Resealing an undermount sink is an important maintenance task that will extend the life of your sink and prevent leaks. With some basic supplies and a bit of time, resealing an undermount sink is a DIY project most homeowners can tackle. Here is a step-by-step guide on how to properly reseal an undermount sink.

Gather the Necessary Supplies

Before starting the project, you’ll need to gather a few key supplies:

  • Silicone caulk – Specifically look for 100% silicone caulk that is mold and mildew resistant. Make sure the caulk is designed for kitchen and bath applications.
  • Caulk gun – This will make applying the caulk much easier. Get an adjustable ratchet gun that can accommodate 10 oz silicone tubes.
  • Cleaning solutions – You’ll need household cleaners like rubbing alcohol, acetone, or denatured alcohol to thoroughly clean the underside of the countertop and sink rim before applying new caulk.
  • Rags – Have some lint-free cloths or paper towels on hand to clean the area.
  • Utility knife – A sharp blade will help scrape off old caulk.
  • Masking tape – Help get crisp caulk lines by masking areas off.
  • Drop cloths – Protect surrounding surfaces from drips.

Prepare the Sink Area

Before resealing, you’ll need to adequately prepare the area:

  • Clear everything out from under the sink and give the area a thorough cleaning. Remove any items on the countertops directly around the sink as well.
  • Using a utility knife, carefully scrape out the old caulk. Be sure to get all of the old caulk completely removed. Wipe away any debris.
  • Clean the underside of the countertop rim and the top of the sink with rubbing alcohol, acetone, or another degreasing solution. The area must be completely clean and dry for the new caulk to adhere properly.

Apply New Silicone Caulk

Once prepped, it’s time to apply the new caulk:

  • Load the caulk gun with a fresh tube of 100% silicone caulk. Cut the tip at a 45-degree angle for easier application.
  • Mask off the sides of the countertop and sink edges with painter’s tape for clean caulk lines.
  • Hold the caulk gun at a consistent 45-degree angle and neatly apply the caulk around the entire perimeter where the sink meets the countertop.
  • After going around the entire sink, use a dampened finger, cloth, or shaping tool to smooth the caulk evenly and get a consistent seal. Remove any excess.
  • Spray the newly caulked area lightly with rubbing alcohol to help speed up drying.
  • Allow the caulk to fully cure for at least 24 hours before using the sink. The caulk seal should not come into contact with water during this time.

Tips for a Professional Look

Follow these tips for a resealing job that looks seamless:

  • Take your time applying the caulk slowly and smoothly in a consistent bead. Don’t rush.
  • Keep your caulking work area clean and dust-free.
  • Maintain a steady angle with the caulk gun for the most uniform application.
  • For kitchen sinks, use a white or almond colored caulk to best match the countertops.
  • Make the caulk lines slightly convex for optimal drainage.
  • Use painters tape for the sharpest caulk lines and easiest clean up.
  • Dampen your finger before smoothing out the caulk for easy spreading.
  • Wipe away any excess caulk with a damp paper towel before it dries.

FAQs About Resealing an Undermount Sink

How often should the caulk around an undermount sink be replaced?

It’s best to reseal the caulk around an undermount sink every 1-2 years. Signs it may need replacing sooner include cracks, excessive shrinking, mold, and any water leaks.

What’s the ideal caulk thickness when resealing a sink?

Aim for a caulk bead with a thickness of 1/4″ to 3/8″ around the sink perimeter. This will provide good adhesion and flexibility.

Is 100% silicone the best caulk for undermount sinks?
It is! 100% silicone is waterproof, mold-resistant, and durable for the constant moisture under a sink. Do not use latex caulk.

Can I use the sink right after resealing?

No, allow the caulk seal to fully cure for at least 24 hours before use. The caulk requires this time to adhere completely and become water resistant.

Should I caulk the drain when resealing a sink?

No, you should not apply caulk around the drain opening. This area requires plumber’s putty and maintenance when installing the drain basket.

Why is my new caulk seal cracking around the sink?

This can happen is the area wasn’t cleaned properly before applying the caulk. Grease, moisture or soap residue prevents caulk from properly adhering and leads to cracks.


Resealing the caulk around an undermount sink is a project any DIYer can tackle with minimal supplies. Just be sure to thoroughly clean and prep the area first, take your time applying a smooth uniform bead of 100% silicone caulk, and allow proper drying time. Follow the steps outlined and your sink will be sealed and protected from leaks for years to come. Be diligent about resealing every 1-2 years before cracks appear to prevent water damage under the sink. With a little time and effort, you can keep your undermount sink looking and functioning like new.