Drywall – What plaster compounds should be used when plastering an unheated building

A few additions to Jeff's advice if you decide to replace the damaged drywall.

1. I'd suggest you look into waterproof drywall or mold resistant drywall. There are various products that do a better job than the typical green board that you would use in the bathroom that will help if you are installing in an area that has a lot of exposure to the elements.

2. Double check the thickness of your drywall if you are patching. If you replace a 5/8" with 1/2", you'll notice it.

3. Use screws, especially on the ceiling. They take more time, but hold better and are less likely to cause the nail pops that you are seeing.

That being said, I think it's entirely possible that you're just more aware of drywall issues and there may not be anything wrong. To know for sure, I'd go up to the attic, pull up the insulation where you suspect damage, and look for water rings or other mold growth. Use a flashlight, no need to feel with your hands (and risk falling through). While you're there, check the insulation for blackening that would indicate mold is growing there, and if so, replace any damaged pieces.

Your ability to see the joints between the drywall is just a sign of not enough paint and/or primer. And popped nail heads are normal as a home moves. My personal plan is to replace all the popped nails with screws and double up on the spacing the next time I paint to minimize this issue.

Andrew, excellent question and great photos. The problem is a bit complicated. I can see from the photos that the water migration is coming from the top, perhaps even above the top of your window. Anytime the plaster separates from a concrete base, it means the moisture is coming through the concrete, most likely from the out of doors in your case. Unfortunately the proper fix would have to be diagnosed and repaired outside at the source of the leak. Since you have no assess to the outside to explore and repair, the only mitigation to the problem from the inside would be to seal the concrete with a hydo-seal product such a Dri-loc sealer. I really think trying to replace the scratch and finish plaster coats will be a waste of time and fail again soon. I would strip away all the plaster to bare concrete in the effected area, making a clean line at the end of the bad plaster. Attempt to dry it as much as possible with a fan or fan forced heater. Something like a small box ceramic heater would be fine. Strip out as much of the caulking from around the window frame as possible. Paint the concrete with two coats of the Dri-loc sealer. Let it cure completely, recaulk the window frame with a Silicon/Acrylic paintable caulk. Paint the sealed surface with a recommended type of paint compatible with the sealer you select. You will not have as nice and smooth a surface as the original plaster, however, since you cannot stop the source of the water, the goal here is to simply stop it from entering your window bay.