The One Big Drawback to Undermount Sinks

updated Jul 17, 2020
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(Image credit: Minette Hand)

Undermount sinks are often a no-brainer decision when remodeling a kitchen. There’s lots to love: they look nice, let you to wipe water and crumbs directly from the counter into the sink with a single swipe, and they eliminate that gunk-magnet seam around the lip of overmount sinks. With all these pros, what’s the catch?

The one big drawback to undermount sinks is that water can get in between the sink and the counter, causing mold problems — especially with countertop materials that are not water resistant. Proper knowledge, installation, and maintenance can keep these problems at bay.

First off, there are multiple ways to install undermount sinks, so read up on the different options and decide which is best for you. Here’s a quick overview:

  • Positive reveal: The edge of the countertop stops before the sink bowl, leaving part of the sink rim exposed. This install requires less precision, but large reveals create a small “ledge” that food can land on instead of falling directly into the sink.
  • Negative reveal: The edge of the countertop overhangs the sink walls. This looks more streamlined, and leaves to no little ledge for food bits, but the countertop edge is more susceptible to chips. It can also hide any mold and mildew growing underneath the countertop edge.
  • Flush mounted: Seen with the sink below, the edge of the countertop and the edge of the sink bowl stop at the same point, so the edges align. This requires the most precision and skill during installation, but is easiest to clean.
(Image credit: Minette Hand)

Proper Sink Installation

The first line of defense? Make sure that your undermount sink is correctly installed. You, or your installer, should clean the area with denatured alcohol prior getting started. Then, form an initial seal by applying an adhesive (usually a two-part epoxy but sometimes silicone) to the sink before attaching it to the underside of the counter. Then seal the gap with silicone caulk. Look for mold-free or mildew-resistant caulk designed for kitchens and baths.

Proper Countertop Sealing

When you have a negative reveal, a portion of the countertop underside is exposed to splashing water. When you use a porous material, water can seep through and the sink area can become a breeding ground for mold. If you do use something like natural stone or butcherblock, make sure the countertop is sealed on all sides. Or, opt for a non-porous countertop when designing your kitchen.

(Image credit: Minette Hand)

Cleaning & Maintenance

If you have an undermount sink, regularly clean and dry the silicone caulking between your sink and your counter. Check for cracking or moldy caulk, and replace if you see an issue. If you do this yourself, you’ll need to thoroughly remove the old silicone and recaulk, allowing sufficient time to dry.

Of course, you can always eschew the undermount in favor of an integrated sink, which is easier to clean (albeit more expensive).

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