How can I find out if there is mold behind my drywall?

June 8, 2009 9:16 AM

What is the least destructive method I could use to determine what if any mold might be growing in drywall? You see, there's this roof leak...

... that is very minor (the leak only showed up after 5+ days of rain in a row), and that's going to get repaired, but here I am looking at a wall with two pencil thin lines of moisture coming down about a foot and a half. Considering this leak has probably been here since before I moved in, as there is some minor discoloration I just now noticed elsewhere on the wall, I'm a little worried I might have something magical living behind/within the drywall.

I've googled around a bit and while there are several mold remediation companies that are happy to come in and rip out my walls and clean everything out -- no one seems to be in the business of, well, checking if there is anything there to begin with. I admit I'm being cheap and trying to prevent a $1,000+ remediation action without evidence of a problem, but am I just SOL here?

The best I've come up with is hiring a "water leak detection" company. Which is remarkable since I know where the leak is coming from -- the roof -- it's more, well, how leaky is it?

If it helps for anyone's anecdotes, I am in Florida.

posted by cavalier to home & garden (5 answers total)

I've seen home inspectors on TV use a moisture detector on walls to see if there is moisture or to check that mold remediation has been done if there was a known leak/flood. A quick Google search shows that these devices aren't for the general public (they're ~$1000 themselves). I think a home inspector or someone who specializes in mold remediation would have one. (Especially in Florida, where there's probably a lot of flood damage.) And I think they would use their moisture detector before just tearing open your walls, so you wouldn't be stuck paying for a lot of work if it turns out there's nothing there.
posted by LolaGeek at 9:40 AM on June 8, 2009

If the leak is going to be fixed, I don't think you need to worry overmuch about possible mold. Can you smell a moldy or musty smell? Are you experiencing any allergic reactions when you're in the room? If not, you probably don't need to worry about it. There is the concern of having mold that degrades the wood behind the drywall, of course, and not smelling mold won't necessarily mean that there isn't any. I would suggest finding the place on the wall with the most discoloration (i.e. finding where there is likely to be the most wetness behind the wall) and cutting a small hole in the drywall, preferably right over a stud. You can look on the wood and on the insulation paper to see if you can see any mold. Just patching a little hole wouldn't be as difficult as rehanging a whole wall.

Obviously there can be mold present that isn't visible, but mostly if you have a big problem you're going to know about it. A little but of mold isn't a crisis. Also, if you're paranoid, you can take swabs of the wood behind the drywall and send them off to a lab to be tested.
posted by aka burlap at 9:41 AM on June 8, 2009

If there is wet insulation behind the wall, the sheetrock is just the tip of the mold iceberg. You could cut a small square out of the sheetrock, in a place where you can patch it up again, and see/feel/smell the inside of the wall. If wet, moldy, musty, then removal and replacement is the way to go.

However, it sounds like you have a small leak, and not much damage. Let it dry, seal it with pigmented shellac, and paint over it. Watch to see if anything emerges after several months. If no, then you are done with this issue, assuming that the roof repair is good.
posted by Midnight Skulker at 10:27 AM on June 8, 2009

I'm from Florida also (Gainesville) and a few months ago I bought a house with a known mold problem. Here's a few things that I learned that should be relevant:

1) A mold remediation company is not where to go when you want to identify a mold problem. Instead, contact a mold assessment/inspection company. In Gainesville, there's a section dedicated to this in the yellow pages.

2) You're gonna pay a minimum of $250 to get a mold inspection done. That $250 will get you a regular home inspection guy that's taken a basic mold class and is now "certified". That doesn't necessarily mean he knows what he's doing, but it does mean he knows how to take samples and bill you for it. You'll pay much more for a person who actually knows what he's doing (here's an example of a guy who knows what he's doing).

3) Based on what I've learned and experienced, if you stop the moisture ... the mold has no more food to live on. So, theoretically, you stop that water leak and primer over the problem area and you're done.

Sounds like with your problem, if you really want to be thorough, just have the drywall ripped out and then replaced. Would probably be cheaper than getting a mold inspection done. If it were me, I'd just hit it with Kilz.
posted by Dave. at 11:31 AM on June 8, 2009

Hey you guys, thanks!

After paying a CHUNK of money (Talked down from $250, but let's just say it was still healthy..) I got about 8 minutes out of the guy and his moisture detection wand thingamajig, which seemed to be just two prongs which he could press into material and try to pass a current through.

The good news -- everything is dry. All that is there is the original discoloration from getting wet, but even the dark little corner is dry. Roof repair is next week, and assuming there is no more bucket of moisture getting in there, I'm feeling more comfortable with "Dry wall = Dry = No moisture = No mold", at least, no excessive mold. :)

After the repair I will go ahead with Kilz -- unless pigmented shellac would be better? Hmm. I'll check both out. Thank you guys!
posted by cavalier at 10:52 AM on June 12, 2009