The beauty and permanence of natural stone countertops are enjoyed by many. The full potential of any installation is realized only when the selection, design, fabrication, and installation are completed by, or with the consultation of, qualified and experienced individuals. This document has been prepared and published by Corsi & Nicolai (Australia) Pty Ltd to help guide consumers through the process professional fabricators use when using natural stone as a countertop surface.
Varieties. Many varieties of natural stone have been used successfully for countertop surfaces.
However, different types of stone have specific properties that offer advantages or disadvantages in various applications. The following is a brief overview of the common varieties of stone used as countertops. Granites are undoubtedly the most popular stone type used in countertop applications today. This group of stones includes many stone materials that are not true granites by geological definition. However, because their properties are so similar, the American Society for Testing and Materials International (ASTM) lumps them together as ‘granite’. These stones are known geologically as gabbro, anorthosite, gneiss, diabase, and diorite, to name a few. Whatever the name, these stones are some of the hardest of the common countertop stones, offering high levels of resistance to abrasion and scratching. The primary minerals in granite are resistant to almost all chemicals commonly found in a home; however, there may be trace minerals present in some granites and granitelike stones that are vulnerable to some acids.
Marbles, serpentines, and onyxes are traditionally prized for their aesthetic appeal, accentuated by distinct veining and often bold colours. They are relatively softer than granite, although some serpentines are as dense as some granites. Marbles can be scratched by kitchen utensils so it is best to use cutting boards and other protective measures. Use only nonabrasive products when cleaning marble.
Marbles can also be etched by chemical attack.
These stones are calcium carbonate based and are damaged by exposure to acidic solutions such as lemon juice, tomatoes, vinegar, etc. The use of inappropriate cleaning agents may also trigger acidic attack.
Acidic solutions can permanently etch the surface of the material. The application of a sealer will reduce, but not eliminate, the vulnerability to acidic attack.
Slates have high resistance to chemicals and have been traditionally used as chemistry laboratory tops. However, slates are softer than granite and therefore vulnerable to scratching and abrasion. Slate has a natural cleft (not a smooth surface). Some suppliers provide slate slabs that are not honed. Be specific about the kind of finish you desire.
Documentation. As dictated by standard practices of good business,
all communications MUST be documented in writing. All natural stones are
unique. Some have pits, fissures, cracks, corrosive minerals, or other features
that you may find objectionable.
These should be acknowledged and pointed out to you when samples
and/or slabs are being viewed. You need to be aware that some of these features
may become more or less noticeable when the position (vertical or horizontal)
of the slab is changed, or when the lighting intensity is changed.
You and Your Subcontractor’s Responsibilities.
Cabinetry installation, plumbing rough-in, electrical
rough-in, etc. are usually required to be completed by you, or by
subcontractors coordinated by you.
These should be specifically addressed in writing. Your
stone contractor will install your stone, not connect electricity or water.
Granite is heavy! Please have a clear
path from your driveway to your kitchen so that installation crews can navigate
through your home easily. Also, if you have existing countertops, please make
sure they are removed BEFORE installation. Also, make sure that your installation
date does not conflict with other work being done in your home (wood floor finishing,
tile installation, other tradesmen, etc.).
Shop Drawings can effectively
communicate exact cutting information to you. A shop drawing is a highly
detailed document that will identify all aspects of the finished product installation.
The shop drawing is prepared by your fabricator, showing the layout of the
stone pieces, location and size of all seams, and details clarifying all corner
and edge treatment conditions. Some fabricators produce full size templates
that are highly detailed. These detailed templates may be considered “full
size” shop drawings. Whatever the format, you will review and approve this
document prior to the start of fabrication. This is the time to ask questions
about seam placement, cutouts, etc.
Stone Slab Layout. When working with
highly variegated materials, insist that you participate in the layout of the
actual stone slabs. This is very important and highly recommended so that you
can fully understand what can or cannot be done. Keep in mind that the pricing
may change if you decide to have the stone cut in a certain way that causes
unnecessary waste.
