The cabinet under the kitchen sink is dark, closed and full of pipes. When something drips down there, nobody notices until there’s a musty smell, a soft cabinet floor or black spots on the back wall. Mold under the sink is almost always a water problem first and a mold problem second.
Common Causes
- A loose or worn slip nut on the drain trap (the U-shaped pipe)
- Leaking supply lines or shutoff valves
- A worn faucet base or sprayer hose that drips with every use
- Garbage disposal leaks from the seals or body
- Dishwasher drain hose or supply line connections
- Failed caulk around the sink edge letting water run down inside
How to Find the Leak
- Empty the cabinet and dry everything with a towel.
- Lay down dry paper towels on the cabinet floor.
- Run the faucet, use the sprayer, fill and drain the sink, and run the disposal and dishwasher.
- Run a dry paper towel along each connection and watch for wet spots underneath.
Small leaks at slip nuts can often be snugged up by hand. Anything else, like a corroded valve, cracked pipe or leaking disposal, is a job for a plumber.
Cleaning the Cabinet
If the cabinet floor is still solid and the mold is just on the surface, wear gloves and a mask, clean it with soap and water or 3% hydrogen peroxide, and let it dry completely with the doors open and a fan running. See how to remove mold from wood for more.
When the Cabinet Floor Has to Come Out
- The cabinet floor is swollen, soft, crumbling or delaminating (common with particleboard)
- Mold is on the back wall of the cabinet, which is usually your drywall
- The flooring in front of the sink is warped or soft
- The smell stays after you clean
Water often runs under the cabinet base or into the wall behind it, so what you see may be the small part. Also check the dishwasher next to the sink.
Condo Owners: Check Below You
In a condo, a slow kitchen leak can show up as a stain in the unit below. If a neighbor reports one, act fast. Read condo leak from upstairs: who pays?
Free Visual Inspection in South Florida
FL Cleanup offers a free visual inspection with moisture readings and an infrared (thermal) camera to see how far the water spread under and behind your cabinets. We handle licensed mold remediation and drying across South Florida. We answer 24/7, and hablamos español. Call 877-224-2532 or request a free visual inspection online.
About the author: James Rice-Peña is the owner of FL Cleanup and a Florida-licensed Mold Assessor (MRSA4035) and Mold Remediator (MRSR4158). He has worked in property restoration in South Florida since 2012, and FL Cleanup has earned 200+ five-star Google reviews.
