Strange paint drying issue...

[Michael Forde]

Hey folks! I have an old covered chimney. When I moved in the paint over it was flaking. So I stripped and repainted. Primed it first. However the paint has dried strangely. Partly darker around the same areas there was flaking before. Any ideas how to solve this? Or of there are any underlying issues?

 

[sparkwright]

Looks like a cold or damp spot to me.

They say blocked up chimney breasts should have an air vent fitted.

This dark patch is where the fireplace opening would have been.

 

[opps]

If the chimney is still vented, AFAIK, there should be an air vent.

That said, old water stains will discolour emulsion. What did you prime it with? What is the substrate? Plasterboard.