Cabinets and any trim that affects the
overall size of the stone countertops must be permanently installed in their
final position prior to field measuring for countertops.
Measurement Tolerances. Top surfaces of
the stone cabinets must be within 3 mm of flat and level when measured across a
distance of 3m.
Wall surfaces to receive stone
backsplashes must be plumb and within 3 mm of a true plane when measured across
a distance of 3m.
When cabinets are not within these
tolerances, you (or your Authorized Representative), will be asked for
permission to proceed with the installation. Installing cabinetry outside of
these tolerances will require excessive shim spaces and wide regions of filler
material. Any necessary aesthetic improvements to conceal this condition (e.g.,
additional wood trim) may be your responsibility.
Subtops. Fragile stone varieties may
require a full subtop to support the stone. Generally, sound varieties of
granites and marbles can be used in thicknesses of 20 mm or greater without the
use of a subtop. However, the presence of aesthetically pleasing but unsound
veins, cracks, or excessive fissuring will mandate the use of a subtop,
regardless of thickness. Appropriate materials for subtops are marine-grade
plywood, exterior grade plywood, waterproofed medium density particle board, or
furring strips.
Excessive weight requirements, like
that of a heavy cast-iron sink, may require the use of either a subtop or
auxiliary framing to carry the weight of the sink and its contents. Water
weighs around 1 Kg. per litre. Some of the larger sinks can easily hold 45
litres or more.
That’s an additional 45 Kg (or more)
hanging under your counter!
Cabinet doors, end panels, and hardware
must be installed before the field measurements are made. Upper cabinets are
usually required prior to installation if a full height backsplash is to be installed.
If not, then it is best to position them after the stone installation.
Cabinet Components. Field measurements are taken once all cabinets have been installed in their permanent positions. The following related components must be available to the Technician at the time of measurement (templating):
Joinery Layout (Seam Placement). The
layout of the joinery (seams) of the countertops is extremely important to the
overall appearance upon completion. Make sure you understand where seams will
be and how seams may affect the overall appearance of the stone. This is especially
true when installing some of the higher-end varieties with obvious veins and movement.
Spans and Cantilevers. In designs where
part of the countertop is spanning between supports, the length of the span
shall be limited to 600 mm for 20 mm stone thicknesses 900 mm for 30 mm stone
thicknesses.
In designs where the countertop is
cantilevered or overhanging the supports, the cantilever shall be limited to
150 mm for 20 mm thick countertops and 250 mm for 30 mm countertops, but in no
case may the cantilevered portion represent more than 1/3 of the width of the
countertop.
Cantilevered countertops exceeding
these dimensions will require corbelled supports beneath the stone. The exposed
underside of cantilevered portions of countertops will be sawn or otherwise
unfinished surfaces.
Note:
Fragile stones may require corbelled supports for cantilevers that are
less than those specified.
Sink Mounts. Sinks are supplied in one
of several types: Top mount, (or self-rimming), under-mount, and “farm-home.”
In the case of the top-mounted sinks, the weight of the sink and its contents
are transferred to the top surface of the stone counter via the rim of the
sink.
Undermount sinks can be anchored to the
underside of the stone countertop or carried by a subtop. A subtop or auxiliary
framing may be required for either design when more fragile stones are used, or
when the sink (with contents) is excessively heavy.
Note: cast iron sinks will always
require the extra support stated above for both top and undermount types.
Edge profiles or silhouettes; add
elegance to the finished project. Edge profiles with narrow projections and
sharp corners are more susceptible to chipping than those with a larger, curved
silhouette. Examples of edge profiles commonly used are included on drawing.
With machinery and tooling available to modern fabrication shops, many custom
profiles can be created which are not shown here. Ask your fabricator if you
have something special in mind. Your selection of an edge detail will likely
influence the cost of your countertops more than any other decision you make.
