Mold
How to remove mold from walls
By ARO Restorations · Updated
Short answer
For a small patch on a painted or hard wall, wear gloves, eye protection and a well-fitting N95 respirator and wash it with water and dish detergent, then dry it. If the mold is inside the drywall, keeps returning or covers a large area, the affected section needs to be removed under containment.
In this guide
First, decide whether it is a surface problem
Mold on a wall comes in two kinds, and the method depends on which you have.
Surface growth sits on paint, tile or sealed surfaces, usually because of condensation or humidity. Bathroom ceilings, corners behind furniture and window surrounds are typical. It wipes off.
Growth in the material has taken hold in the paper face of drywall, often on both sides, because the wall got wet from a leak or flood. The surface may look only slightly stained while the back is covered. It does not wipe off, and the wall section has to come out.
Clues that it is in the material: the drywall is soft or crumbly, the stain reappears soon after cleaning, there was a known leak, or the baseboard is swollen.
How much is too much to do yourself
Health Canada treats mold as a small amount when there are three or fewer patches with a total area under one square metre. That can generally be cleaned by a homeowner. For a patch larger than three square metres, mold that returns after cleaning, or mold hidden inside walls or ceilings, Health Canada advises hiring a professional.
Cleaning a small patch, step by step
- Protect yourself. Rubber gloves, safety glasses or goggles, and a well-fitting N95 respirator.
- Protect the room. Close the door, open a window, and keep children, pets and anyone with asthma away.
- Do not dry-brush. Lightly dampen the area first so that spores are not released.
- Wash. Use water and dish detergent with a cloth or sponge. Work from the outside of the patch inward.
- Rinse with a clean damp cloth.
- Dry thoroughly. Use a fan pointed out of the room or a dehumidifier.
- Bag the cloths and dispose of them. Wash your clothes separately.
By wall type
Painted drywall. Surface mold on sound paint cleans as above. If the paint is bubbling or the board is soft, the board is wet inside.
Bare drywall. Paper-faced board with visible growth should be replaced, not cleaned.
Concrete and block. Scrub with detergent and water and a stiff brush. Concrete does not feed mold, so growth there is living on dust or paint, and points to dampness in the wall.
Wood panelling and trim. Clean the surface, then check behind it. Growth on the back means the wall cavity is damp.
Tile and grout. Clean with detergent. Stained caulking usually has to be cut out and replaced.
Why bleach is not the answer
Bleach can lighten a stain on a hard, non-porous surface. On drywall and wood it does not reach growth below the surface, and the water in it adds moisture. It also does nothing about the cause.
Fix the cause, or do it again
- Bathroom: run an exhaust fan that vents outdoors during and after showers
- Corners and closets on exterior walls: move furniture a little away from the wall and improve air circulation
- Windows: reduce indoor humidity in winter and wipe condensation
- Basement walls: run a dehumidifier, and look for seepage
- Any leak: repair it and dry the wall within a day or two
When to call a professional
- The affected area is more than a few square metres in total
- The mold is inside the wall or has come back after cleaning
- The cause was a flood, sewage or a long-term leak
- Someone in the home has asthma, allergies or a weakened immune system
After cleaning: watch the spot
Mark the date and check the area every week or two for a couple of months. If it stays clean, the cause was dealt with. If it returns, the moisture is still there, and the next step is finding it, not cleaning again.
More: mold removal and remediation.
Questions people ask
What kills mold on walls?
Washing with water and dish detergent removes surface mold from painted and hard walls. The key step is removal and drying, plus fixing the moisture. On porous materials such as bare drywall, the affected section should be replaced.
Can I paint over mold on a wall?
No. Mold grows through ordinary paint. Clean or remove it first, fix the moisture, let the wall dry fully, and then repaint.
Should I use bleach or vinegar on mold?
Neither is needed for a small patch. Health Canada recommends water and dish detergent. Bleach does not penetrate porous materials and does not fix the cause.
How do I know if mold is inside the wall?
Soft or crumbling drywall, staining that returns after cleaning, a swollen baseboard, a musty smell or a known leak all suggest growth inside. A moisture meter reading helps confirm it.
Is it safe to remove mold myself?
For a small amount, with gloves, eye protection and a well-fitting N95 respirator, yes. People with asthma, allergies or weakened immune systems should not do the cleaning.