Is the wall with the mold an exterior wall?

Sammy, there's mold on all four walls, about the same amount. One of the walls used to be an exterior wall, but probably before this wallpaper was up (judging by the paint layers).

other stats: we're in WI (humid summer and dry winter), full bath is above this, never seen evidence of any leaks in this area, mold doesn't appear worse in one area or wall.

It looks like drywall...if it is (and not plaster), it might actually be easier to remove it and put in new.

What I see for mold on the walls, can be removed, but, I would worry a bit more about what is behind that drywall. There could possibly be a leak from that upstairs bathroom, or maybe was at one time. I agree with Fori, if its drywall, remove it and start new, just so you can see whats going on in behind it and avoid future problems. It wont be a lot more work, than you are already going to have cleaning all that up.

It is drywall, not plaster.

It seems to me it molded because they used a vinyl paper over a glossy smooth finish and trapped moisture. If it was applied during a rainy spell in spring, summer, fall, then even more chance to mold. The mold spots are slightly more concentrated toward the ceiling but they are really distributed everywhere under the paper. We gutted the upstairs bathroom several years ago, I am confident it's not a leak issue.

We unearthed a heating vent they tiled over in 1980, happy to have that back.

Any thoughts on what the sticky aqua blue stuff is?

We unearthed a heating vent they tiled over in 1980, happy to have that back.

Any chance that was in this bathroom?

If you’re keeping the base and trim, I would wipe it down with bleach water, dry thoroughly and skim coat it.

Yes, the blocked vent is in this bathroom. WHY WOULD ANYONE IN WISCONSIN TILE A BATHROOM AND COVER THE HEAT SOURCE? Good grief.

I washed part of a wall and got the paste off easily with vinegar and tea tree oil, the mold appears about 50% lighter. With no trim, floor or fixtures, it seems a good time to just tear out the drywall. At least I can raise the light fixture to an appropriate height and get rid of the recessed t.p. holder too. Maybe add sound insulation. So much for a mini reno.

Vinyl wallcovering + no ventilation = mold

I’m going to mark this case CLOSED.

Right on, Sammy. It's just not right to cover up something shoddy.

I'd still like to figure out what this weird tacky aqua strip is...so curious...someone will tell us someday.

Thanks to all for chiming in.

Could the aqua strip be paint that may have been under a border at one time? Just guessing here. No real idea. I would worry though, that the mold may be on the backside of the wall too.

It's definitely not paint. I'll get more photos when we demo. It will feel good to know it's all done right and mold free. I'll get tea tree oil all over those wall cavities!

How can you stand the smell of that stuff. I just threw out a whole bottle

It's refreshing! And such a great chemical-free antibiotic and fungicide. It's great on mold and infections (people and livestock). Lice don't like it one bit either. The pure oil is really intense but it dissipates pretty quickly. I put some in a 2 oz spray bottle and mist it in our mudroom and bathrooms sometimes...it keeps the cat from investigating teenager's stinky shoes...

I wonder if someone tried to decoupage paper or tissue paper to the wall? I remember that being a thing in the early 2000’s. 🤷‍♀️

Good that you are doing the right thing and removing the drywall.

When we remodeled our kitchen we found some old water and termite damage. I told my GC to keep tearing it all out until he got to clean undamaged wood ... like a dermatologist removing cancer! He was happy I wanted it all removed and he said that many times clients will tell him to just cover damaged stuff up and not fix it correctly.