How to Install an Undermount Bathroom Sink

An undermount sink mounts beneath the countertop for a seamless look, with no rim sitting above the counter surface. (Not sure if undermount is right for you? See our undermount vs. vessel sink comparison.) Here's what the installation generally involves.

1. Confirm the Countertop Cutout Matches Your Sink

Undermount sinks require a precise cutout in the countertop sized to the sink's basin. This is typically done by the countertop fabricator using a template provided by the sink manufacturer — the cutout needs to happen before the counter is installed on the vanity in most cases.

2. Test-Fit the Sink

Before applying any adhesive, set the sink into the cutout from below to confirm the fit and check the basin sits at the intended depth relative to the counter edge.

3. Apply Mounting Clips or Adhesive

Most undermount sinks use a combination of silicone adhesive and mechanical mounting clips or brackets that pull the sink up snug against the underside of the counter. Follow the sink manufacturer's specific mounting hardware and adhesive type.

4. Seal the Seam

Once secured, run a bead of silicone caulk along the seam where the sink meets the underside of the counter to prevent water intrusion.

5. Let the Adhesive Cure, Then Connect Plumbing

Give the adhesive and caulk the manufacturer's specified cure time before connecting the drain and faucet supply lines and putting the sink into use. See our widespread faucet installation guide for the faucet side.

What to Check Before You Buy

• Confirm your countertop material supports undermount installation (solid surface, quartz, granite, and marble all work well)
• Check the sink's exact dimensions against your planned cutout before ordering
• Factor in professional countertop fabrication if you don't already have a cutout

Browse our sinks and faucets collection to find an undermount sink for your vanity.