How do you seal an undermount sink?
How to Seal an Undermount Sink Step 1 – Prepare the Countertop. If this is a new installation, start with the countertop turned upside down on a sturdy surface. Step 2 – Apply Sealant. Apply a steady bead of silicone around the edge of the countertop (if new install) or around the juncture between the counter and sink (if existing). Step 3 – Clean Up.