sealing interior painted wall before repainting

[reg091]

I am trying to sell a flat which has now been empty for many months. Damp patches have appeared on some of the walls that were never there when I lived there. They are generally in the middle of walls with no damp above or below.


I had a surveyor round to look and he advised that it was not penetrating from the outside, or rising. (We took an electrical socket off in the middle of one of the patches and the plaster behind is bone dry). One of the patches is at the base of a wall but the skirting there is bone dry, suggesting not rising damp. None of the patches show salts.

His diagnosis is that it is moisture from within the flat being drawn into the walls from the inside, where those walls are likely to have a very cold exterior to them (old house, no cavity). This is due to no heat being on and no movement of air in the flat as it is unoccupied.

His advice is to dry out the flat/walls, mould kill them with bleach, seal with diluted PVA and then paint with silk rather than matt. All sounds sensible to me (and a cheaper option than I was imagining if it was rising damp etc).

However, I am a bit concerned over the PVA advice as I read everywhere that it should never be used if you are going to paint over it. He is an experienced surveyor so I trust his advice but what is the opinion here?

 

[kbdiy]

Paint does not stick to PVA - ignore his advice.

 

[Bosswhite]

Depends if you are prepared to take an experienced surveyors advice (who has probably never painted a wall in his life)
or an experienced Decorators advice who paints walls every day.

 

[dcdec]

"Seal" is a strange choice of words from a professional. It may well need stain blocking and this may be what he meant. As said PVA is not the way to do it. Agree with the bleach solution, dilute three parts water to one part bleach and wash off with clean cold water. Apply one of the zinsser stain blocks once dry and prior to painting, or thinly diluted OB undercoat as some prefer (apply with a mini roller).

 

[joe-90]

I've used dilute PVA in the past with no problem. It's just when it gets shiny that you have a problem.
He is right about the cause too. It's called 'interstitial condensation'.

Play safe and use a stain block and you should be OK.

 

[reg091]

Thanks for the info folks.

He may not have used the word "seal" but I interpreted his words to mean that. I guess what we are doing here is preventing the moisture from the room getting drawn into the wall. I would think that the silk paint will do that anyway (moisture will run off it rather than be absorbed), but I guess adding another "barrier" behind the top coat is sensible.

I will return the PVA to wickes and get a stain blocker instead.