Concrete doesn’t feed mold the way wood or drywall does, but mold can still grow on it. Dust, dirt and moisture on the surface are enough. In Florida, where most homes sit on a concrete slab with concrete block walls, we find mold on concrete under carpet and tile, behind baseboards, in garages and on interior block walls.
Where It Shows Up
- Under carpet and pad after a leak or flood
- Under laminate or vinyl flooring, where moisture gets trapped against the slab
- On block walls behind drywall or furring strips, especially exterior walls
- In garages and laundry rooms with poor ventilation
Mold or Efflorescence?
White, chalky or crystal-like deposits on concrete are often efflorescence, mineral salts left behind when water moves through the concrete. It isn’t mold, but it means moisture is coming through. Mold tends to look fuzzy, spotty or slimy, and comes in black, green, gray or white. See is white mold dangerous? for a side-by-side comparison.
How to Clean Mold Off Concrete
- Wear gloves, eye protection and a mask, and ventilate the area.
- HEPA vacuum loose debris.
- Scrub with a stiff brush and a detergent solution or a cleaner labeled for mold on concrete.
- Wipe or rinse with as little water as possible, then dry thoroughly with fans and dehumidification.
- Only lay new flooring after the slab is confirmed dry. Concrete can feel dry on top while still holding moisture.
Never mix bleach with ammonia, vinegar or other cleaners.
Find Where the Moisture Comes From
- Plumbing leaks: including a slab leak in pipes under the concrete
- Exterior water: poor drainage, sprinklers hitting the walls, or gutters dumping water against the house
- Wind-driven rain coming through block walls, windows or doors
- AC and water heater leaks spreading across the slab
- Past flooding that wasn’t fully dried
Mold on concrete under flooring or behind drywall usually means the materials on top need to come out too. See how to get mold out of carpet and how to remove mold from walls.
Free Visual Inspection in South Florida
FL Cleanup offers a free visual inspection with moisture readings and an infrared (thermal) camera to check slabs, block walls and flooring across South Florida. If mold is confirmed, we handle licensed mold remediation and drying. 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.
