It wasn't that long ago that stone counters were an unusual
item only wealthy people could afford. They're still not cheap,
but they have come down in price and are increasingly common in
high-end kitchens and baths.
I've been in the stone-fabrication business for 20-plus years
and counters are one of our bread-and-butter items. Although
it's possible to fabricate counters in the field, you can do
much better work in a well-equipped shop. Mistakes are costly,
so we don't work from drawings or measurements. Instead, we
make full-size templates of the cabinet top and take them back
to the shop, where they are used to cut pieces from large slabs
of stone. When the pieces are finished, we take them to the
site and use epoxy to glue them on top of the cabinets (see
Counters are transported to the site in
sections and glued to a plywood subtop with thick dabs of
epoxy. This counter is made from 13/16-inch material. There
would be no need for a subtop if it were made from 1 1/4-inch
Our work happens late in the job, and counters tie in to the
work of many other trades. The tolerances are exacting, so it's
not uncommon to run into trouble because something isn't ready
or because the details are not fully worked out. This can cause
delay at a critical point in the project, or lead to added
costs because existing work has to be redone. The purpose of
this article is to explain what contractors need to know about
stone counters so they can avoid these problems and create a
product the client will be happy with.
Granite is the most common stone used for counters, but there
are many other slab materials to choose from. We often use
marble, limestone, onyx, slate, and quartzite. Some of these
materials are interchangeable, but others require special
detailing, either in the stone counter itself or the cabinets
below. My advice is to start talking to the fabricator early in
the job. A knowledgeable fabricator can explain the pros and
cons of various materials and tell you what it will take to do
a successful installation.
Most slabs are imported, so they come in metric thicknesses.
In the industry we talk about 2-centimeter and 3-centimeter
stone. That converts to roughly 13/16-inch and 1 1/4-inch
material, which is how I will refer to it in this article. In
most of the U.S. the thinner, "dimensional" stone is the norm.
However, there are areas on the East Coast and in the South
where 1 1/4-inch stone is more common.
The clients can wait to select the particular piece of stone
they want to use, but every other decision must be made before
we arrive to make templates. The cabinets and subtop should be
complete, and the sink, cooktop, and faucets should be on site
and temporarily installed in their future positions. If there's
a freestanding stove, it too should be in place.
Some fabricators make templates by putting strips of plywood
along the edges of the subtop and connecting them with hot-melt
glue. We make them from full pieces of 1/8-inch plywood,
because the glue joints could get knocked out of whack on the
way to the shop. If the counter butts to an irregular surface,
we scribe the template to fit.
Every detail of the installation is recorded on the template,
including edge treatments, overhangs, and the size and location
of penetrations. The counters will be identical to the
templates, so changes are not allowed once the templates are
made. If the client changes something, we have to come back and
retemplate the job.
Stone is heavier than many of the materials traditionally used
for counters. A 13/16-inch slab weighs 13 pounds per square
foot and 1 1/4-inch material weighs 19 pounds per square foot.
This is not an incredible amount of weight, but it does mean
that base cabinets should be sturdily constructed.
I have visited projects where cabinets failed because they
were not strong enough to support the load. In one case this
happened because an island cabinet was made from MDF. A 1
1/4-inch slab was supported by an end panel that landed over a
toe kick. The end panel was strong enough to support the stone,
but the bottom broke where it cantilevered over the kick
(Figure 2). It wouldn't have happened if the bottom had been
stronger or the panel had run straight to the floor.
Figure 2.Cabinets should be designed to support
heavy stone counters. MDF is fine for the sides but may not be
strong enough to carry a large thick slab that lands above an
Subtops. The biggest
difference between using 13/16-inch and 1 1/4-inch stone is
that the thicker material is structural. "Structural" stone is
strong enough to be installed over open cabinets and can span
openings without any additional support. The one rule for
13/16-inch stone is that it is only as strong as what you apply
it to. Dimensional stone should be installed over a continuous
plywood subtop that is solidly screwed to the cabinets.
The subtop should be made from 5/8-inch plywood, not
particleboard or MDF. Plywood is stronger and resists moisture
better. The last thing you want is for the subtop to swell or
fall apart because it gets wet.
Overhangs. There's a limit
to how far an unsupported dimensional stone overhang can
project. According to the Marble Institute of America (MIA),
13/16-inch material should not extend more than 4 inches
without support. The thicker, 1 1/4-inch stone is allowed to
have an 8-inch unsupported overhang. You could probably go
further with the right kind of stone but you would be taking a
chance, especially if the MIA installation guidelines are part
of the contract.
Deep overhangs are common at breakfast bars but they need to
be supported from below. I tell contractors to sit on the edge
of the subtop, and if it deflects more than 1/8 inch it's not
sufficiently stiff. The easiest way to support the overhang is
to put end panels or decorative brackets underneath. If the
client doesn't want brackets or panels, you will have to devise
a less obvious means of support. In this case, we use concealed
angles or plates. My favorite method is to route slots in the
subtop and insert steel angles so they are flush with the
surface. It will probably take several angles to sufficiently
stiffen the overhang. The pieces will cantilever over the edge,
so one-third should be in the overhang and two-thirds should
land on the cabinets (Figure 3).
Here, the installer applies epoxy to
steel angles in the subtop that will support an overhanging
section of counter (top). Another way to stiffen the overhang
is to support it from underneath. This section of the subtop
(bottom) is carried by steel plates that span the top of the
We typically double the front edge of dimensional stone
counters to make the material look thicker. The added layer
also forms a lip that is supposed to hide the edge of the
subtop. However, lumps in the subtop and the thickness of the
epoxy may prevent the stone from lying tight. That is why the
subtop is made from 5/8-inch plywood: If it were any thicker
the nosing might not hide the edge.
Some designs call for an even thicker edge treatment. It's
common to miter the front edge of the counter and glue on a
strip of stone that is 2 or more inches wide. In that situation
it's okay to use a stronger, 3/4-inch subtop, because the lip
will be tall enough to hide it.
Dimensional stone is sometimes installed with a
single-thickness edge. There's no lip, so the subtop will be
visible unless you tuck it behind a face frame or edge it with
trim (Figure 4). Structural stone is thick to begin with, so
it's almost always fabricated with a single-thickness edge.
There's no need for a subtop; the stone is applied directly to
Figure 4. Cabinets
should be constructed with the edge detail of the counter in
mind. When a plywood subtop is used, it will be necessary to
hide its edge. Sink mounting details should also be
Close tolerances. The
tolerances for installing stone counters are very exacting, so
it's important for the cabinets to be perfectly level and for
the subtops to form a single level plane. The reveal between
the nosing and the cabinet fronts will not be even if there are
lumps or bumps in the subtop. We can level the slab to some
extent, but that means raising it and creating an oversize
It's easy to cut openings for drop-in sinks because the flange
hides the edge. It takes more work to finish the opening for an
undermount sink. Even so, undermount sinks are the norm with
slab stone counters.
The tricky part for the contractor is figuring out exactly how
to support the sink. It needs to be supported by the cabinet
and is much easier to install from above before the counters go
in. The lip of the sink is typically rabbeted into the subtop
and supported from below with cleats or hardware designed for
that purpose (Figure 5).Figure 5. Undermount
sinks are supported from underneath the rim. In this kitchen,
the front and back edges of the sink will be carried by the lip
that is formed between the stretcher and the plywood subtop.
Each end will be carried by an adjustable metal bracket