Mold Under Primer

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Old 12-29-16, 12:21 PM
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Mold Under Primer

Well, this is embarrassing. House was built in 1986, drywall, primer and oil based paint. The room in question has only been painted one additional time, primed with Kilz or Bullseye, I believe, topped with latex paint. It is a foyer and I've kept the inner door closed a lot so it has gotten both very hot and very cold and high humidity. This may be the cause of paint starting to crack or check and flake in some areas, mostly just one corner, half on an outside wall, the other on an innerwall. An area under a corner shelving unit is the same, even though it still has only the original paint. As I scrapped, whole sections of paint came off down to the drywall, even some of the joint tape and in one place, and the paper covering on the drywall. In the area that is the worst, there is black mold at the surface of the drywall and/or paper joint tape. It is only surface deep.

So, my question is, what is the best way to repair and prevent it from happening again? In the section of corner tape that is loose on the ceiling side, can I slice off the top half and retape without stripping off the whole tape joint?
 
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Old 12-29-16, 01:09 PM
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If it was under all of that, I would be concerned what was on the other side of the drywall and be cutting an inspection hole.
 
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Old 12-29-16, 01:57 PM
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Thanks. Up in the top of the corner, where the two corner seams come together, I pulled out a piece of compound that was between the two wall panels. I barely scraped the surface and clean compound was revealed, clean all the way through. I don't see any mold in the wall where I can now see some of the blown in attic insulation. Anyplace where there is mold I can scrape a bit and it's gone. So you're saying that if there is any mold on the backside I have to tear out all the drywall?
 
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Old 12-29-16, 02:01 PM
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I would tear out the drywall and replace it with mold resistant drywall because now that you know this is a problem area and you may as well do everything you can to prevent it from happening again, because it might. The cause is likely a cold air draft... lack of insulation, seam in the sheathing or something like that, so when the drywall is off you can look for the cause of the draftiness. The cold wall (winter) probably sweats since the house is warm and that's where the mold is coming from.
 
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Old 12-29-16, 02:34 PM
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Thanks, XSleeper. Insulation shouldn't be the problem because we have 6" walls and probably 12" blown in the attic. Of course the attic has likely settled a lot. What is weird is that of the 3 outside walls, only one has the problem and it is close to the corner where it meets the inside wall. The worse of the bad area is an inside wall, all at the ceiling where it meets the wall. One cross seam is split for about a foot. If the mold went all the way through I'd suspect the roof. One half is just an extension of the house roof but the side with the problem is the half that slopes down, butted up to the siding. The roof is only a few years old though and the flaking isn't only there. There are minor spots scattered here and there, including along the floor in the corners, a place where moisture would collect. That is why I'm pretty sure it is caused by hot/cold and condensation. The same thing needs my attention in the downstairs entry, a room that is kept closed too much so it don't get much heat.
 
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Old 12-29-16, 02:34 PM
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The fact that the paint is peeling off down to the drywall concerns me. You could spend a lot of time scraping, mudding, sanding and still might have issues. I like the suggestion for replacing the drywall both from a painting standpoint and that it allows you to correct any voids in the insulation. Any drafts in the exterior sheathing can be caulked or spray foamed at that time.

While limited to white and light pastels, Zinnser's PermaWhite is a great mold/mildew resistant paint.
 
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Old 12-29-16, 03:37 PM
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Thanks for the paint suggestion. The problem with replacing the drywall is how to deal with the ceiling, which will dump all that insulation down on my head. Not a fun idea.
 
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Old 12-29-16, 03:55 PM
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One question please. If the mold is on the inside only, not through the drywall, caused by moist, cold air coming through the door, why are you suggesting it needs to be replaced? Mold loves drywall. When the paint cracked moisture crept in and that surface in contact with the moisture, molded. If I am going to do a major job I want to understand why. Thanks.
 
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Old 12-29-16, 04:46 PM
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It's called "remediation". When you have extensive areas of mold, covering more than just a few square feet, you remove the product with the mold on it to completely get rid of the mold. Minor areas of mold can be "encapsulated", but the risk of doing that is that the mold is still there, it's just covered up.

If you don't want to sweep insulation away in the attic in order to replace the ceiling drywall, you might be able to encapsulate the ceiling mold, and only remediate the walls.

In addition to using mold resistant drywall, you would want to use a mold resistant joint compound, such as Proform XP. Taking away the food that the mold enjoys is one of the steps you should want to take.

Mold needs 3 things to grow: moisture, a food source, and optimum temperatures. Remove any 1 and mold won't grow. My suggestion is to do everything you can. Tackle the reason the walls are cold (caulk sill plate to subfloor, caulk the joints between any stacked framing members like king and trimmers studs, ensure sheathing joints are sealed, ensure wall cavities are insulated, check partition corners for insulation (they are often hollow), etc. and then increase ventilation if possible, which will both warm and dry the walls. Take away the food source by using mold resistant products. Mold loves both joint compound and the paper surface of standard drywall.
 
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