Corner Embellishments. Corners of stone
countertops can be cut square, cut to a radius, or projected.
Back-splashes. Partial back-splashes
usually range from 100 mm to 200 mm high.
Full-height back-splashes cover the
entire area between the countertop and the upper cabinets.
Back-splashes are normally made of the
same thickness as the countertop material. This allows the Fabricator better
yield from the slabs, as the narrow strips will aid in the layout efficiency, and
it also provides better colour match. Mixing materials of two different
thicknesses requires using stone slabs sawn from two different blocks, and colour
variation can be pronounced.
However, some Fabricators have the
machinery to plane down back-splashes using the same slab or block of material
to get a thinner splash and match the rest of the counters. On stones with obvious
veining, the vein of the splash should match the countertop below.
Back-splashes are not assumed to be part
of the job and must be specified if you want them.
Finishing Edge Profiles. Professionally
finished edge profiles will be a constant thickness and smooth along the entire
length.
Edges are finished to the same type and
quality of surface as the top, unless a contrasting edge surface has been
specified for accent purposes.
When working with resin treated slabs,
exact colour match between the edge surface and the top surface may not be
achievable.
Cutouts for auxiliary equipment must
conform to equipment templates, with allowable tolerances. Please verify that
the equipment templates match the equipment you are installing. There have been
cases where the supplied manufacturer templates did not match the sink,
cooktop, etc. In the interest of safe handling, some cutouts may be partially
or completely performed in your home after installing your stone.
Dry Assembly. At the project site, it
is recommended that all stone pieces be “dry assembled” in place to verify
satisfactory fit prior to the application of adhesive.
Shims are commonly employed to level
the stone countertops. Shim material may be wood or plastic. Maximum spacing
between shims is 600mm. Alternatively,
longer spacing between shims may be used if the stone is supported with a
non-compressible filler material (usually epoxy or polyester resin). This
practice is often referred to as “hard packing.”
Adhesive. The stone countertops are
secured to the substrate with a non-staining adhesive.
Common construction adhesives or
silicone sealant are the most popular materials used.
Final Positioning and Joint Filling.
Final positioning of the stone is done either manually or with the aid of
commercially available stone alignment tools. Filling the seams is normally completed
prior to final positioning of the stone units, allowing the filler material to
extrude out of the joint as the stones are pulled into alignment. The stone
surface may be masked to prevent contact by the filler material.
Sealer Application. After the
countertops are installed and the seams are filled, a sealer or impregnator may
be applied. Refer to the Reinforcement Techniques section below for further
discussion of these applications.
Alternatively, some fabricators prefer
to apply the sealer or impregnator in the fabrication shop prior to
transporting the pieces to the project site.
The tolerances listed here are achieved
using skilled tradesmen following standard industry workmanship practices. Due
to variations in fabrication equipment and stock availability, these tolerances
may not be achievable, or in some cases, closer tolerances may be achievable.
Therefore, for any particular project, you and your contractor may agree to
tolerances that are more or less stringent than those listed here. Such
agreements should be documented in writing. Unless otherwise agreed, the
tolerances listed here are acceptable guidelines.
The tolerances in this section pertain
to large stone panel-type countertops only.
Tolerances for stone tile countertops
are listed below, in Adhesives and Joint Fillers.
Joint (seam) widths between two stone
units should equal 1.5 mm, with a tolerance of ±0.4mm. In such cases where a
larger joint width has been specified, the tolerance is to be ±25% of the
nominal joint width. Joint width does not include the dimension of an arris (a
small chamfer, approximately 1.5x 1.5 mm) on the stone edge. When an arris is
used, the perceived joint width may be greater than the actual width due to the
seam filler occupying the width of the arris.
Lippage. In the stone industry, the
term “lippage” refers to the unevenness of the finished surfaces of two
adjacent stone units.
Due to the relatively tight seams used
in countertop installations, even minor amounts of lippage are noticeable.
