How Fast Does Mold Grow? 24 to 48 Hours, $1,100 to $3,400

Mold timing from the EPA; drying time from HomeAdvisor. No agency publishes an hour-by-hour mold clock, so this table stops where the sources stop.

When to call: the 24 to 48 hour warning signs

• Call now: wet drywall, carpet or insulation that has been wet since yesterday, sewage or floodwater anywhere, or a musty smell that was not there before.
• Today: any wet material you cannot dry on your own within the EPA's 24 to 48 hour window.
• Can wait: a small spill on a hard floor that you dried right away.

How fast does mold grow after water damage?

The EPA's answer is a window, not a single hour: dry water-damaged areas and items within 24 to 48 hours to prevent mold growth, and in most cases mold will not grow if wet materials are dried in that time. Past that, mold can grow on anything that stayed wet, often where you cannot see it, such as the back of drywall, under carpet pad and inside wall cavities.

Some sites publish an hour-by-hour mold clock with cost multipliers for each stage. We did not find an agency or a national cost guide that publishes one, so we do not. The timer above counts from your start time against the EPA's 24 to 48 hour window and nothing else.

Why the clock matters for the bill

Speed changes which line items show up on the estimate. HomeAdvisor prices extraction and drying at $3 to $4 per square foot for clean water and $7 to $7.50 for black water, and R&R Magazine says clean water can turn into Category 2 or 3 if it sits. Mold adds its own line: HomeAdvisor lists mold removal within a water job at $1,100 to $3,400, averaging $2,225. A standalone mold job averages $2,368 in HomeAdvisor's mold guide.

Run your own numbers in the water damage cost calculator, or read the water damage restoration cost guide for every guide's figures.

Mold after water damage: how to tell

• A musty smell. The EPA says to suspect hidden mold if a room smells moldy but you cannot see the source.
• Spots or staining on drywall, baseboards, or the underside of carpet.
• Drywall that stays soft or cool to the touch days after the water stopped.
• Warped flooring or a subfloor that never fully dried.

For the full job, read mold remediation cost and mold inspection. For basements and crawl spaces, see basement flooding and crawl space mold.

Can I clean the mold myself?

Sometimes. The EPA says a homeowner can generally handle an area under about 10 square feet. Larger areas, or mold after a lot of water damage, call for a pro. The EPA also says not to paint or caulk over mold, and to fix the water problem first or the mold comes back.

Does insurance cover mold after water damage?

It depends on the water. The Texas Department of Insurance says most policies cover sudden and accidental water damage but most do not cover gradual leaks or the mold that comes with them. Photograph everything before cleanup, call your insurer early, and never sign over the claim to a contractor.

How the call works: how calls work. In states that license mold work, ask for the license number.

What to do right now to beat the clock

1. Stop the water at its source.
2. Write down when it started; that is the time the EPA's window counts from.
3. Photograph every wet room before moving anything.
4. Pull wet rugs and furniture off the floor and open windows if the outside air is dry.
5. Call for extraction and drying if materials will still be wet tomorrow.
6. Call your insurer if you plan to claim it.