Caulking around a sink helps keep surface water out of the joint between basin and counter, but sealant does not repair a faucet, drain, or mounting leak. Remove failed material, clean and dry the joint completely, choose a sealant compatible with both surfaces, and apply a thin continuous bead. Respect cure time before getting it wet.
Confirm the joint is the issue rather than another leak
Dry everything and run the faucet while checking underneath. If water comes from supply lines, the drain, or faucet base, repair that first. Caulking the rim can hide an active leak and trap moisture.
Remove old sealant and loose residue
Cut and peel the old bead without scratching the counter or sink. Remove remaining film with a compatible product and let the joint dry. New caulk bonds poorly over grease, soap, old silicone, or moisture.
Apply a continuous bead of the necessary size
Cut a small nozzle opening and work at a steady pace. Tool the bead as the product directs before it skins and remove excess. More caulk does not mean a better joint; an oversized bead can peel and trap dirt.
Respect cure time before exposing it to water
Surface-dry time is not always full cure time. Follow the label for humidity and temperature. If the sink moves when pushed, correct its mounting rather than relying on a flexible bead to hold it in place.