New plaster not drying out

cherydee

We have had trouble with damp/condensation on one of our outer bathroom walls for years. Recently we fitted an extractor fan on this wall and also had all the walls and ceilings re plastered. The wall that was particularly bad had new plaster put on over two days as it was quite thick. This was done 12 weeks ago and all the walls and ceilings (bathroom is two rooms with arch through) dried within a couple of weeks. However the wall where it was applied thickly still has patches of dark pink and these patches were the places I had trouble with damp/condensation before the new plaster was applied. When I have a dehumidifier running all day the patches almost disappear completely, but as soon as its switched off it slowly returns to the dark pink. We have now painted with a thinned down emulsion on all the walls apart from this wall, so it's holding us up from getting the room decorated. Can it still be drying out after all these weeks, pleased it wasn't the winter when we replastered. Any help would be appreciated.

Southend1

Sounds like the damp is penetrating from outside. Have you checked the roof, gutters etc and that there are no damaged bricks or mortar on the outside wall?

cherydee

That had crossed our mind, but it's an old Victorian house that was rendered (sort of a painted pebble dashing) before we moved in and we've been here 28 years.

cherydee

Roofers were up just before the plastering was done to open up the sealed chimney to help with ventilation and when they opened it up it was divided into 6 so 6 metal vents are on the chimney top now. The wall we are having trouble drying out though is not the chimney breast wall.
As we cannot see if water is penetrating through the rendering is there any kind of clear waterproof coating we could put on the outside wall ?

Norman_Castle

If the damp is above ground level its unlikely to be from outside as there has been very little rain recently. I had a serious roof leak which saturated the brickwork. After re plastering and extremely slow drying I used a room fan directed at the wet plaster which worked really well. As you describe, a dry area would be wet again the next day. This is due to the surface drying then moisture seeping through from the brickwork.
The current wet weather may be a good indicator of if water coming from outside..

cherydee

Thanks Norman, bathroom is above kitchen so not on ground level, my husband seems to think what you say is more likely as when they opened up the chimney the brickwork was soaking. Today has been the only really wet day we have had in ages. Just going to have to wait and see. Maybe paint the other walls and finish this one off when sure it's dry.