Installing Stone Counters, continued

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 (Figure 6).

Figure 6. Here, a fabricator is tracing the location of a sink onto the bottom of a plywood template. The opening through the stone will be sized down to create the proper overhang.

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). 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 (Figure 8).

Figure 7. The edge of this counter has been strengthened by gluing metal angles to the back of the nosing. The entire slab has been reinforced with a layer of fiberglass mesh and glue.

Figure 8. The stone will be narrow at the front of this sink, so the carpenter reinforced that area by installing a horizontal apron across the top of the opening. A center stile would perform the same function in a face frame 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.

Faucets

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 (Figure 9).

Figure 9. Sinks and faucets must be located and temporarily installed in the subtop before the templates for the counter are made (top left and right). Here, the author is verifying that the homeowner is satisfied with the location of the faucet (bottom).

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 (Figure 10). 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.

Figure 10. The top piece is a 1/8-inch plywood template that has been cut to match the opening in the subtop for a cooktop and downdraft vent. The vent is not as wide as the cooktop, which is why the opening is narrower at the back.

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 (Figure 11). The stove should remain in place until the counters are installed. That way, we have something to align them to.

Figure 11. Freestanding stoves should be installed before templating. Otherwise, there could be an uneven gap between the stove and counter. The fabricator is measuring to see if the stove is square to the opening.

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. Rick Stenberg is the owner of Marin Marble in San Rafael, Calif.