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Mold beneath bathroom window . How do we rectify it?

16 years ago

I just removed vinyl wallpaper in one of our bathrooms and found mold in an area underneath the window down into the drywall and the studs. This was also the case 11 years ago when we moved in. We've never seen evidence of a leak. When we moved in, we just figured the previous owners had left the window open and it rained in, so we replaced the drywall and wallpapered, but now it's happened again. I called a few window people thinking the window must be leaking, and the 2 or 3 I talked to on the phone felt sure it caused by condensation.

Does that sound correct, and what do we need to do to correct the situation to so it won't happen again? We thought we'd have it recaulked on the outside, and add some "Great Stuff" foam sealant in a small gap in the framing underneath the window. We'll also clean up the mold and replace the drywall with cement board and have our kids always use the exhaust fan while showering. Does that sound like it would fix the problem, or should we have the window replaced or something else?

Thank you so much for your expertise and help!

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Comments (8)

ron6519
16 years ago
Mold grows in damp areas. The bath is a damp area. There doesn't need to be a leak. You need to have a good exhaust fan and use it effectively. Even then mold can grow in areas of low air movement, such as corners. Open seams in wallpaper will be a breeding ground for mold.
A simple solution of chlorox and water will kill mold or you can buy one of the products they make.
Ron
karoloke
Original Author
16 years ago
Thanks, Ron. We didn't have mold anywhere else on the wallpaper except in area below the window and up the sides a little bit, even though we did have a lot of open seams in the wallpaper. We had a guy come and check the caulking on the outside and he couldn't see a leak anywhere, but we could see a water stain on the under side of the sill when we removed it. If we just treat the mold and repair the wall, is that enough to keep it from returning (if we use the exhaust fan religiously)?
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ron6519
16 years ago
While the sill is off, take the hose and simulate a rain event against the window. If it's leaking, this should show you where it's coming in. This might take awhile depending on the opening.
Ron
karoloke
Original Author
16 years ago
Thanks for the good suggestion. We hosed it off for several minutes at different angles and didn't see any evidence of leaking. I wished we could have gotten right smack in front of the window when we sprayed it but it is a second story window. We did stand on a step ladder, though. It must just be from condensation, I guess. I just hope the problem won't come back.
Michael
16 years ago
The mold will return as long as there is heavy condensation on the window. Try opening the top sash of the window an inch when using the shower. Or, wipe down the condensation when done showering or when you see condensation.

I bet the window has a metal spacer.

Michael
karoloke
Original Author
16 years ago
Thanks for your response, Michael. What is a metal spacer, and why would you guess our window has one?

We noticed one spot around the metal frame of the window where the insulating sealant has been knocked out a little bit and it feels much warmer there when the sun shines in. (I don't mean warmer to the touch, but when I hold my hand about an inch away from the frame in that spot I can feel more heat coming in). Could that be part of the problem? We had a good heavy rain today and saw no leak.
Michael
16 years ago
A metal spacer probably doesn't apply to your application since you have an aluminum or steel window frame. Those materials alone cause thermal transfer which increases condensation, frost, etc.

Michael

Here is a link that might be useful: Non Metal Spacer
adriand123
16 years ago
It sounds like condensation in the wall cavity.

When you replaced the drywall 11 years ago, was there a vapour barrier behind the drywall ?

Is cold air infiltrating the wall cavity from somewhere, perhaps a neighbouring garage thats poorly insulated ?

The window itself may not be the culprit, although better ventilation in a bathroom is always helpful.

The fact that mould has grown right through the drywall implies the drywall is constantly damp, even when it not raining.

Rip out all the drywall around the window. Check for openings and gaps where air may be getting in. Spray foam the entire wall that contains the window.

Who knows whats in that mould, it might be toxic

Here is a link that might be useful: All-about-screen-doors

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