You can usually clean a small patch of surface mold on a hard, non-porous basement material yourself, as long as the water problem behind it is already fixed. Call a professional when the area is large, when it is in drywall, insulation or carpet, or when the water came from sewage or a source you cannot find.
The rule of thumb that most homeowner guidance uses is a moldy area smaller than about 10 square feet. That is roughly a three-foot by three-foot square. The sections below show how to measure, what changes the answer and how to do the small job safely.
Quick GuideDIY Or Pro: A Decision Table
Match your basement to the closest row. If two rows fit, follow the more cautious one.
| What you see | Likely call | Reason |
|---|---|---|
| Small spots on sealed concrete or a metal shelf | DIY | Hard surfaces clean well and the area is small |
| Under 10 square feet on painted wood framing | DIY with care | Sanding and wiping can work if the wood is solid |
| Fuzzy growth on drywall or paneling | Pro | Porous boards hold mold below the surface |
| Carpet, pad or insulation with growth | Pro | These materials are usually removed, not cleaned |
| Patch larger than about 10 square feet | Pro | More spores are released and containment is needed |
| Water came from a sewer backup | Pro | Contaminated water changes the whole job |
| Mold keeps returning after cleaning | Pro | A hidden moisture source is likely still active |
Measure The Patch Before You Touch It
Lay a tape measure along the longest stretch of visible growth and note the width of the affected band. Multiply the two numbers and add up every separate patch on the same wall or floor. Four patches of three square feet each add up to 12, which is past the usual homeowner line.
Do not stop at what you can see. Pull a loose baseboard corner or look behind a stored box if you can do it without scraping the growth. A small stain on the front of a wall can mean a larger area on the back of it.
MaterialWhat The Mold Is Growing On Decides The Method
Hard, sealed surfaces such as poured concrete, glazed tile and metal can be scrubbed because the growth sits on top. Unfinished wood is in between. Light growth on solid framing can often be cleaned, but wood that is soft, dark all the way through or crumbling is a sign of long-term moisture.
Porous materials are a different story. Drywall, ceiling tile, carpet, cardboard and fiberglass insulation soak up water and the growth goes with it. Wiping the face of a damp drywall panel leaves the rest in place, so these materials are normally cut out and bagged.
Water SourceThe Water Source Matters More Than The Mold
Mold needs moisture to grow. If the cause was a one-time event, such as a dishwasher hose that you replaced last week, the cleanup is a bounded job. If the cause is a seeping wall, a failed window well or a cracked drain line, scrubbing is only a short pause.
Sewage is the clear exception. Water from a backed-up drain carries bacteria, and it calls for protective gear and disposal steps that go beyond a mold cleaner. A crew that handles flood damage restoration will treat it as a contaminated loss from the start.
Commerce City Basements And The Ten Square Foot Rule
The EPA guide to mold, moisture and your home states that no mold grows without water or moisture. It also says that if mold is present you must clean it up and fix the water problem. For a Commerce City basement, that means a dehumidifier or a bleach bottle is never the whole answer, so trace the damp before you spend a weekend scrubbing.
The same guide uses a rule of thumb of less than about 10 square feet for an area a homeowner might clean, and it points larger areas and heavy water damage toward remediation guidance. Treat that number as a ceiling and not a target, and call a crew if the patch is close to it.
Unsure If It Is Over The Line?
Call the 24/7 line and describe the size, the material and the water source.
How To Do The Small Job Safely
A small cleanup is still worth doing in order. This is a reasonable sequence for a patch on a hard surface.
- Fix the water source first and let the area dry. Cleaning damp surfaces invites the growth back.
- Wear an N95 or better respirator, goggles and rubber gloves, and open a window or run a fan that blows outside.
- Cover nearby items with plastic and keep children and pets out of the basement while you work.
- Lightly mist the surface so growth does not become airborne, then scrub with detergent and water and wipe with clean rags.
- Bag the rags and any removed material, tie the bag and put it in the trash. Dry the surface fully with a fan.
- Recheck the spot every week for a month. New growth means moisture is still reaching it.
Signs You Should Stop And Call A Pro
Put the sponge down if the smell is strong and you cannot find the source. Stop too if you find growth inside a wall cavity, under flooring or on the underside of a stair. These are signs that the visible patch is the edge of a bigger problem.
A pro job follows a written plan with containment and air filtration, which the homeowner version cannot match. If you hire help, the EPA guide suggests choosing a contractor with mold cleanup experience and checking references. See the mold remediation page for what that service covers.
Nearby TownsSame Question Across The Metro
Basements in Denver, Thornton and the rest of the metro raise the same questions, because the decision depends on size, material and water and not on the zip code. Measure first, then match your basement to the table above.
FAQCommon Questions
How big is too big for DIY basement mold cleanup?
A common rule of thumb is a moldy area smaller than about 10 square feet. Larger areas, or mold on porous materials such as drywall and carpet, are usually better left to a crew.
Can I just paint over basement mold?
No. Paint does not remove growth, and the moisture underneath can peel the new coat. Clean or remove the affected material, fix the water source and let the surface dry before you paint.
Is bleach the right cleaner for basement mold?
On hard surfaces, detergent and water with careful scrubbing removes growth. Bleach does not reach into porous materials, and it should never be mixed with ammonia or other cleaners.
Should I test the mold before cleaning it?
Testing rarely changes the next step. Whatever the type, visible growth needs to be cleaned or removed and the moisture fixed. Ask a contractor if you want testing for a specific reason.
Does my insurance pay for basement mold?
It depends on the cause of the water and your policy wording. Check your policy and ask your insurer before cleanup, and keep photos and receipts.
My Commerce City basement smells musty but I see nothing. What now?
A musty smell means moisture is probably present behind a surface. Check for damp spots at the base of walls, then look for a leaking window well or pipe, and call a crew if you cannot find it. Starting with the water source, as the EPA guide advises, saves repeat cleanups.
Water still spreading? Call (303) 952-8295 and a crew can be dispatched the same day when available.