Mold on Walls: Painted Walls, Drywall and Behind Walls

Mold needs moisture. The EPA calls it the most important factor influencing mold growth indoors. On walls, the water usually comes from one of these:

• Leaks. TDLR lists pipe leaks, roof leaks, floodwaters, sewage back-ups and over-flowing toilets/sinks/bathtubs as common moisture problems.
• Condensation. The EPA says condensation can be a sign of high humidity, and that it can come from high humidity or cold spots in a building. Exterior walls behind furniture, closets and corners with poor airflow are typical spots.
• Steam and cooking. Bathrooms and kitchens without good exhaust. The EPA says to use exhaust fans or open windows whenever cooking, running the dishwasher or dishwashing.
• Floods. In southeast Texas, Hurricane Harvey brought rainfall exceeding 30 inches in many locations in 2017. Walls that sat in floodwater are a different job; see the last section.

If you only clean the stain and don't fix the source, the mold will be back.

A painted wall over plaster, or a wall with a glossy or semi-gloss finish, gives mold a hard surface to sit on. If the patch is small and the paint is intact, it can often be cleaned.

Mold on wall removal, step by step (small patch only):

1. Measure. The EPA says that if the moldy area is less than about 10 square feet (less than roughly a 3 ft. by 3 ft. patch), in most cases you can handle the job yourself.
2. Fix the moisture first. Repair the leak or address the condensation.
3. Wear protective gear. The EPA's minimum for small areas is gloves, an N-95 respirator, and goggles/eye protection. It recommends long gloves that extend to the middle of the forearm and goggles that do not have ventilation holes.
4. Scrub with detergent and water. The EPA says to scrub mold off hard surfaces with detergent and water, and dry completely. If you use bleach, the CDC's limit is no more than 1 cup of household laundry bleach in 1 gallon of water. Never mix bleach with ammonia, vinegar or other cleaners; our vinegar vs bleach for mold guide explains why.
5. Dry completely, then watch the spot.
6. Don't paint over it. The EPA says do not paint or caulk moldy surfaces. Clean and dry first; the EPA notes paint applied over mold tends to peel.

If the stain comes back, or the paint is soft, bubbling or peeling, the mold is probably in the drywall behind it.

Mold on drywall is harder, because drywall is porous: a gypsum core wrapped in paper. Mold that grows into that paper can't be fully scrubbed out.

TDLR, the Texas agency that licenses mold professionals, says mold growth is difficult to clean from absorbent (porous) surfaces such as drywall, carpet, fleecy furnishings and insulation, so those materials should be removed and discarded. It also says that merely applying a chemical such as bleach to drywall, without removing the mold source, is not a permanent effective solution, and that painting over mold is also not an effective solution.

Mold removal on drywall: when it must be cut out

The EPA's remediation tables, written for professionals, are the clearest guide. They describe four cleanup methods: wet vacuum, damp wipe, HEPA vacuum, and discard (EPA remediation guide, chapter 3).

Table: EPA guidelines for wallboard (drywall and gypsum board) with mold growth caused by clean water. Source: EPA Table 2.

Two things stand out. First, the EPA table doesn't list damp wiping for drywall at all, unlike tile, plastic or wood. Second, once drywall mold passes 10 square feet, removal and disposal is on the table. For discarded materials, the EPA says they should be double-bagged using 6-mil polyethylene sheeting.

Wet drywall that hasn't grown mold yet. The EPA's water-damage table says wallboard may be dried in place if there is no obvious swelling and the seams are intact; if not, remove, discard and replace it, and ventilate the wall cavity if possible. That table is for clean water dried within 24 to 48 hours.

Cutting out drywall also disturbs mold. The EPA lists breaking moldy porous materials such as wallboard as an action likely to stir up mold, which is why larger jobs use containment.

Sometimes the wall looks fine, but you smell mold. The EPA says mold may be hidden in places such as the back side of dry wall, wallpaper, or paneling, and inside walls around pipes.

Signs to look for:

• A musty smell near one wall
• Paint bubbling, peeling or staining with no visible mold on the surface
• A known leak inside the wall, like a supply line or shower valve
• Baseboards or drywall that feel soft or damp

Be careful opening things up. The EPA warns that removal of wallpaper can lead to a massive release of spores if mold is growing underneath. Its advice: if you believe that you may have a hidden mold problem, consider hiring an experienced professional. Our guides on mold smell in the house and signs of mold in the house can help you narrow it down.

Mold on wood (studs, trim, paneling, cabinets) is treated a bit differently from drywall. TDLR lists solid wood among the non-porous surfaces that mold can be cleaned from. The EPA's table lists wet vacuum, damp wipe and HEPA vacuum for wood surfaces with small or medium mold areas, and adds removal for large areas.

For wet wood, the EPA's water-damage guidance says to remove moisture immediately and use dehumidifiers, gentle heat, and fans for drying, and that wet paneling should be pried away from wall for drying.

Wood that stays wet can weaken. The EPA notes that molds can weaken floors and walls as the molds feed on wet wood. Soft, crumbling or structural wood should be looked at by a professional.

National cost guide Fixr puts mold remediation for walls at $1,000 to $12,000, with an overall average of $3,500 and a per-square-foot cost of $10 to $30 (updated Aug 2025). Repairs such as new drywall are extra: Fixr says repairing mold damage costs between $75 and $3,000, in addition to the remediation costs. For more, see our mold remediation cost guide.

Call a professional if:

• The area is over about 10 square feet. If there's been a lot of water damage or mold growth covers more than 10 square feet, the EPA points to its professional remediation guidance.
• The water was dirty. If damage was caused by sewage or other contaminated water, the EPA says to call a professional experienced with that kind of damage. That includes most floodwater.
• You suspect it's inside the wall or in the HVAC. The EPA says do not run the HVAC system if you know or suspect that it is contaminated with mold.
• Drywall has to come out and you're not set up for containment.

Texas licensing. TDLR says that in most instances, areas of visible mold less than 25 contiguous square feet in area may be cleaned or removed by people who are not licensed. Larger jobs generally need a licensed mold remediation contractor. The same TDLR sheet says owners or managers of buildings with fewer than 10 dwelling units do not have to be licensed to do mold work on that residential property.

Keep testing and removal separate. Texas law says a license holder may not perform both mold assessment and mold remediation on the same project. If you need to know how far the mold goes, hire a mold testing company first. For the work, hire a separate mold removal company. Find companies in Dallas, Fort Worth or anywhere in Texas, verify the license with our license check, and read how we verify listings.