How Installing stone counters – part 2

How Installing stone counters

Edge Details

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. 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 the cabinets.

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 reveal.

Undermount Sinks

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.

The sink should be installed flush with the subtop, because the counter is supposed to land on or just above the flange. Sink holes will vary, because they are ground and finished by hand; they need a little bit of play. The hole in the subtop should be slightly oversized, big enough to shift the sink 1/4 inch in any direction. This allows us to adjust the sink to the opening when we install the counter. The counter usually overhangs the sink, and the joint between the slab and flange gets caulked.

Unlike many fabricators, we will not cut a sink opening from the paper template that comes with the fixture. Every now and then someone will give us the wrong template, and we don’t want there to be any question about where the opening goes. We want the sink to be in place when we template the cabinets so we can trace the opening onto the template.

Stiffeners. Counters are weakest at the narrow strips of stone along the front and back of large cutouts. We sometimes reinforce these areas by slotting them from the bottom and epoxying in a metal rod (Figure 7, facing page). It’s also a good idea to stiffen the subtop under narrow strips of stone, You can do this by installing aprons or posts inside the cabinet.

A cast iron sink is very stiff, so if it’s held up by the cabinet it will provide some support to the strips of stone above. Stainless steel is another matter. I will not put stone across the divider of a double bowl stainless steel sink unless there is some kind of reinforcing below.


Some fabricators drill the faucet holes in the field. They fear that the counter, weakened by holes, may break in transit. We prefer to drill holes in the shop, because drilling creates a lot of dust and we haven’t had much trouble with breakage.

We can’t make templates until we know exactly where the faucets will go. Faucets should be dry fit in the subtop with the sink in place. It’s usually a tight fit, so it’s important to make sure everything works. Be sure to consider the thickness of the backsplash. It’s a good idea to temporarily install the sink and faucet and show them to the clients. Let them manipulate the faucet, and get them to sign off on the location of everything. It’s not hard to move things at this point, but once we fabricate the counters the faucet locations will be literally carved in stone.

Clearances. The holes through the subtop should be the same size as the holes that will be drilled in the counter. The faucets should be test fit with the sink in place, because you want to be sure they are not too close to the flange. If they are, the plumber will not be able to install the nuts and washers that hold them in.

Once the counter is templated, you may want to cut out the material that’s under the faucet holes. Most faucet stems do not have enough thread to reach through the counter and the subtop and stretcher below. If you remove this material, the plumber can run the nuts to the bottom of the slab.

Cooktops and Vents

Cooktops are usually easy to put in, because they install from above and have a flange. It’s tougher if the client wants to use a cooktop with a separate downdraft vent. Frequently the two appliances come from different manufacturers, which can make for a tight fit in the cabinet. Most vents are slightly narrower than cooktops and are equipped with a minimal flange. There’s not much play, so you need to test fit the units to make sure they fit in the opening and that the flanges will hide any gaps. Some vents have top and bottom flanges that slip over the stone to hold the unit in place. They work fine with dimensional stone but are not sized to fit thicker material. If you want to put this type of vent in a 1 1/4 inch slab, you’ll have to cut off the bottom flange.

Sometimes there’s an opening in the counter for a freestanding stove. The stove will not be attached to the counter, but we still expect it to be on site when we make the template. We will not work from cut sheets because the dimensions are frequently incorrect and appliances are allowed to vary slightly from spec. Sometimes they are not even square. The only way to get a good fit with an even reveal is to put the stove where it goes and template to it. The stove should remain in place until the counters are installed. That way, we have something to align them to.

Even though it’s not supposed to show, we polish the cut edge of the counter that butts to the stove. If the stove is slightly low, the client will see a polished edge.

Cover Your Costs

If you’re the GC, you will need to carry something in the budget for tasks that relate to the installation of stone counters. Someone needs to build the subtop and to pre install the cooktop, sink, and faucets. The schedule will be affected, too. The fixtures, faucets, and appliances need to be on site earlier than usual. The client should be aware that there will be a two to three week lag between templating and when the counters go in.

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