What to do with this wall

[Mickmeister]

There was a dark spot on the bathroom wall in a corner by the shower, so I decided to scrape it down and repaint. But it turned out that the paper covering on the drywall was slightly damp and scraped off very easily - so I ended up scraping the 10" tall area shown in the pic. So now the plan is to prime with a stain blocker paint, fill in with drywall compound, prime again, then paint. But the problem is, I did the scrape job about two weeks ago and the area still feels cool to the touch - so I'm wondering if it's still slightly damp. Could the moisture be coming from some problem behind the wall, or is it just absorbing moisture from the air (it's been humid as hell here for the past few weeks). I'd hate to do the repair job, then later have it ruined by moisture.

[pushkins]

Without any doubt that area is absorbing moisture from a small leak in the shower area, that is an extremely common area to see type of problem.
Is a tiled floor shower or is it a fiberglass pan with tiled walls ?

It looks from your picture to be a tiled floor and wall type, so check the caulking on the shower door to wall, make sure your not getting water splashing out from a glass door that doesn't close correctly and most importantly check the caulking at the very bottom of the door frame where it meets the door frame bottom guide.

[Mickmeister]

You're correct - the shower stall is all tile, no fiberglass. Here's a wider shot. As you can see, the bad spot is to the right of the shower stall. But the shower stall seems to be watertight...after a shower there's no water in that area. That's why it seems weird that there was moisture damage in that area...I still can't figure out where it came from. It was never dripping wet there...just the damp paper that I scraped off, and now a slight dampness in the darker part of the scraped area.

[pushkins]

Like I said previously check the grout and caulking on the inside bottom right corner, that water stain is radiating out from that corner. The moisture can come from a crack in the grout a little higher and run down as well, but my money is on that bottom corner.

Post a picture of the right inside bottom corner showing the bottom and about 12" up please.

[Mickmeister]

Here's the inside view. I know, I need to make friends with some Spic n' Span, don't judge...

[pushkins]

Clean that bottom corner of any mold or loose caulk and reapply a new bead of 100% silicon caulk. Make sure you let the area dry well before applying new silicon. You also might want to do that whole corner area down across the curb and down onto the shower floor corner.

[Mickmeister]

Hmmm...I'm still wondering how the water could get from inside the shower to the damp area on the wall. I would think it would have to cross over the narrow strip of the tiled shower stall wall seen in this pic...I've never seen this area wet. I just tried running some water and everything outside of the shower stall is bone dry (except the damp area of the wall which has remained damp since I scraped it three weeks ago). The other thing I just noticed now is that hole to the left of the window sill. Do you think it's possible that water gets in thru there when it rains, then drips down to the problem area (which is directly below - not seen in this pic)? I'm also still wondering if the water could be coming from a problem behind the wall (hopefully I'm wrong!)

[pushkins]

Is the shower head on the same wall as the water damage ?
Yes it is possible that the window is leaking and water is running down the king or jack studs that are located exactly in that area, so that's a possibility.

Behind the tile there should be cement backer board but at some point on the wall it has to transition to drywall, IF there is a leak in the grout then moisture gets back to the backer board (which by the way gets moisture on it in normal shower use) when drywall touches the damp backer board OR gets wet directly from a small leak that is exactly the damage your seeing. The edge tile will most likely be partly glued to the backer board and partly glued to the drywall as it transitions to the painted wall area.

Typically larger leaks like from a pipe show major moisture issues and the damaged area rapidly gets larger, usually (not always) the same for window leaks, the drywall starts to stain all the way down from the leak, your damaged is very localized.

[Mickmeister]

It's starting to make sense now...if water were leaking through a crack in the grout then travelling behind the wall over to the problem area, it would explain why I never see water between the shower stall and the problem spot. So that's the leading theory right now. The shower head is not on that wall but on the adjoining wall to the left, and when it's running it's blasting water right into that lower right corner of the stall. And there does seem to be a crack in the grout in that area (you can't really notice it in the pic, though). So I guess the plan now would be to caulk up that crack, wait to see if the bad spot dries out, then proceed to fix up the bad spot as outlined in my first post.

[pushkins]

Technically it's not traveling "behind" the wall, it is traveling between the backer board and tile, the drywall acts like a sponge and once it starts drawing the moisture towards it starts to siphon moisture towards it.

Glad you have it worked out.

[Mickmeister]

Now I just need to find the time! Thanks a lot for the help, Pushkins.