Replacing moldy bathroom ceiling....need advice

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Old 01-04-11, 09:18 AM
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Replacing moldy bathroom ceiling....need advice

We are remodeling our bathroom and want to replace the old drywall ceiling with new drywall. We don't want to pull the old one down because we have over a foot of blown-in insulation in the attic but we are concerned about covering up the mildew on the old drywall. If we treat it with a mold killing solution, will it be ok to install new drywall over the old drywall? Thank you for any advice you can give us!
 
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Old 01-04-11, 10:53 AM
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Bleach and water is effective for killing mold and mildew and you should be able to put up new drywall once that's dry

Bigger question, in my mind, is why was there mildew in the first place?

By the way, welcome to the forums
 
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Old 01-04-11, 10:55 AM
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Mold generally needs 3 things to grow. A food source, the right temperature, and the right humidity. Take away any one of those 3 things and mold will not grow.

Using that logic, a person "could" drywall right over a concentration of mold (encapsulating it) and if that surface is cut off from moisture (steamy air), it would be fine. On the other hand, drywall is not a vapor barrier, and a 2nd layer of drywall will not completely stop moisture from migrating upward. So you cannot guarantee that you won't have a recurrence of mold growth between the layers.

Best advice I could give is to just get up in the attic with a scoop shovel and scoop the cellulose aside to expose the bathroom ceiling. Remove the affected drywall, reinstall the new, then scoop the cellulose back where it used to be.

If you want to take your chances, that is up to you. It will probably be fine for a few years until the same thing happens again. You might get a longer life if you use a paint with a fungicide.

Bleach kills mold, but does not guarantee that mold will not re-grow, given the same conditions. Mold is present in every bit of air we breathe, so it will be back unless the conditions change somehow.
 
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Old 01-04-11, 02:04 PM
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It is highly likely that the insulation above the bathroom is mold infested, too. It is highly UNlikely that any action short of removal of the ceiling and the insulation followed by thorough disinfection will prevent a reinfestation in the near future.

Bleach is effective for killing mold on the surface, but nearly worthless for what has gotten deep into the ceiling joists because the chlorine dissipates too rapidly. You would have to saturate the insulation to disinfect it which destroys it's R-value. I have had good results in the past with a product called Mil-Go, but I don't have a current source to recommend. It is a water-borne product which still doesn't help with the insulation.

The bottom line is that a shortcut fix will result only in short term relief. I know what I would do.

TLDoug
Builder/Remodeler
 
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Old 01-04-11, 03:12 PM
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Does the bath rm have an exhaust fan? installing one [or maybe a better one] should be part of the remodel plan. Is there any reason other than the mildew that makes you want new drywall on the ceiling? Generally drywall can be repaired easier/cheaper than it can be replaced.
 
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