Mold After Water Damage: How Fast It Grows and What to Do

Quick answer

Dry wet materials within 24 to 48 hours to prevent mold growth (EPA). If mold covers less than about 10 square feet, roughly a 3 ft. by 3 ft. patch, you can usually clean it yourself. If it's bigger, there was a lot of water damage, or sewage was involved, bring in an experienced professional (EPA).

How fast does mold grow after water damage?

The EPA says to clean and dry damp or wet building materials and furnishings within 24 to 48 hours to prevent mold growth (EPA). The CDC gives the same window for drying out a home after a flood (CDC).

Mold can grow on almost anything that stays wet, including wood, paper, carpet, drywall, insulation, wallpaper and upholstery (EPA; CDC). That's why drying starts right away, even before repairs. See how long water damage takes to dry.

Can you clean the mold yourself?

Under about 10 square feet: in most cases you can handle it yourself (EPA).
Over 10 square feet, or a lot of water damage: the EPA points to its professional remediation guidance (EPA).
Sewage or other contaminated water: call a professional with experience cleaning buildings damaged by contaminated water (EPA). See sewage backup cleanup.
Mold in or near the heating and cooling system: don't run it, because it could spread mold through the house (EPA).
Health concerns: talk to a health professional before you start (EPA).

Water still coming in or standing? A local restoration company can start water removal now.

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How do you clean mold off hard surfaces?

Fix the leak first. Cleaning without fixing the moisture problem won't hold (CDC).
Protect yourself. The EPA recommends gloves, goggles without vent holes, and an N-95 respirator, and says not to touch mold with bare hands (EPA).
Scrub hard surfaces with detergent and water, then dry them completely (EPA).
Never mix bleach with ammonia or other cleaners. It produces a poisonous gas (CDC).
Don't paint or caulk over mold. Clean it and dry the surface first. Paint over mold is likely to peel (EPA).

Killing mold isn't enough. Dead mold can still cause allergic reactions in some people, so it has to be removed (EPA).

What has to be thrown out?

Absorbent materials such as ceiling tiles and carpet may have to be thrown away if they get moldy, because mold fills the gaps in porous materials and may be impossible to remove completely (EPA). The CDC also advises removing carpets and upholstery that were soaked and can't be dried right away (CDC).

Moldy drywall is usually cut out rather than cleaned. See when water-damaged drywall can be saved. Photograph anything you throw out for your insurer.

What if it smells musty but you can't see mold?

Mold can smell musty, and the CDC says that if you see or smell mold, you should remove it (CDC). The EPA says to suspect hidden mold when a house smells moldy but you can't find the source, or when there's been water damage and people in the house are having health problems (EPA).

Places the EPA lists for hidden mold (EPA):

The back side of drywall, wallpaper or paneling
The top side of ceiling tiles, and roof materials above them
The underside of carpet and pad
Inside walls around leaking or sweating pipes
Wall surfaces behind furniture, where condensation forms
Inside ductwork

Be careful about opening things up to look. Pulling off wallpaper with mold behind it can release a large amount of spores. If you think you have hidden mold, the EPA suggests considering an experienced professional (EPA).

Do you need a mold test?

Usually not. The CDC does not recommend mold testing. If you see or smell mold, it should be removed, whatever the type (CDC). The EPA says sampling is unnecessary in most cases when mold is visible, and there are no federal limits to compare results against (EPA).

Sampling can help confirm an area was cleaned properly after remediation, and it should be done by someone experienced in mold sampling (EPA).

Does insurance cover mold after water damage?

Often only in a limited way. Many homeowner policies offer limited mold coverage, but only when the mold comes from a covered loss, such as a pipe that suddenly bursts (Washington Office of the Insurance Commissioner). Mold from a slow leak that went on for a long time is a different story.

Ask your agent how your policy handles mold. More detail: does homeowners insurance cover water damage?

How do you keep mold from coming back?

Fix leaks in the roof, walls and plumbing (CDC).
Vent bathrooms and the clothes dryer to the outside, and use exhaust fans while cooking and cleaning (EPA).
Use an air conditioner or dehumidifier to keep humidity down (CDC).
Add insulation to cold surfaces like pipes and exterior walls to cut down on condensation (EPA).
Skip carpet in places that stay damp, like bathrooms and basements (CDC).

Common questions

How soon after a leak does mold start?

The EPA and CDC both say to dry wet materials within 24 to 48 hours to prevent mold growth. After that, porous materials like drywall, carpet pad and insulation are more likely to need removal.

Is a small patch of mold an emergency?

Not usually. If the moldy area is under about 10 square feet, the EPA says most homeowners can clean it themselves. Fix the moisture source first, wear gloves, goggles and an N-95, and scrub hard surfaces with detergent and water.

Should I test to find out what kind of mold it is?

The CDC does not recommend it. You don't need to know the type, because any mold growing indoors should be removed and the moisture problem fixed.

Can I paint over mold?

No. The EPA says to clean up the mold and dry the surface before painting. Paint applied over mold is likely to peel.

Why does my house smell musty when I can't see any mold?

The EPA says a moldy smell with no visible source can mean hidden mold, such as on the back of drywall, under carpet pad, inside walls around leaking pipes or inside ductwork. Opening those areas can release spores, so consider an experienced professional.

Related guides

Local water damage help

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