Damp in the corner of new house and black mould Damp can be a major issue in the home. Find answers to questions or post your own here.

[mrrossi]

Hi all

We've been decorating a house we moved into recently, it hadn't been lived in for a while and there was some damp/mould issues. The cause of issues downstairs was addressed and we assumed the small amount upstairs was just the fact the house had been empty.

However, I've painted the upstairs bedroom and noticed a week later black mould appear again in the corner. The wall feels damp. It's an exterior corner of the house, so I've been outside to check the condition of the wall - looks ok, and although there's a drainpipe running down that wall, it seems dry and watertight.

Any ideas please what the issue may be?? Could the plaster still have been damp from before & does it perhaps need treating/replacing?

Thanks
Ross

[stoneyboy]

Hi mrrossi,
I suspect your house has solid walls and if you look closely at the rendering on the opposite side of the wall where the damp is, you will see that the render has either been repaired or the outer render coat has fallen off.
You will have to get this external area checked, if you want to do this yourself throw some water at the wall, if it soaks in and does not run down the wall this may be your problem.
Regards S

[mrrossi]

Thanks, will check this!

[mrrossi]

Hi - couldn't find any obvious cracks on the wall outside, but treated with a product just in case. Think the moisture was still from inside - have now been using a dehumidifier all day long as it's collecting plenty.

Mould removed, walls dried - could see damp value of wall dropped - so applied anti mould paint. Also applied normal paint on top...

Next day, the paint has split - as per photo.

Is this because it was still too damp?? How do I dry out fully /re - paint??

[stoneyboy]

Hi mrrossi,
You probably need to allow the wall to dry out for a lot longer - this time of year possibly a month with dehumidifier running. Unfortunately the mould resistant paint is sealing in any remaining moisture in the wall, hence it is blowing off. You may have to strip off your new paint layers and repaint with acrylic emulsion which will, to some extent, allow the wall to breathe.
Regards S

[mrrossi]

Thank you - that makes sense. So: sand off. Paint again with normally "breathable" paint and keep as dry as possible, dehumidifer on etc etc and make sure it's not wet / mould doesn't re-grow and then once fully dry in a month or so repaint with the anti mould paint to protect in future?

[stoneyboy]

Hi mrrossi,
Damp issues in houses are the result if a number of different conditions. If you have used something on the outside which prevents rain ingress but allows moisture to escape and will be using something on the inside which also allows moisture to escape, then you should not need to use a mould resistant paint.
Minimising the mould problem is a matter of trial and error and a good starting point is what you propose.
Regards S