WTF happened to our wall?

November 1, 2020 12:37 PM

Sometime in the past few days, our previously smooth wall has developed some very weird texture issues. I'd like to know what caused it, so we can prevent further issues and properly repair it. Photos and details within.

The wall behind our couch was previously (generally) smooth, with the minor ding in the surface. However, I just noticed that there are a number of new textural irregularities in one specific area, approximately 5 feet wide and several feet high. Here is a link to some photos.

There are multiple types of texture issues:
- Bumps that look like nail pops
- Large patches of raised area, in irregular shapes and sizes
- Depressions/divots in a few areas
- New uneven areas in the paint, that look like dust/debris was caught in the paint while it was drying

I've looked back at photos of the area from a few months ago, and these things definitely were not there.

Potentially relevant factors:
- The wall has a ductless AC/heater on it, installed in July. We've used the AC without issue since then, and have recently used the heat a few times. The irregularities are not directly below the unit.
- There is a central air vent below the area, and we have had the furnace heat on a few times this month. But the furnace was used extensively last winter, and the couch position hasn't changed.
- We live in Seattle.
- The house is 80 years old, so there shouldn't be significant settling at this point (?)
- When they painted the interiors to sell the house (last year), it seems like they used shitty paint/didn't apply it properly. In humid areas of the house, the paint has developed these weird brown drips that seem like some component of the paint is seeping out (they're able to be wiped away, and appear on various surfaces, so don't seem to be a leak of some kind). We haven't seen this issue on the walls of the living room (the wall in question) but I wouldn't be surprised if it was some other kind of shoddy work (lots of half fixed things exist in this house)

As stated above the fold, I'd like to hear both explanations as to what occurred, as well as suggestions for repair. Thanks in advance!

posted by bluloo to Home & Garden (13 answers total)

Assuming that this is an exterior wall? My guess would be that when the ductless system was installed they did not properly weather seal any holes they put in the exterior wall and these are signs of water getting into the wall, making its way through the drywall where the nails have created channels of least resistance.
posted by topher74 at 12:57 PM on November 1, 2020 [2 favorites]

Response by poster: Topher, it is an exterior wall; however, the affected area actually does not face the exterior. There is a laundry room behind it, that may have been an addition at some point. So the area with the heater has exterior on the other side, while this portion of the wall does not.
posted by bluloo at 1:04 PM on November 1, 2020

these weird brown drips that seem like some component of the paint is seeping out (they're able to be wiped away, and appear on various surfaces, so don't seem to be a leak of some kind).

This could be tobacco tar that was not properly removed, or removed at all. It will eventually seep through paint.
posted by Splunge at 1:50 PM on November 1, 2020 [2 favorites]

Nearly every paint company has advisories online about those weird brown drips. Apparently they're evidence of a phenomenon called "surfactant leaching" that happens to latex paint in humidity. Wiping them off is the recommended treatment and they don't mean anything bad about the paint; apparently it'll last just as long and do its job properly despite the leaching surfactants. If the streaks were tobacco tar, they would likely be showing up in the living room, dining room, bedroom--you know, the places where people tend to hang out and smoke for hours on end. That it's happening in the particularly humid parts of the house indicates that it's probably just latex paint that cured in too-wet air.

I don't know what other than water could be causing the problem behind the couch. If it's not the AC, is it a roof leak?
posted by Don Pepino at 2:03 PM on November 1, 2020 [3 favorites]

weird brown drips that seem like some component of the paint is seeping out

That’s surfactant leeching out of the paint as it dries, it’s a common problem in some temperature/humidity environments. You pretty much just wipe it off with a mild cleaner and get on with life. That’s not related to what you’re seeing in the plaster, which looks like water damage. Try pushing one of those divots with your thumb, and I’ll bet it turns to mush easily.
posted by mhoye at 2:15 PM on November 1, 2020

I think the recent installation of the AC/heater is not a just a coincidence. I would guess they are related. It looks like water damage which you can verify by pushing a nail into one of those depressions and see if it is very soft.

The AC will create condensation water as it removes humidity from the air. This water has to drain somewhere and it may be improperly draining into your wall cavity.

And the brown drips are further confirmation of dampness. As others have pointed out, surfactant leeching doesn't generally happen except in the presence of moisture, for example poorly vented bathrooms.
posted by JackFlash at 2:41 PM on November 1, 2020

And another possibility. You say that the affected wall is opposite the laundry room. Are the water and drain fittings for the washer on that same wall. You could have a leak either in the water supply or a clogged washer drain pipe.
posted by JackFlash at 2:46 PM on November 1, 2020

Those raised bubble areas look very similar to what my wall looked like when the air conditioner started spilling water inside the wall. The paint & top layer of the sheetrock started lifting up.
posted by belladonna at 2:47 PM on November 1, 2020 [2 favorites]

Response by poster: JackFlash, the water and drain fittings are not on the same wall. For those in the water leak camp, I just tried putting a nail into a divot and a raised spot. Neither felt particularly mushy compared to the surrounding area, and took some effort to drive the nail in. The raised area did crack a bit around its edge, and that corner is now sunken compared to the surrounding wall.
posted by bluloo at 2:59 PM on November 1, 2020

If it is not the laundry, then I'm back to suspecting the AC condensate drain. Some are gravity drains and some require a small pump. Sometimes they just drain to the exterior and sometimes the drain goes through a hose to a plumbing drain pipe.

You may have to remove the housing of the AC to see what is going on. Should just be a few screws.
posted by JackFlash at 3:08 PM on November 1, 2020

Water was going to be my first guess, but if you rule that out - those pictures look like old, filled nail and screw holes where the filler is now reacting to something. Maybe the same temperature / humidity situation that is causing the brown spot issues with your paint is also causing the filler to contract or move? Never actually heard of it happening but those pictures sure look like poorly filled holes.
posted by stillnocturnal at 4:50 PM on November 1, 2020

Water. Not enough to make it *mushy*. Just enough to make the plasterboard or wood or whatever is behind there swell slightly, then redry like that permanently.

May as well sand it flat, because you'll be able to see if there is any current dampness happening behind there, and fiiix it, and otherwise you'd be doing that anyway
posted by Elysum at 5:12 AM on November 2, 2020 [1 favorite]

tangential: When I had weird brown drips on fresh paint, it was wallpaper paste coming through paint when the humidity was high.
posted by theora55 at 8:33 AM on November 2, 2020