Someone put joint compound over the poured concrete basement wall and then painted over it. This seepage isn't water--it's a little sticky where it hasn't dried, and it appears in a few other spots in the basement.
I want to just paint over this but I was going to use a nicer latex and I'm concerned it'll bubble... but I don't even know how this paint hasn't been ruined. Any ideas on what it is, and how to not have a latex paint get ruined by it?
This seepage isn't water
I'd be surprised if it's not. Seriously, that's probably some level of water getting into the plaster. Concrete is porous and can let some level of water in. Even if it's not seeping in from the outside, the wall is in a cool, damp place where it can condense moisture in the air.
Someone put joint compound over the poured concrete basement wall and then painted over it.
To call this sloppy would be an insult to every DIY hack out there. This was plain negligence. Have you ever asked yourself "Why doesn't this happen to walls normally?". The answer is simple: vapor barriers. This is why you put faced insulation in walls. This is why you don't just bolt drywall to concrete (or be even lazier and just slap drywall mud on it and call it good).
The way to fix this is you need to air gap the wall. The normal procedure here is you frame the concrete wall with 2x4s like a normal wall (using pressure treated wood for the bottom plate that will be sitting on concrete), then add faced insulation, and finally drywall.
It's also a good idea to make sure nothing can seep in from outside. There's supposed to be a whole ecosystem of things your builder did to ensure water moves away from your foundation. The good news is the water seems to be seeping in from the top, not the bottom. That could just mean you have a minor drainage problem. Check to make sure no water can pond near your foundation, and that gutters can channel the water away.
You haven't told us what the age of the house is or where you are located but here's the thing: if you have an old house and you are getting water through your walls, it's likely related to your (now defunct) drainage.
Back in the middle of the 20th century, a lot of homes were built in the US. At the time, they used porous ceramic drainage pipes. This is why people call plastic drainage pipes 'drain tile' to this day. I remember as a child digging in my (parent's) yard and finding these bits of ceramic. They were crushed 'drain-tile' pieces.
The standard design of such systems was to lay this porous 'drain-tile' around the foundation or a home. The idea was that if any water drained towards the foundation, it would seep into the system and be routed away. This was probably a fairly effective approach as long as the system drained to somewhere.
Here's where the problem comes in. Those bits of ceramic I was finding in the soil were from the drain tile but not the part next to the foundation. What I was finding was the remnants of the part of the system that was supposed to take the water away. The ground shifts. Tree roots crush clay pipes like twigs under a truck tire. What these homes are left with is a porous pipe wrapped around the foundation with nowhere to drain to or at least it doesn't drain well. And to top it off, a lot of these homes have downspouts that run into this weeping pipe up against the foundation.
The water has to go somewhere and that somewhere is your foundation. A lot of people will see water coming in and think, "I need to waterproof my basement from the inside." I personally think this is a dumb idea. The goop that is coming in is likely a mix of water from the outside and whatever chemicals have been applied to the walls.
What's the answer if you are in this situation? Call a landscape company that does drainage. They will reroute the water away from the foundation. It probably won't be cheap so get a few estimates and make sure they are legit. You might even want to dig up the clay tile around the foundation and get rid of it.
Someone put joint compound over the poured concrete basement wall and then painted over it.
How long ago?
They skim-coated a concrete wall with joint compound?
This seepage isn't water--it's a little sticky where it hasn't dried, and it appears in a few other spots in the basement.
Joint compound uses glue as a binder. The seepage is likely a water/glue mixture.
If you're looking to just paint it and forget it then you'll need to use an oil or shellac-based primer to hide the stains first. Then you can use a nice latex color paint. If you don't prime then the stain will seep through the latex in a matter of hours. Regardless, assuming you don't fix the water infiltration issue then the stain will re-appear at some point.