Lippage may be unavoidable due to permanent warp in the slab stock. There
should be no detectable lippage at the front or rear edge of the countertop.
Maximum allowable lippage at the centre
of the countertop is 0.8 mm).
Slab Thickness. The thickness of the
stone slabs used in a given project shall not vary by more than 3 mm between
the thickest and thinnest slabs.
Exposed edges of adjacent stone slabs
must be matched in thickness and properly installed so that neither the top nor
bottom surface exceeds lippage tolerances.
Joints at Materials Transition. Visible
joints between stone and other materials (e.g., cabinetry, gypsum wall board)
shall be 3 mm, with a tolerance of ±1.5 mm, and filled with a soft, elastic
material.
Exceptions to this would be the joint
between a full height backsplash and the underside of the upper cabinets, which
is to be a nominal 6mm with a tolerance of ±3 mm. Concealed joints between the
stone and other construction materials (e.g., stone-to-wall joint underneath the
backsplash) shall be sized to ensure a minimum of 3 mm of cover.
Slab Flatness and Levelness. Individual
stone slabs are to be flat within 1.5 mm when measured with a 1.2 m straight
edge. Finished countertop surfaces including multiple stones are to be both flat
and level to 3 mm across 3m.
Types. Adhesives used for stone
installation can be either standard construction adhesives or elastic sealants
with strong bonding properties to both the stone and the substrate.
Construction adhesives will normally provide greater bond strength, while
elastomeric sealants will provide some forgiveness for movement within the cabinet
and subtop underneath. Excessive movement of the substrate, regardless of the type
of adhesive used, will result in the cracking of seams or the stone itself. Verify
that the product used does not stain the stone material.
Seam Filler Materials. Seams in the
stone countertop are usually filled to the level of the top surface. The most
common filler materials are polyester resin, epoxy resin, elastomeric sealant,
and grout. Elastomeric sealants can be made from silicon, polyurethane, or
acrylic bases.
Subtops. Stone tile countertops must
have a subtop made of minimum 20mm exterior grade plywood or "cementitious”
backer board.
Subtop must be flat to within 3mm in 3m.
Edge Treatment. Exposed edges of the countertop
may be finished by providing an edge profile strip of stone, wood, or metal.
Where stone is employed, it is to be
used as an apron to the top surface stone, which limits stress on the
countertop/apron joint.
Stone tile tolerances for all stone
types must be 1 mm in length, width, and thickness.
Joint Widths. Unless otherwise agreed,
joint widths for stone tile countertops must conform to the following:
Stone-to-wall joints must be 3mm in width. Stone to- stone joints must be 1.5 mm
minimum, 2 mm maximum, and uniform from stone to stone. Stone-to cabinetry
joints must be 3mm in width.
Vein Trend. When using stone tiles with
obvious veining, all tiles shall be installed with the vein running in the same
direction.
Shading Variation. Stone tiles are
subject to manufacturing processes different from structural stone. There is
great latitude in the acceptability of shaded stones. Ask the Installers to lay
out the stone for your inspection and approval.
Splashes must be stone tile, minimum of
100mm high.
Back buttering of all stone tiles is
required. This technique applies a portion of the installation material to the
back face of the stone. It requires placement of one-half of the setting
material in the case of thin-set mortar, epoxy, or non-water soluble adhesive,
or a lesser quantity of very rich mortar in the case of Portland cement, to the
back of the stone, while the balance of the setting material is applied to the
bed.
Application should be performed so that
one pass is completed in a north-south direction, while the second pass is
performed in an east-west direction, thus ensuring, as close as possible, 100%
contact of the stone to the installation bed.
Tile Reinforcement. A common
reinforcement for fragile stone tiles is to apply a fiberglass mesh to the back
surface of the tile. The adhesive used in this application is commonly an epoxy
or polyester resin.
When this type of reinforcement is
adhered to the tiles, the Installer must use a thin-set material that will bond
to the resin impregnated backer. Most often this will require an epoxy based, rather
than a Portland-based, thin-set compound.
