Best paint for external wall with possible mould / damp

[markymark1234567]

I have a brick out house just outside my house and I have now added a door on one side and bricked up the other Side so it is actually attached to the house now.
My problem is the walls which were exterior are now interior and these have started to make the old paint flake off and like a white flaky is stuff is growing around it.
I've brushed it off with a wire brush but I want to treat it, can anyone recommend any product?
Cheers in advance

 

[timbook]

Owatrol and Zinsser do good damp proof/anti damp/anti mould type paints which should be useful. Again, I think even a basic dehumidifier will protect this new 'extension' from getting any mould.