I'm sorry for asking a question like this on here...but i know there are some great experts on all things building and construction.
Have a downstairs toilet which is a brick lean to which leads from the bathroom (part of the main house). There is a good extraction fan which is now running (Although was broken for a few months, my son didn't tell me). We've owned the house 5 years. Careless children tend to shower with the door to the bathroom open - the walls of the toilet are often very wet with condensation after someone takes a warm shower during winter.
The toilet has always been abit damp - its a single skin brick build lean to which was originally the outdoor bog. But with a coat of eggshell, very occasionally in the winter we give the walls a bleachy wipe down and never had any more issues. We never really had any problems in the bathroom either although my moisture meter always shows walls are a bit damp in the winter, but in summer they dry out. We've never had paint peel or mold form. An ambient moisture detector in the bathroom/toilet shows moisture is at 83% at 18 degrees this evening - the walls throughout the bathroom/toilet show moisture using a pin moisture meter (in masonry mode) at about 19-20% versus 15-18% in the rest of the house. The single skin toilet wall shows a reading of about 24% but the paint never comes off the wall...and It's an ancient single skin lean to.
View attachment 147246
In February last year I noticed under the bathroom rail that the towels sit on that the emulsion paint was bubbling (adjacent to the toilet!) so decided to scrape it off, give it a coat of zinsser and then a coat of eggshell. I assumed wet towels had just made things quite humid under there, and that a coat of paint would fix it. I was pleased with my work...
View attachment 147251View attachment 147252 ...but this paint has almost immediately bubbled.
And alarmingly the wall that joins the bathroom to the toilet has now started going completely furry with salty damp patches of soft plaster which are a little yellowy/brown. The damp meter but the reads at 26-27% on this wall all the way upto about 6 feet where the reading goes back to 22-24% of the rest of the bathroom. This doesn't seem to be a drastic difference to be, but i know these pin moisture meters aren't that reliable.
View attachment 147247View attachment 147250
I've been next door to check what is going on the adjoining wall – which is also a bathroom, but they have no issues or obvious leaks, I checked under their bath, everything was dry.
What i cant' work out is why this wall (which makes up the doorway) seems to much damper than everywhere else in the bathroom. It is an internal piece of wall, there is no water supply, the damp appears to be coming from the ground. Is it caused by this being where the warm air from the bathroom meets the cold air of the toilet? It seems unlikely considering that this problem also seems to be occuring on the bathroom side of it. Could a damp course have failed on an internal wall like this? I suspect not having the heating on now for probably a year hasn't helped... the rest of the house gets blasted by the log burner when it's cold.
Can anyone suggest what I should be doing here? Thanks so much, Joe.