Mold doesn't always show itself. When a pipe drips inside a wall or rainwater finds its way behind siding, mold can grow on the back of drywall for a long time before you see anything. Here's what to know, based on guidance from the CDC and EPA, and the signs worth paying attention to.
Is hidden mold harmful?
According to the CDC, exposure to damp and moldy environments can cause a range of health effects, or none at all, depending on the person. Common reactions include stuffy nose, wheezing, and red or itchy eyes or skin. People with allergies, asthma or weakened immune systems can be more sensitive. The EPA advises that indoor mold growth should be addressed and that the key to mold control is moisture control.
Mold also damages the home. It feeds on the paper face of drywall, wood framing and other organic materials. Over time, it can stain and weaken them, and the musty smell can be hard to get rid of until the source is removed.
Signs of mold behind drywall
- A musty, earthy smell that's stronger in one room or closet, or after rain.
- Stains or discoloration, often yellow, brown or gray, that come back after painting.
- Bubbling, peeling or cracking paint in one area.
- Soft, warped or bulging drywall.
- Baseboards that are swelling or caulk lines that stay dark.
- A known leak in the past, like an overflowing tub upstairs, a leaky window or a roof leak.
- Allergy-like symptoms that seem to ease when you leave the house.
Common causes in DC-area homes
- Humid summers and basements below grade in Montgomery County and Northern Virginia.
- Older rowhouse plumbing and radiator lines in DC.
- Bathrooms with weak or no exhaust fans.
- Window and door flashing leaks after heavy rain.
- Condensation on cold exterior walls behind furniture.
- HVAC condensate lines and water heater leaks.
What to do if you suspect mold
1. Find and fix the moisture source
Cleaning without fixing the water problem means the mold comes back. Leaks, drainage and humidity come first. Aim to keep indoor humidity below about 50 to 60 percent, as the EPA suggests.
2. Don't just paint over it
Paint and stain-blocker can hide the color but won't fix wet drywall or growth behind the surface. If drywall has been wet, it often needs to be cut out and replaced.
3. Know the size
The EPA notes that a moldy area less than about 10 square feet can often be handled as a smaller cleanup, while larger areas, HVAC contamination or damage from sewage or contaminated water call for experienced professionals. If you have health concerns, talk to your doctor.
4. Protect yourself
Anyone handling moldy materials should avoid breathing in dust and spores, using gloves, eye protection and an appropriate respirator such as an N-95, and keep the work area contained.
5. Repair properly
Once dry and clean, the wall is rebuilt: new drywall, mold-resistant materials in damp areas, primer, paint and better ventilation.
Prevention: the best fix
Because mold needs moisture, prevention is mostly about water. Run bathroom exhaust fans during showers and for a while after. Use a dehumidifier in basements during humid DC summers. Keep gutters clean and downspouts directing water away from the foundation. Check under sinks, around toilets and near the water heater a few times a year. Re-caulk tubs, showers and windows when caulk cracks or pulls away. Leave a small gap between large furniture and cold exterior walls so air can circulate. If you have a leak, dry wet materials quickly; the EPA notes that drying water-damaged areas within 24 to 48 hours helps prevent mold growth.
Should you test for mold?
The CDC and EPA generally don't recommend routine sampling to identify the type of mold, because visible growth and a musty smell already tell you there's a problem to fix, and there are no federal standards for acceptable mold levels. Testing can be useful in specific situations, such as real estate transactions or when hidden growth is suspected but not found.
How we help
We handle small-area mold cleanup, fixing the moisture source where it's within handyman scope, and rebuilding the wall afterward, with larger jobs referred to certified partners. Learn more on our mold remediation page, and see drywall and plaster repair for the rebuild. Also read when to patch drywall yourself. Text photos to (202) 438-6197.