How To Mount a Sink to Granite

Undermount sinks enhance a granite countertop's beauty.

One of the benefits of a granite kitchen countertop, in addition to its natural beauty, is the ability to attach an undermount sink. Rather than having the sink sit on top of the counter hanging from its rim, the sink is attached to the underside of the stone. The granite is fabricated with a finished rim to allow this attachment. The result is a sink and counter that allows you to push water and debris straight from the counter into the sink, without worrying about this debris getting hung up on the sink's rim. Once the counter has been installed with a cutout for the sink, the sink can be attached with silicone to seal, and epoxy to hold.

Things You'll Need

• Clear silicone caulk
• Epoxy
• 2-by-4 board
• Large C-clamp
• Sink hardware
• Wrench

Instructions

1. Clean the underside of the granite around the sink cutout. The sink's lip extends under the granite by about 1 1/2 inch all the way around. This lip helps hold the sink in place, so this area should be cleared of dust, debris or leftover slurry from the granite's fabrication. Allow time for the water to dry completely; granite is porous and may absorb some water, so clean the area a day ahead of time.

2. Apply clear, silicone caulk around the opening of the sink cutout on the underside of the granite. Remember that the sink's lip extends 1 1/4 inch outward, but the silicone is to help create a watertight seal, so keep the silicone close to the edge. The weight of the sink pushing against it will flatten it out, so there is no need to apply it to the edge, just near it. The bead of caulk should be continuous, all the way around the opening, with no breaks.

3. Place the sink centered directly under the sink cutout, so that the edges of the sink's interior will be flush with the sink cutout. Push the sink into place, so that the silicone caulk flattens, grabs and holds the sink.

4. Place the 2-by-4 board over the opening of the sink, on top of the granite. Make sure there is plenty of space for the board to sit on either side to hold the board firmly in place. Position one end of the C-clamp on top of the board with the other end going into the sink's drain. Fasten the C-clamp on the bottom of the sink and tighten it into place. The C-clamp holds the sink while the silicone begins to harden, and the metal clamps are placed that will permanently fasten the sink to the counter.

5. Attach the sink's hardware to the underside of the granite, using epoxy. Attach the bolt stems of the clamps to the granite, just next to the lip of the sink. by mixing the epoxy and applying it to the counter, and pushing the stem into place. Allow this epoxy to set up for 10 minutes.

6. Attach the clamps to the lip of the sink. The clamps use a nut to screw onto the bolt stem that is attached to the granite. This will hold the sink securely to the granite. Use the epoxy to attach the clamps to the lip of the sink. Follow the sink manufacturer's instructions for where to place these clamps, as each sink's rim may be different. Allow the epoxy and silicone to set up for a full day.

7. Tighten the bolts on the sink's clamps, using a wrench. Remove the 2-by-4 and the clamp.

References

• Ask the Builder: Undermount Kitchen Sinks