Any Sherlock's out there?

[jungle_jim01]

Ok here's one that's baffling me, so going i'm to put this out there in the hope that someone's detective skills might solve the problem...

We finished painting a room a few weeks ago in breathable clay paint. We've had damp problems in other parts of the room but mostly sorted i hope. However there's an area of paint a few inches across that has bubbled. It's on an internal brick wall and about 3ft above the floor and about 2ft from any other wall junction...very random! It doesn't feel damp to touch but i presume that it must be slightly for the paint to bubble. The thing is i can't work out how/why it's damp.

Over to you?

 

[Penners]

I don't know much about clay paint, but I suspect that a number of factors might cause it to bubble - just like modern paints. So the cause might perhaps be some impurity on the substrate, rather than damp. Could it ever have been painted with some kind of sealant, or some such, that could have reduced the adhesion of the paint?

 

[jungle_jim01]

Wow that was a quick reply! We painted onto fresh plaster with a diluted mix as instructed on the tin. The rest of the wall is fine, apart from this area a few inches across, so i'm assuming that the paint has gone on ok.

 

[MdB]

We painted onto fresh plaster

Gypsum or Lime?

If gypsum is overpolished it produces a layer that is very difficult to get paint to stick to and is often only in a small area. (I did this )

I don't know if lime does the same thing.

 

[jungle_jim01]

Yeah gypsum plaster so could be something like that...did you manage to solve it? maybe with some kind of primer?
I seem to remember that the area (or certainly close to it) didn't dry to to the lightness that the rest of the wall did. It was dry to touch though and being in the middle of a wall i presumed that it was a dry stain and not damp.

 

[MdB]

I was thinking of sanding the spot lightly to give it a key - which probably would have been the best thing to do - but in the end just put a few more layers over the top. I was only putting on trade emulsion (basically lime wash) so bubbling was never going to be an issue - it was more just getting it to cover properly.