Mold behind drywall is the kind you do not see until the wall comes open. The front of the wall can look clean and freshly painted while the back of the drywall, the framing and the insulation have been wet for weeks.
This post covers the signs that point to mold inside a wall, how it gets found without tearing out every room, and why the wall usually has to come open once it is found.
What we saw on a recent job in Simi Valley
This month our crew has been working a mold remediation job in Simi Valley where the problem started at a water heater closet and carried into the bedroom on the other side of the wall. Here is how that job went, in order:
- Readings first. Our team took moisture readings on the closet walls and along the bedroom walls.
- Containment before demolition. Plastic walls with a zippered door went up in the bedroom, with a dehumidifier running inside.
- A second look. A follow-up visit used a thermal camera and more meter readings along the baseboards, and the sections of drywall and baseboard to remove were marked on the photos.
- Opening the wall. The drywall was cut along the bottom of the bedroom walls to expose the framing and insulation, and the carpet was pulled back.
The readings are what decided where to cut, not what the walls looked like from the outside.
Signs of mold behind drywall
You will rarely see the mold itself. What you notice is what it leaves behind:
- A musty smell in one room or one corner that comes back after cleaning.
- Swollen or stained baseboards, or paint that bubbles or peels near the floor.
- A leak on the other side of the wall, such as a water heater, washer, toilet or shower.
- A past leak that was cleaned up but never dried out behind the surface.
- Carpet or pad that stays damp along one wall.
The EPA lists the back side of drywall, the underside of carpet and pad, and the inside of walls around leaking or condensing pipes as common places for hidden mold.
How it gets found without tearing everything out
- Moisture meters show where the wall is wet and how far the wet area runs.
- A thermal camera shows temperature differences across the wall. Wet areas often read cooler. It does not see mold, but it shows where to look.
- A small inspection cut or testing confirms what is behind the surface before the larger cuts are made. Our post on mold remediation costs covers what drives the price once it is confirmed.
Why the wall has to come open
Drywall is paper on both sides of a gypsum core. When the back side stays wet, cleaning the front does nothing about it. The affected drywall is cut out, the framing behind it is cleaned and dried, and new drywall goes in once everything reads dry.
Most cuts are made along the bottom of the wall, because that is where water collects and wicks upward. How high the cut goes depends on the readings. On the Simi Valley job, the sections marked for removal were about 2 feet high.
Why containment goes up first
Cutting into a moldy wall releases dust and spores. Containment keeps that inside the work area instead of spreading it through the house:
- Plastic sheeting walls off the room or the section being worked on.
- A zippered door lets the crew in and out without opening the whole barrier.
- Air filtration equipment cleans the air inside the containment while work goes on.
For more on what happens once mold is found under a floor instead of inside a wall, see our post on mold on a subfloor.
What happens after the wall is open
Finding mold behind drywall is the first half of the job. Here is what usually comes next:
- Remove the affected material. Wet or moldy drywall, baseboard, insulation and carpet pad are bagged inside the containment and taken out.
- Clean the framing. The studs and sheathing behind the wall are HEPA vacuumed and cleaned.
- Dry it. Air movers and dehumidifiers run until the framing reads dry. This is structural drying.
- Check before closing it up. Moisture readings, and clearance testing when it is called for, come before any new drywall goes up.
- Rebuild. New drywall, texture, baseboard and paint. Our construction team handles that part.
On the Simi Valley job, the crew came back after the walls were opened to take readings on the exposed framing inside the containment.
Can you handle it yourself?
Sometimes. The EPA says that if the moldy area is less than about 10 square feet, roughly a 3 by 3 foot patch, most homeowners can handle it themselves. If there was a lot of water damage, or the mold covers more than 10 square feet, the EPA points to its professional mold remediation guidance instead. Mold behind drywall is hard to size up from the outside, which is why readings come first.
FAQ
Can there be mold behind drywall with no visible signs?
Yes. The back of the drywall can be affected while the painted side looks normal. A smell, a known leak nearby, or high moisture readings are usually the first clues.
How much of the wall has to come out?
Enough to get past the wet and affected material. It is decided by readings, not by a set height.
Does painting over it fix it?
No. Paint covers the front of the drywall. The problem is on the back, and it stays there until the source is fixed and the wall is dried or replaced.
What if I live in a condo?
A wall can be shared with a neighbor or the building, which adds another party to the job. Our post on mold in a condo covers how that usually works.
Think there is mold inside a wall?
Total Restoration handles mold remediation and mold after water damage across Ventura County, Santa Barbara County and Santa Clarita. We take readings first, contain the area, and only open what needs to come out. Contact us to set up an inspection.