How to Replace a Sink Base Cabinet Floor

Clean up the moldy mess under the sink

The flimsy particleboard bottoms in most kitchen and bathroom sink bases are often swollen and moldy from leaks. The best fix is to cut them out and replace them.

By the DIY experts of The Family Handyman Magazine

Replacing the floor

Let’s face it—it’s easy to get water on the floor of your sink base cabinet. We’ll never understand why cabinetmakers use particleboard for the base, but they do. And once it starts swelling, your only option is to replace it. But you don’t have to cut out the entire bottom. Here’s an easier way to install a new sink base bottom.

Remove the drain lines (and garbage disposer, if there is one) to get maneuvering room. Then trace a cutting line about 3 in. in from all four edges. Then cut out the middle section of the swollen sink base with a jigsaw (Photo 1). Next, cut a piece of 1/2-in. plywood to the interior size of the sink base. Cut slots for the water supply tubes. Seal the edges and face of the plywood with urethane varnish. Then install the new plywood floor and fasten it to the old floor (Photo 2). Caulk around the edges and pipes to prevent water from seeping under the new floor. Finally, reattach the P-trap and garbage disposer.

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Required Tools for this Project

Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.

  • Caulk gun
  • Cordless drill
  • Countersink drill bit
  • Framing square
  • Jigsaw
  • Circular saw
  • Paintbrush
  • Pipe wrench
  • Safety glasses
  • Slip joint pliers
  • Tape measure

Required Materials for this Project

Avoid last-minute shopping trips by having all your materials ready ahead of time. Here's a list.

  • 1/2-in. exterior grade plywood
  • Urethane varnish
  • Caulk
  • 1-1/4-in. galvanized screws