How to Reseal an Undermount Sink

By
Lee Wallender
Lee Wallender
Lee Wallender

Lee has over two decades of hands-on experience remodeling, fixing, and improving homes, and has been providing home improvement advice for over 13 years.

Learn more about The Spruce's Editorial Process
Updated on 07/20/23
Reviewed by
Deane Biermeier
Deane Biermeier
Reviewed by Deane Biermeier
Deane Biermeier is an expert contractor with nearly 30 years of experience in all types of home repair, maintenance, and remodeling. He is a certified lead carpenter and also holds a certification from the EPA. Deane is a member of The Spruce's Home Improvement Review Board.
Learn more about The Spruce's Review Board
Undermount Stainless Steel Kitchen Sink and Tile Counter
Image Source / Getty Images
In This Article
Project Overview
  • Total Time: 1 hr - 1 hr, 30 mins
  • Yield: Reseal undermount sink
  • Estimated Cost: $10 to $15

Whether you installed the undermount kitchen sink yourself or had it installed by a pro, it's not uncommon for the bond between the sink and the bottom of the countertop to pull away. The break in the bond doesn't usually result in flooding below the cabinet since it's located at the very top. But small leaks will happen, and it's never good for an undermount sink to have a poor bond.

Resealing an undermount kitchen sink is a do-it-yourself job that can be done in about an hour.

The 11 Best Kitchen Sinks of 2024

Before You Begin

Drop-in sinks (also called self-rimming) drop in from the top and hang via the rim of the sink. Undermount sinks are secured beneath the cutout opening in the countertop, hanging from the bottom of the countertop.

Adding new sealant on top of old sealant may not help since the undermount sink clamps may need to be re-tightened. The best solution is to entirely remove the sink, clean the sink and countertop surfaces, and then re-seal and clamp the sink to the countertop.

Why Sinks Become Unsealed and Their Solutions

Understand the most common causes for undermount kitchen sinks losing their seal, along with tips for how to fix the problem when you reseal the sink:

  • Poorly prepared surfaces: The bottom of the countertop (where it contacts the sink) may not have been cleaned thoroughly. Dust on granite or solid-surface such as Silestone can weaken the bond and should be cleaned up before installation. When you re-seal the sink, be sure to use denatured alcohol to clean off all surfaces prior to caulking.
  • Insecure clamps: The clamps or the epoxy, or both, used to secure the sink to the bottom of the countertop were loose enough to cause the caulk to quickly pull away. Tighten the clamps thoroughly.
  • Wrong sink sealant: The sink installer may have failed to use the correct kitchen sealant. If an ordinary caulk was used to seal the sink, it likely will fail quickly. Most undermount sink manufacturers recommend that you use pure, 100-percent silicone sealant for undermount sink installation.
  • Age and usage: Even perfectly installed undermount sinks can fail after enough time and use. The silicone sealant dries out and the clamps start to loosen due to constant vibrations on the counter and the weight of the sink.

Safety Considerations

Be careful when lifting and holding the undermount sink. Wear safety glasses when using the denatured alcohol, especially when working under the countertop.

What You'll Need

Equipment / Tools

  • Electric drill and driver bits
  • Putty knife
  • Rags
  • Safety glasses

Materials

  • 100-percent silicone kitchen sealant
  • Replacement undermount sink clips
  • Denatured alcohol
  • Bucket
  • Old towels

Instructions

  1. Prepare the Work Area

    Clear out all items from below the sink. Place a towel on the floor of the sink cabinet for better comfort. The outer edge of the cabinet floor is sharp and uncomfortable to lay on, so drape a thick towel or soft bath mat over it.

  2. Turn Off the Water

    Shut off the water to the sink under the sink cabinet. Be sure to turn off both controls.

  3. Remove Fixtures and Connections

    Remove all of the plumbing supply and drain pipes and let the water drain into a bucket.

  4. Remove the Sink

    Unclamp the undermount sink from the countertop. If the silicone caulk is old enough and has been failing, it should be relatively easy to pull the sink away from the countertop.

  5. Scrape Off Sealant

    With the sink removed, scrape off all of the caulk or sealant from the top rim of the sink. The surface should be smooth. Follow by scraping off any remaining sealant from the bottom of the countertop.

  6. Clean the Sink Rim and Countertop

    Clean the surfaces thoroughly with denatured alcohol. Clean both the sink rim and the bottom of the countertop.

  7. Apply Silicone Sealant

    With the joint clean and dry, apply a thin bead of the recommended silicone sealant to the top flange of the sink.

  8. Install the Undermount Sink

    Re-install the sink quickly, before the silicone sealant cures. Clamp into place.

  9. Clean Off Sealant

    With a clean rag, wipe away any sealant that may have seeped through either side of the sink.

When to Call a Professional

Resealing and installing an undermount sink can be difficult because you need to simultaneously hold the sink in place while mounting it, all within tight quarters. Plumbers and countertop technicians are familiar with this project and can help.