Overview

This task is about sealing the joint where a kitchen or bathroom sink meets the countertop, plus related seams like a backsplash-to-counter gap, so water can't seep underneath and damage the cabinet or subcounter material. It's a good fit for a homeowner who notices the old caulk line looking cracked, yellowed, or grimy, or who just installed/reset a drop-in or undermount sink and needs to finish the job. It's a small, contained project that takes an afternoon at most.

Tools & materials

  • 100% silicone kitchen & bath sealant with mildewcide (a paintable siliconized-latex/all-purpose caulk is an alternative if you plan to paint over it, but plain silicone holds up better to constant water at a sink)
  • Caulk gun
  • Utility knife or caulk-removal tool
  • Plastic putty knife or razor scraper
  • Isopropyl alcohol or mineral spirits and clean rags
  • Painter's tape
  • Disposable gloves
  • Cup of water or a caulk-smoothing tool for tooling the bead
  • Scrap cardboard or paper to test the bead width before applying

Steps

  1. Clear out anything stored under the sink and put on gloves.
  2. Cut along the existing caulk line with a utility knife, then peel and scrape away all old caulk from both the sink rim and the countertop with a plastic putty knife — leftover residue keeps a sink from sitting flush and creates new gaps for water.
  3. Wipe the entire joint with isopropyl alcohol or mineral spirits and let it dry completely; any dust, grease, or moisture will keep new caulk from bonding.
  4. Apply painter's tape along the countertop and along the sink rim on both sides of the seam, leaving just the gap exposed for clean lines.
  5. Cut the caulk tube tip at a 45-degree angle sized to the gap, load it into the gun, and test the bead on a piece of scrap cardboard first.
  6. Starting at one edge, run a slow, steady, continuous bead of caulk fully around the sink-to-countertop seam (and along any backsplash-to-counter gap you're also sealing).
  7. Smooth the bead immediately with a wet finger or smoothing tool, wiping excess residue off as you go so the line stays even.
  8. Peel the tape away right away while the caulk is still wet to avoid pulling at a skinned-over bead.
  9. Wipe up any smudges with a damp rag and leave the area untouched — no dishes, splashing, or wiping down — for at least 24 hours to let the caulk fully cure.

Safety warnings

  • Ventilate the kitchen or bathroom while working; caulk and adhesive removers give off fumes in a small space.
  • Wear gloves — mineral spirits, alcohol, and uncured silicone can dry out or irritate skin.
  • Keep caulk removers and mineral spirits away from open flames or gas pilot lights, since some are flammable.
  • Utility knives are sharp and this task involves working close to your hands in a tight space — cut away from your fingers.
  • Don't run water, wash dishes, or use the faucet heavily until the caulk has cured per the product label, or you risk washing out an unset bead.

When to call a pro

  • The cabinet or particleboard under the sink is already swollen, soft, or crumbling from a longstanding leak — that's water damage repair, not a caulking fix.
  • An undermount sink has come loose from its clips or mounting adhesive and is sagging or shifting, since that's a structural fastening issue, not just a caulk seal.
  • You have a natural stone countertop (granite, marble, quartzite) and aren't sure which sealant won't stain or discolor the stone.
  • The leak seems to be coming from the plumbing connections or drain fitting underneath rather than the visible caulk line on top.

Cost estimate

$8-$20 for a tube of sealant and basic supplies if you already have a caulk gun

Sources