Weird drywall situation

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We had to do some repairs to some walls, putting up a few sheets of new drywall. We used Durabond setting type drywall compound, both all-purpose and then lightweight. We used Conco PVA primer/sealer and Pittsburg latex paint sprayed on with an airless painter. A few hours after painting we went back and found several spots where the setting type lightweight compound turned soft and bubbling up, but only over the old, smoke-covered walls, not over any of the fresh drywall. We also found a spot where no work had been done, but it is bubbling up too. We have more painting to do and don't want the same problems. Any ideas on what happened and how to prevent it? Thanks.
-- Mike D.
www.stopassaultnow.net
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You primed how long after the compound was applied? And was the primer fully dry before you painted with topcoat? Check instrutions on both the primer and the compound. I've had bubbling up from either not waiting long enough for first coat to dry, or by continued degassing of the plaster compound as it sets - I think it may be the latter. Thicker areas of compound can take a day or so to set up, depending on humidity, at which point it turns from dark and pliable to a sort of fully bleached , white look.
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The problem was in the thinner areas, not thicker, and setting time for the compound varied from one area to another, from about 1 - 2 hours. The compound has a 45 minute setting time. Also this only happened over the old drywall, not over the new. The new actually had the shortest setting time except for one thick area we missed earlier (holes and a dent), but that area is fine. It all sanded fine, fully set, before painting. Now the setting-type compound in certain areas are soft.
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Just because you can sand does not mean you can prime and paint. 24 hrs is normal , when area is humid, many days can be needed. water must evaporate. Redo it, this time wait
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The water does not evaporate as this is SETTING-type compound. It sets up in 45 minutes. Also, most areas are fine, even the areas that were done last.
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you didnt wash the walls first.
randy

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Setting time must not be confused with curing time.
Setting time allows for more than one coat in a day. Depending on room conditions and the thickness of the mud, final curing can take from 1-5 days. You can't sand or paint until after the final cure.
After final cure priming with a drywall sealer is desired. It dries much more quickly than regular latex paint. Once primed and dried you are ready to paint.
Colbyt
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Nothing was said on the package about that. How can you recoat if you can't sand until after the final cure? I can understand painting, but not sanding. I have done this many times before with no problems, but also never on old, smoke covered walls and never with that brand of primer.

We did that.

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Well you would be right about that. I went downstairs and looked at a bag. That is still the problem. If you go to the USG site it points out that the purpose of setting compound is to keep the production moving, allowing for extra coats of mud in a single day.
Most people don't sand between coats. You can shave any ridges and apply your next coat. Let the stuff dry and paint it again. Get some air moving in the room to speed the process.
Colbyt
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I keep my compound powder in a bucket so I didn't have the directions handy, but had to go to the HW store for something else and read the bag. It is paintable IMMEDATELY after drying/setting. That means it is paintable in about an hour, depending on how much water used, air and water temp (I accidently used hot water with one batch and it was setting up before I could even apply it), and humidity. This also does not explain why the compound softened, like it was still wet.

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You posted here with a problem.
I gave you the answer. If you don't want to accept that, I don't mind. I don't have a problem.
Have a great week.
Colbyt
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You gave an answer that contradicts the instructions and fails to explain how hardened setting-type compound would soften. We will not have an opportunity to paint again for a few days and we will see what happens then.

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"Mike Dobony" wrote

There's you problem, as already mentioned by _xrongor_. You don't prime/paint or use mud over dirty walls, you skipped the prep work, now you're paying for it.
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That might explain why it came loose, but not why the set compound became wet again. This is not cheap drying compound, but setting type. I have never seen setting type compound become soft again.
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It didn't become wet AGAIN, it just never dried. You seem to be confusing setting with drying.
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Did you use fiberglass mesh on the joints or that old paper tape? I used to use that paper tape and it would often peel off when it got wet from the paint. I no longer use that crap. I use the mesh now and dont have that problem anymore. You might apply a fast drying non-water based paint over the joints before you use your latex paint. Something like the alcohol based KILZ. Or, even try some spray paint, I never tried that, but it may work. The gray auto primer may work and will be an easy color to paint over.
Mark
On Sat, 5 Feb 2005 22:14:30 -0600, "Mike Dobony"

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Did you use fiberglass mesh on the joints or that old paper tape? I used to use that paper tape and it would often peel off when it got wet from the paint. I no longer use that crap. I use the mesh now and dont have that problem anymore. You might apply a fast drying non-water based paint over the joints before you use your latex paint. Something like the alcohol based KILZ. Or, even try some spray paint, I never tried that, but it may work. The gray auto primer may work and will be an easy color to paint over.
Mark
On Sat, 5 Feb 2005 22:14:30 -0600, "Mike Dobony"

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