and
secure edge plywood framing as, and if, required
(see SK #1 & SK #2).
e) The area to be patched is to be clean, free of
dust and dry. The subject area should be kept free
from exposure to moisture for a minimum of 24 hours
prior to the repair operation. As an added
precaution, the subject area may be further dried by
the use of a hot air blow dryer for a minimum of 5
minutes just prior to proceeding with the patching.
f) Prepare an "epoxy mortar mix" consisting of an
approved bonding agent, and ground stone particles,
non-sag-consistency; fully fill "key-in" holes and
then fill in the balance of the chipped or broken
area. Texture the surface of this patch to resemble
the adjacent finish. Once the epoxy has fully set,
rough up or hone the surface to match the flamed or
honed finish to produce a matching texture.
When repairing polished surfaces, use a wrinkle-free
polyethylene sheet to obtain a smooth shiny finish,
or hand polish if necessary.
Where the chipped or broken out area is larger than
3/4" in depth and the broken off piece of stone is
not available, the area must be prepared by filling
in or building up the void area with a material
especially manufactured and formulated for this
particular application. Then, the final surface area
is to be patched and dressed using an "epoxy mortar
mix" as previously described.
a) Prepare the
area to be filled by providing a mechanical tie-in
by installing 1/8" diameter bent dowel pins at
alternating approach angles in the base stone (see
b) Place and
secure edge plywood framing as required.
c) Clean and
dry the area.
d) Prepare a
"fill mixture" of an approved bonding agent (without
any aggregate) and fill the void area completely
except the top, plus-or-minus 1/2". Allow some of
the dowel pins to penetrate out into this 1/2" area.
e) Allow the
"fill mix" to cure for a minimum of 24-hours. Then
patch the remaining area using an approved bonding
(see SK #5).
Bonding is used when an actual piece of the broken
stone is available to be reattached and bonded back
a) The broken off piece of stone is to be placed,
and temporarily held, in proper position on the
unit, and several 3/16" diameter holes are to be
drilled through the broken off piece directly into
the main base piece. The holes should be located in
the "meaty" portion of the broken off stone. The
depth penetration of these holes into the base piece
is to be plus-or-minus 3/4" (see SK #6).
drilling the holes, both pieces of stone are to be
cleaned and thoroughly dried using a hot air blow
c) Prepare an "adhesive mix" of an approved bonding
agent without any aggregate. Fill all the
pre-drilled "key-in" holes with the adhesive mix, as
well as both surfaces of the stone that will come in
contact with one another. Press fit the pieces to be
bonded together and insert stainless steel dowel
pins so that the pin engagement is approximately 50%
in each of the two pieces of stone. The exposed
access holes are to be patched using an approved
epoxy mortar mix with the appropriate colored
granulated aggregate to match the adjacent area.
Clean off any excess overflow and attach retaining
clamps if necessary.
d) Broken non-continuous kerf (single anchor kerf)
shall NOT be repaired. The stone should be replaced.
Continuous kerf (full length anchor kerf) broken at
the outside portion can be repaired only if the
broken part can be properly re-attached with the use
of stainless steel dowel pins. Such kerf repair
shall be analyzed and substantiated with signed and
sealed calculations by a licensed professional
When a cracked or broken stone is discovered on a
building - after installation - it can be repaired
by "stitching" if it is determined to be repairable
by an expert (see SK #7). To stitch a hairline crack
in a vertically installed stone facing, provide a
kerf cut in the exposed face of the stone, to a
depth half of the stone thickness, using a diamond
blade tool. The cut should be in the direction
perpendicular to the hairline crack to receive a
1/8" diameter, 2" long stainless steel dowel.
dowel in knife-grade epoxy mixed with stone powder
which will color the epoxy as close as possible to
the original color of the stone.
A minimum of
one stainless steel dowel is recommended for every
6" length of hairline crack in the stone.
If the crack is 1mm thick or more, then in addition
to the stainless steel dowel stitching of the slab,
provide a "V" grove 1/4" deep along the crack, and
fill it with epoxy mixed with stone powder.
In addition to, or in place of, "stitching,"
cracked, broken or loose stone can be pinned, if
determined to be repairable by an expert (see SK
To pin a
vertically installed stone facing, drill a half inch
diameter hole sloping down approximately 22°,
through the stone and its setting space into the
concrete backup structure.
Clean the hole with air and inject low consistency
epoxy in the hole in the stone.
Dip pre-cut stainless steel rod in epoxy and place
it in the hole of the concrete and the stone
approximately 1/4" short of the finished face of the
Fill the last 1/4" with epoxy and stone powder.
19.9 Materials and tools.
a) Patching: Use an "epoxy mortar mix" consisting of
an approved bonding agent with fine to medium grade
aggregate consisting of ground particles of the
actual project stone for the purpose of obtaining
and matching the original project stone.
b) Filling and Patching: "Fill mix" to be an
approved bonding agent with no aggregate added.
c) Bonding: Adhesive mix is to be made of an
approved bonding agent.
d) Stone Aggregate: Pre-packaged, dry, stone
aggregate of the project stone, of a color to
produce a mortar mix that matches the project stone.
e) Factory pre-packaged proportional units of an
approved bonding agent with the appropriate mixing
f) Stainless Steel Type 302 or 304 solid dowel pins
or threaded rods of various lengths - straight or
g) Other Equipment: Diamond drill bits, hot air
dryer, clamps, spatulas, polyethylene, tapes.