The application of resin to the
surfaces of stone slabs has become an ever-increasing practice.
The intent of this procedure is to fill
pits, cracks, and fissures of natural stones with a glossy resin to enhance the
appearance of the polished slab.
When received, the resin treatment is
usually easily detected by viewing the raw edges of the slab. Evidence of
excess resin is usually visible on the edges of the slab if the stone has been treated.
Description of Procedure. The process
involves evenly applying the resin on the surface of the cleaned, sawn slab.
This is frequently done in an automated process, although some suppliers will do
this manually.
Depending on the equipment used, the slab may be placed over a
large vacuum table to draw the resin deeper into the stone.
The resin is allowed to cure, which may
or may not be accelerated with heat application.
Once the resin has cured, the slab is
polished.
The polishing grinds most of the resin
from the stone surface, so that it remains only in depressions and some
inter-crystalline regions of the slab. The amount of surface area that remains
as resin varies due to the natural features of the material, but it is usually
a fraction of one percent (1%).
The resin used in this process is
commonly an epoxy, polyester, or acrylic based polymer.
Design Considerations. While the intent
of this process is to provide a cosmetically more attractive surface, you
should be aware of several characteristics of resined stone:
As products of nature, stones have
varying strength and behavioural properties. Stones of lesser soundness or
stones that have had substantial areas removed from the slab (e.g., sink
cutouts) will benefit from reinforcement by a variety of techniques.
Fiberglass Mesh. A common reinforcement
for stone slabs of limited soundness is to apply a fiberglass mesh to the back
surface of the slab.
The fabricator completes this process
in the shop. The adhesive used in this application is commonly an epoxy or
polyester resin.
Liner Blocks. Although not frequently
used in stone countertop construction, a liner block of stone material can be
adhered to the underside of the stone slabs (when no subtop is used) to reinforce
seams or other vulnerable areas. The liner block need not be of the same type
of stone material as the countertop.
Splines. Seams, particularly those
between narrow stone pieces, are often put together using a steel or stainless
steel key.
Commonly, a large washer is used as the
spline key. The metal is fully encapsulated with polyester or epoxy resin and
fitted to closely cut slots in the stone, similar to the “biscuit” joint reinforcements
used in woodworking.
Rodding. A commonly seen method of countertop
reinforcement is the technique referred to as “rodding.” Rodding is beneficial to
narrow strips of stone material, such as those in front or behind sink or cook
top cutouts. This technique requires a shallow kerf (a narrow cut or groove) in
the underside of the stone slab.
The kerf is then closely fitted with a
metal or fiberglass rod, which is then fully embedded in epoxy or polyester
resin. The rod has greater resistance to bending than the stone and helps prevent
the stone from bowing. A strip of fiberglass mesh backing is often applied over
the rodded region for additional reinforcement.
Stone countertops in need of repair
require competent, experienced artisans to achieve the desired results.
Repairing stone is permitted when the refurbished region is not in a structurally
significant area of the countertop, and when it can be accomplished skilfully
so that the repair is consistent in colour and texture with the rest of the
slab.
Fissures occur naturally in many stone
types. A fissure is defined by the American Geological Institute as “an
extensive crack, break, or fracture in the rock, which may contain mineral bearing
material.” The term “fissure” is used commercially in the stone industry to
describe a visible separation along intercrystalline boundaries or the voids
between mineral crystals. This separation may start and stop within the field
of the stone or extend through an edge. A fissure differs from a crack in that
it is a naturally occurring feature in the stone.
