How to install prefab stone countertops

Before you start

Every piece is 2 cm (about ¾ inch) thick, with a mitered or laminated front edge, built up so the front looks thicker. MSI says 2 cm stone needs a ¾-inch plywood sub-top underneath, which also brings it up to standard counter height.

Installing stone is heavy, precise work. If you do not have a wet saw or a water-fed grinder with diamond blades, two strong helpers, and a way to carry pieces upright, have a contractor do it. We can reach out to our installation partners to find you a quote.

Tools and materials

• Wet tile saw or a water-fed angle grinder or circular saw with a diamond blade made for stone
• Diamond core bits for faucet holes
• Respirator rated for silica dust, safety glasses, hearing protection and gloves
• Level, straightedge, tape measure, clamps and shims
• ¾-inch plywood for a sub-top if the stone is 2 cm thick
• 100% silicone adhesive, and color-matched stone epoxy for seams
• Seam setter (suction cups) if you have long seams
• A penetrating stone sealer for natural stone

Step by step

1. Prepare the cabinets. Remove the old top, then shim the cabinets level front to back and side to side. Add blocking or a full plywood sub-top where the stone is thin or the span is wide.
2. Measure and mark. Lay out each piece with the finished edge to the front. Plan seams away from the sink and cooktop, over a cabinet wall where both pieces are supported. See how to measure for countertops.
3. Dry-fit. Set the pieces in place without adhesive to check the fit against the wall and at each seam. Scribe the back edge where the wall bows.
4. Cut to length. Support the piece fully on both sides of the cut. Cut slowly with plenty of water, finished face up for most blades, and tape the cut line to reduce chipping.
5. Cut the sink opening. Use the template from the sink maker. For an undermount sink, cut the opening, then smooth and polish the exposed edge. Drill faucet holes with a diamond core bit, kept wet.
6. Set the pieces. Run beads or dabs of silicone along the cabinet tops or sub-top, lower the stone into place and check level again.
7. Make the seams. Clean both edges, fill with color-matched epoxy, pull the edges flush with a seam setter, and scrape off the excess once it cures.
8. Mount the sink. Undermount sinks hang from clips or brackets epoxied to the underside, plus a bead of silicone; follow the sink maker’s instructions.
9. Seal and finish. Seal natural stone once the adhesive has cured, then caulk the backsplash joint.

Mistakes to avoid

• Carrying a piece flat. Stone is strong on edge and weak flat; carry it upright. See hauling stone countertops.
• Setting stone on cabinets that are out of level. It will rock, crack or leave gaps.
• Placing a seam across a sink or cooktop opening, where the stone is narrowest.
• Leaving a long overhang unsupported. See standard countertop dimensions.
• Cutting dry. Beyond the health risk, a dry blade overheats and chips the edge.