# Mildew on Drywall Joints



## Bryan Holland (Oct 30, 2009)

We had a homeowner request us look at a drywall issue he is having with a concern that he may have a serious problem.  The location of the problem is on the ceiling of his lanai.

Upon inspection, the taped joints and seams along the lengths and edges of the drywall are mildewing.  The drywall is textured and painted.  The lania has screened openings and a common roof with the main portion of the dwelling, so open to mositure / humidity is always present.

What is going on?  Why is mildew only occuring along the tape seams and not any other surface of the drywall.  Any comments are appreciated.


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## JBI (Oct 30, 2009)

Re: Mildew on Drywall Joints

Bryan - Not sure, but if I were to hazard a guess, the moisture may be travelling in behind the joint compound between the panels (usually a small channel where compound doesn't fully fill the gap?)


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## globe trekker (Oct 30, 2009)

Re: Mildew on Drywall Joints

Bryan,

In conjunction with what John has suggested, possibly the seams cannot get air

flow across them sufficiently enough to regularly dry them out.

Your homeowners may want to consider another type of ceiling...


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## brudgers (Oct 30, 2009)

Re: Mildew on Drywall Joints

The gypsum board is probably fiberglass faced to inhibit mold.

The tape is probably paper and provides a suitable substrate for mold growth.

Gypsum board is often not a suitable for exterior celings.

It looses it's integrity over time due to moisture and ceases to provide lateral stability to roof trusses.


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## mtlogcabin (Oct 30, 2009)

Re: Mildew on Drywall Joints

Ditto brudgers comments just wanted to add the borax in type X will have a better resistance to mold than regular drywall


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## peach (Oct 31, 2009)

Re: Mildew on Drywall Joints

Gypsum board is *never* a good option for exterior applications (especially in a humid climate - it absorbs and holds moisture); around here, we see alot of bead board ceilings (also, not a good choice - but better than gyp)...   better off to use sealed T&G for a finished look, or just brace the trusses and leave it open.


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