Not every patch of mold needs a professional. The EPA's long-standing guidance for homes is that if the moldy area is smaller than about 10 square feet, roughly a 3 by 3 foot patch, most homeowners can handle the job themselves. Beyond that size, or when the mold is inside walls, in the air conditioning system, or the result of a flood, the job is better left to people with containment equipment and training.
This guide helps you decide which side of that line your situation falls on, and if it is a DIY job, how to clean it safely.
DIY or professional? A quick guide
| Situation | Usually |
|---|---|
| Under about 10 sq ft on tile, glass, metal, or sealed surfaces | DIY is reasonable |
| Mildew on grout or caulk in a shower | DIY; replace stained caulk |
| More than about 10 sq ft of growth | Professional |
| Mold in drywall, insulation, or inside a wall | Professional |
| Mold in the air conditioning system or ducts | Professional |
| Mold after flooding, sewage, or other contaminated water | Professional |
| Mold that keeps coming back after cleaning | Professional inspection first |
| Anyone in the home has asthma, allergies, or a weakened immune system | Talk to a doctor; consider a professional |
The size rule is a guide, not a promise. A small spot on the face of drywall can be much larger on the back side, and that is the most common way a DIY job turns into a professional one.
Before you start: fix the water
Mold needs moisture. If you clean mold without stopping the water, it comes back. Look for the source first:
- A dripping supply line or drain under a sink
- A leak around a tub, shower, or toilet
- Condensation on windows, cold pipes, or air conditioning lines
- A roof leak or poor attic ventilation
- A clogged air conditioning condensate drain
- High indoor humidity; the EPA recommends keeping it below 60 percent, ideally 30 to 50 percent
Dry anything that got wet within 24 to 48 hours. That window is the difference between a wet spot and a mold problem.
How to clean a small area of mold safely
The EPA's guidance for homeowners comes down to a few rules:
- Protect yourself. Wear an N-95 respirator, long gloves, and goggles without ventilation holes. Avoid touching mold with bare hands.
- Limit the spread. Close the door, open a window if you can, and keep people and pets out of the area.
- Scrub hard surfaces. Use detergent and water on hard surfaces such as tile, glass, metal, and sealed wood, then dry the surface completely.
- Remove porous materials that are moldy. Ceiling tiles, carpet, and other absorbent materials with mold growth may have to be thrown away. Bag them in heavy plastic before carrying them through the house.
- Do not paint or caulk over mold. Paint applied over mold tends to peel, and the growth continues underneath.
- Skip the bleach as a routine step. The EPA does not recommend biocides such as chlorine bleach as a routine part of cleanup, because dead mold can still cause allergic reactions. If you do use a cleaner, never mix bleach with ammonia or other products; the fumes can be toxic.
- Check the result. When you are done, the water problem should be fixed, and there should be no visible mold, no mold-damaged material, and no moldy odor.
Room by room
Bathrooms. Surface mildew on grout, caulk, and painted ceilings is the most common DIY job. Clean it, replace caulk that stays stained, and run the exhaust fan during and for a while after showers. If the drywall behind tile feels soft or the ceiling stain keeps returning, there may be a leak inside the wall.
Basements. Mold on bare concrete or block walls can often be cleaned, but it will return unless water seepage, condensation, and humidity are controlled. Mold on finished basement drywall, carpet, or paneling usually means material has to come out.
Attics. Attic mold usually comes from a roof leak, poor ventilation, or a bathroom fan venting into the attic instead of outside. Fix the cause first. Small spots on roof sheathing can sometimes be cleaned, but heat, tight spaces, insulation, and the size of most attic problems often make it a professional job.
Crawl spaces. Access is tight, moisture is constant, and insulation and wood framing are often involved. Crawl space mold usually needs a professional and a long-term moisture plan, such as a vapor barrier or dehumidification.
Air conditioning and ducts. If you suspect mold in the air handler or ducts, do not run the system, because it can spread spores through the house. This is not a DIY job.
What about black mold?
The color of mold does not identify its species or how risky it is, and the cleanup rules are the same for every kind: small areas on hard surfaces may be cleaned carefully, while larger areas or mold in drywall and insulation should be handled by a professional. Dark mold that has grown into drywall paper after a slow leak usually means the drywall needs to come out, which is a larger job than it looks.
Common DIY mistakes
- Spraying bleach on drywall or wood and calling it done
- Painting over stains without removing the growth
- Cleaning the mold but leaving the leak or humidity problem in place
- Dry-brushing or sanding mold without a respirator, which puts spores in the air
- Running the air conditioning while cleaning a contaminated area
- Opening up a wall to "take a look" and spreading growth that was contained behind it
- Assuming the job is finished when a musty smell remains
When to stop and call a professional
Stop and get help if:
- The area turns out to be larger than about 10 square feet once you start
- You find mold on the back of drywall, inside insulation, or under flooring
- The smell persists after cleaning
- Mold returns within a few weeks
- Anyone in the household develops symptoms or has health concerns
A professional inspection can find hidden growth and the moisture source; see what a mold inspection involves.
What each option costs
DIY cleanup of a small area usually costs little more than a respirator, gloves, goggles, detergent, and trash bags. Professional remediation of a small area typically runs about $500 to $1,500, medium jobs $1,500 to $6,000, and larger ones more, according to HomeGuide's cost data. Our mold remediation cost guide has the full breakdown, and what is mold remediation explains what a professional job includes.
Next step
If the mold in your home is larger than a small patch, inside walls, or keeps coming back, and you own the home, you can call the number on this page to be connected with an independent local mold removal company for an assessment and a written quote.