Cracks occur in stones as a result of mechanically
induced stresses during handling, fabrication, transport, or installation. When
cracks are detected in slab material prior to fabrication, the best method is
to simply avoid them during the layout process. In stones with lesser soundness
properties, this option may not be practical, or possible. When working with such
stones it is common practice to repair cracks by cementing them together with
epoxy or polyester resin, either with or without dowel reinforcement. Cracks
that occur as a result of handling-induced stresses are often more difficult to
repair, as they commonly include chipping in addition to the crack. Repair is frequently
performed by injection of a penetrating resin adhesive, which may be dyed to
match the stone, and then rebuffing the area after curing of the resin. In many
cases, the entire stone must be repolished to make the repair unnoticeable. If
the repair is attempted but unsuccessful, the stone is to be replaced with a
new piece.
Chips can occur in stones either as a
result of sawing operations or handling and restraint devices. Particularly in
the igneous stone varieties, the exiting portion of the diamond blade will
create many small chips. A small chamfer, called an arris, of approximately 1.5
x 1.5 mm can be used to eliminate most of these small chips. The use of an
arris will make the seam appear wider than its actual dimension when filled.
Larger chips may be repaired with epoxy
or polyester resin if the completed repair is consistent in colour and texture
with unrepaired areas of the slab. In many materials, the resin used in the
repair will appear more natural if it is not dyed.
Pitting of the countertop surface,
particularly in granite material, is a commonly seen characteristic on natural
stone. Granites are made up of several different minerals, each mineral having
a different hardness. Granites contain quartz, feldspars, biotite, amphibole, ferrous
titanium oxides, and other mineral combinations. On the Mohs Scale, diamonds
are the hardest mineral, with a rating of 10. Quartz and feldspar have a
hardness of 6.5 to 7 and are very durable. Biotite (also known as mica) on the
other hand is very soft (2.5) and flakes easily. All true granites have biotite
in their composition. Because biotite is relatively soft and flaky, the first
few layers are removed during the polishing process, causing pits throughout
the slab. Some granites have more biotite throughout their composition than
others.
The higher the biotite content of the
stone, the more pits it will have. Most polished igneous rocks will have
varying degrees of pits, depending on the amount of biotite, muscovite, and
phlogopite in their composition.
The pits do not make the granite less
durable or otherwise inferior, and do not in themselves qualify the slab for
replacement.
Pits are common in all granites and
should be expected when dealing with a natural, polished stone containing
several types of minerals of varying hardness. It is usually best to not attempt
repair of pits, as most repair techniques will not cosmetically improve the
countertop.
Application of Sealers. The application
of a topical sealer or impregnator is a common step in decreasing the
vulnerability of the stone to stains.
Topical sealers cure as a film on the
stone surface. Since the material is actually covering the stone, the
appearance of the stone surface may be altered by the application of this type
of product. This material will provide somewhat of a sacrificial layer over the
stone, and will absorb most of the wear on the countertop.
Since the sealer is softer than the
stone, normal use of the countertop will result in abrasion of the sealer
surface and dictate reapplication to maintain the original lustre of the
surface. A properly applied topical sealer will normally reduce, although not
eliminate, the vulnerability of calcareous stones to attack from mildly acidic solutions.
Impregnators will penetrate the stone
and cure a few millimetres below the surface, residing in the microscopic
spaces between the minerals in the stone. These products do not actually “seal”
the stone, and are more correctly referred to as a repellent rather than a
sealer. As such, they are formulated to prevent transmission of liquids, while
allowing transmission of vapour (not unlike ‘breathable’ fibres). Since they
reside below the actual surface of the stone, the change to the appearance of
the stone surface is minimal. Impregnators will be either hydrophobic, in that
they repel water-based fluids only, or oleophobic, repelling both oil and water-based
fluids. The Manufacturer of the impregnator product will recommend a reapplication
interval.
General Precautions. When any surface protection
product is used, care must be taken to read and follow the Manufacturer’s
written instructions accurately. This will provide the greatest benefit from
the application and will guarantee safe handling of the product.
Care and cleaning practices. The
natural stone you have purchased for your home or office is an investment that
will give you many years of beautiful services. Stone is a natural product and simple
care and maintenance will keep it looking beautiful. Make sure you understand which
methods are best for your particular stone countertop.
