Kitchens and bathrooms have a variety of different sink installations, such as drop-in sinks. Many homeowners prefer the undermount sink installation, however, since its hidden rim beneath the counter top allows all the surrounding surfaces to be easily cleaned. Securing the undermount sink to the counter can be done in two different ways: by attaching it to a new counter top while it is upside down or installing it from beneath the sink cut-out.
Position the new counter top in an upside-down orientation across the cabinetry that it will reside on. The counter top should already have a sink cut-out ready for installation.
Squeeze silicone caulk onto the rim of the undermount sink. Make sure that a generous amount covers the rim; any excess caulk can be removed with a rag after installation.
Turn the sink over and position it evenly across the cut-out on the counter top.
Place a self-tapping screw into one of the sink's screw holes. Turn the screw with a screwdriver to secure it to the sink and counter top. Do not fully tighten.
Repeat Step 4 for the remaining screws around the sink. Each sink manufacturer has a different number of screws. Consult the owner's manual for exact screw numbers.
Tighten the screws slightly with the screwdriver using a diagonal approach; tighten one screw slightly and then move across to the screw that is diagonal from the previous one and slightly tighten that one. Continue this diagonal approach with all the screws until the sink is fully tightened.
Turn the counter top and sink configuration over. Inspect the sink and counter connection. Wipe away any excess caulk with a rag.
Repeat Step 2 from Section 1.
Lay down under the counter top's empty sink cut-out. Press the undermount sink to the counter top from below. Ask a friend to verify the sink's centering from above the counter top.
Lay a two-by-four across the sink from above. Make sure that the friend places the wood length so that the sink can still be held from below since the caulk has not fully dried yet.
Attach a bar clamp to the two-by-four and the drain hole at the bottom of the sink. Tighten the clamp slightly. The helper should perform this step so that the person under the counter top can still hold the sink.
Inspect the sink from above for proper centering. Completely tighten the bar clamp at this point. The sink no longer needs to be held from below.
Attach bolt posts underneath the counter top next to the sink's rim with two-part epoxy. There should be at least two bolt posts glued across from one another, but each sink manufacturer has different configurations. Consult the sink's manual for specific bolt post positioning. Allow the epoxy to dry for a minimum of 10 minutes.
Place a sink holder hardware piece onto one bolt post. Place a washer and wing nut on the same bolt post. Tighten the wing nut slightly. Make sure that the holder is pressing against the sink's rim.
Repeat Step 7 for the remaining bolt posts.
Tighten the wing nuts fully using the diagonal approach. Allow to dry before attaching plumbing and using the sink. Remove the bar clamp and two-by-four from the top of the sink.
Things You Will Need
2-by-4-inch wood length
Sink holder hardware