How to remove mold from walls safely, and when to call a pro

Step by step: how to remove mold from walls safely, and when to call a pro

Safety first. Wear an N-95 respirator, long gloves and non-vented goggles, and keep children, pets and anyone with asthma or a weak immune system out of the room. If the moldy area is more than about 10 square feet (roughly 3 feet by 3 feet), came from sewage or flood water, or is in your heating and cooling system, the EPA advises getting professional help. Never mix bleach with ammonia, vinegar or other cleaners: the fumes are toxic.

1. 1

   Measure the patch and find the moisture

   Measure the moldy area. Under about 10 square feet, the EPA says most people can clean it themselves; larger than that, stop and call a professional. Then find the water source: a roof or plumbing leak, condensation on a cold outside wall, or a bathroom with no working fan. Mold will come back if the wall stays damp.

2. 2

   Put on your gear and ventilate the room

   Put on an N-95 respirator, long gloves and goggles, plus old clothes you can wash right after. Open a window and set a box fan in it blowing outward, and close the door to the rest of the house. Close the supply vents in that room so spores are not pushed through the ducts.

3. 3

   Protect the floor and furniture

   Pull furniture at least 3 feet away from the wall and lay plastic sheeting or a drop cloth along the base. Take down pictures and curtains on that wall. Fabric that has mold on it goes in a sealed bag to be washed or thrown away.

4. 4

   Mist the mold before you touch it

   Mix about 1 teaspoon of dish detergent into 1 quart of warm water in a spray bottle and lightly mist the patch. Damp mold releases far fewer spores than dry mold. Do not dry-brush it or run a regular vacuum over it.

5. 5

   Scrub with detergent and water

   Dip a soft brush or sponge in a bucket of warm water with a squeeze of dish detergent and scrub the patch in small sections, working from the edges toward the middle. Rinse the sponge in a second bucket of clean water so you do not spread mold around. On painted walls the dark spots should lift within a few passes; a faint shadow left in the paint is usually stain, not live growth.

6. 6

   Wipe with clean water and dry it fast

   Wipe the area with a clean cloth dampened in plain water, then pat it dry with towels. Run a fan or dehumidifier aimed at the wall for several hours. The EPA says materials dried within 24 to 48 hours usually do not grow mold.

7. 7

   Check whether the drywall can stay

   Press the cleaned area with a gloved finger. If the drywall is soft, crumbly, swollen, or the mold has come back through the paint, the growth is inside the board and the section needs to be cut out and replaced. Bare drywall paper and flat, unsealed paint soak up mold the way a sponge soaks up water.

8. 8

   Bag the waste and wash up

   Seal used sponges, cloths and plastic sheeting in heavy trash bags before you carry them through the house. Wash your work clothes on a hot cycle and shower. Wipe the floor under the work area with a damp cloth.

9. 9

   Watch the spot before you repaint

   Check the wall weekly for a month. If it stays clean and dry and the water problem is fixed, prime it with a stain-blocking primer and repaint. Never paint over mold: the CDC notes it keeps growing underneath.

How to clean mold off walls by wall surface

Hard, sealed walls can be scrubbed clean; porous ones often have to be cut out. The EPA’s cleanup guidance says to scrub mold off hard surfaces with detergent and water and dry them completely, and warns that absorbent materials may have to be thrown away because mold fills their pores.

Should you use bleach on moldy walls?

Usually not: detergent and water is the first choice, and bleach is optional for hard, nonporous surfaces only. The EPA’s guide to mold and moisture says killing mold with a biocide such as chlorine bleach is not recommended as a routine practice, because dead mold can still trigger allergies and has to be removed anyway.

If you do use bleach on tile or sealed surfaces, the CDC’s bleach fact sheet calls for no more than 1 cup of household bleach per 1 gallon of water, with windows open. Bleach cannot fix mold growing inside drywall paper, and it can lighten painted walls. Never combine it with ammonia, vinegar or any other cleaner.

Vinegar is a popular home remedy, but it is not part of the EPA or CDC cleanup steps. If you try it, use it on its own, never in the same session as bleach.

When to call a mold professional

Call a professional when the mold is large, hidden, tied to dirty water, or making someone sick. The EPA and CDC point to these situations:

• The moldy area is more than about 10 square feet, or there are several patches across a room.
• The water was sewage or flood water, which brings bacteria as well as mold.
• You smell mustiness but cannot see the source, or the mold is inside the wall cavity, attic or ductwork.
• Your heating and cooling system may be contaminated. Do not run it until it is checked.
• Anyone in the home has asthma, allergies or a weak immune system; the EPA suggests talking to a doctor before cleanup.

You rarely need a mold test first. The EPA says sampling is usually unnecessary when you can see the growth, since there are no federal limits to compare results against. For a related problem in wet rooms, see how to clean shower mold.

How to stop mold coming back on your walls

Keep the wall dry and the air below 60 percent humidity, and mold has nothing to live on. The EPA recommends 30 to 50 percent as the ideal range.

• Run the bathroom fan during showers and for 20 minutes after, and use the range hood when cooking.
• Keep beds and dressers a few inches off outside walls so air can reach the cold surface.
• Use a dehumidifier in basements and check it with a cheap hygrometer.
• Dry any spill or leak within 24 to 48 hours, as the CDC’s cleanup tips advise.
• If the room still smells damp after cleaning, our guide on getting rid of a musty smell covers the next steps.

Mistakes to avoid

• Painting or caulking over mold instead of removing it and fixing the leak first.
• Dry-brushing or vacuuming mold with a regular vacuum, which throws spores into the air.
• Mixing bleach with ammonia, vinegar or another cleaner to make it stronger.
• Scrubbing soft, crumbly drywall over and over instead of cutting out the damaged section.
• Leaving the wall to air dry for days, which gives mold time to grow back.
• Tackling a patch bigger than 10 square feet without professional help.