bathroom difficulties...
December 11, 2013 10:29 PM   Subscribe

What is happening to our bathroom drywall?

The bathroom being a humid space, I'm thinking this may be mold (here and closer here. But I think of mold as being black or greenish, this is rust colored.
Can you identify what it is?
And can I clean it up without patching the drywall? (bleach & Kilz paint?)
posted by artdrectr to Home & Garden (4 answers total)
Are you sure it isn't rust? Could you have metal corner trim that's rusting because of the moisture?
posted by Emperor SnooKloze at 10:39 PM on December 11, 2013 [4 favorites]

Don't think so. I've poked around slightly with a penknife blade. Seems to be just paint & plaster put on the edge of sheetrock.
posted by artdrectr at 10:57 PM on December 11, 2013

"Don't think so. I've poked around slightly with a penknife blade. Seems to be just paint & plaster put on the edge of sheetrock." Corner bead is quite thin, think maybe between the thickness of expensive tin foil and a really cheap turkey pan.

Emperor SnooKloze has it. Remodeler for eight years here - that's rust.

On the less expensive and temporary side you can buy what is called "Rust converter". The downside being that it converts red rust into "bluish-black ferric tannate" which is stable but, well, bluish-black so you might have to apply a few coats of paint.

- Anywhere you see bubbling on the surface remove the material with a scraping device followed by a wire brush. Your goal is to expose the rust but, believe it or not you really don't have to get to the bare metal [if any is left].
- Apply the rust converter as directed.
- Paint

What your problem indicates to me is that the painters didn't use primer and there is an incomplete seal so humidity is infiltrating the joint compound and reaching the corner bead. Corner bead is perilously thin and yours will need replaced eventually.

I don't know if you rent or own but if you own it will be less expensive in the long term to just remove and replace the bead and have it redone properly. Have the drywall people remove and replace the corner bead and mud [with hot mud] and then sand, prime and paint yourself. Easily less than a hundred dollars.

Oh and btw - south Louisiana here - mold comes in a variety of colors.
posted by vapidave at 11:28 PM on December 11, 2013 [2 favorites]

You guys are exactly right. A little more searching and I found a metal foil there.

Vapidave: Thanks for your How To.
We upgraded this bathroom in our home 7 years ago, this is the first prob encountered.

Would you suggest I call the contractor and let him know this has happened?
After 7 years, I don't expect his company to do anything about it, it'd be just an fyi.
posted by artdrectr at 4:11 PM on December 12, 2013

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