I have just had part of my house replastered because of damp problems (penetrating due to rendered brickwork). Part of the lower kitchen wall was replastered with supposedly special damp proof plaster. The original plaster was spalling and the paint was bubbling. This was removed and the damp proof plaster applied (dark grey colour) then a skim put over the top of that.

As the replastered walls in the kitchen are drying there appears to be a white substance on the new plaster which I think is salt deposits. Is this normal? I thought damp proof plaster was supposed to stop the migration of these salts to the surface. Anyone a bit more clued up on these things? Will ring the builder later but I'd rather get a feel for what I'm talking about before I speak to him.

http://www.neverpaintagain.co.uk/article/Problems-with-plaster-walls-damp-repair

Did you find the cause of the damp initially?

Complicated. :) Ground level (concrete) to rear of property was level with the floor inside which would account for damp at floor level. I have created a channel in the outside concrete 4" wide by 8" deep to give recommended 6" or so difference in levels. Builder's injected a new horizontal DPC in the rear wall as well.

Entire rear elevation of building (including offshot kitchen) covered in pebbledash render which I'm led to believe would soak up rain and acount for the penetrating damp higher up (head height) in the dining room and hence the vertical waterproof membrane applied to that wall. I suppose the external pebbledash render probably needs painting with waterproof coating or one of those exterior paints as well. Same thing for the kitchen as the damp was from about floor level to 1.0m above and hence application of damp proof plaster.

I just thought that the damp proof plaster was supposed to stop the passage of water and also these salts as I believe it's this that damages wallpaper and finishes. Or are these salt deposits simply a one off from the plaster drying initially and I'm ok to brush it off and paint the plaster?

:huh: I'm no expert but I know that there needs to be some ventialtion or means of escape for moisture, otherwise it finds it's way out (usually where the damp proof ends)

IMO the white patches you see is the proof that the wall is drying out correctly and when it has all gone the same colour the wall is completly dry and is ready to be decorated.

Never wrong: The white patches I mean are salts on the surface of the new plaster which you can rub off with your finger, bit like a fine white mould. Think you mean when the plaster changes to a lighter colour as it's drying out.

I'm just puzzled, I thought the special damp proof plaster was supposed to stop the ingress of the water that carried these salts through from the brickwork, which in turn damages your wall paper or paint finishes. I'm leaning towards the opinion that they've just used normal plaster and hence why I've still got this problem. Will give the builders a call and see what they've got to say for themselves.

Redinsheff: Have got your PM message but computer says no. I can't respond until I've had 10 posts on this site.

I am a full time builder and depending on temperature, humidity levels and ventilation some walls can take up to 6 months to dry out in extreme circumstances. Sometimes you can get salt deposits on newly plastered walls.
Brush it off and see if it comes back. Do the walls or areas of salt deposits have kitchen cupboard units covering them? I'm wondering if the walls can breathe. I wouldn't paint anything until you have watersealed the render with something like thomsons waterseal and allowed time to see if the deposites return.

I am a full time builder and depending on temperature, humidity levels and ventilation some walls can take up to 6 months to dry out in extreme circumstances. Sometimes you can get salt deposits on newly plastered walls.
Brush it off and see if it comes back. Do the walls or areas of salt deposits have kitchen cupboard units covering them? I'm wondering if the walls can breathe. I wouldn't paint anything until you have watersealed the render with something like thomsons waterseal and allowed time to see if the deposites return.

Rang the builder and he pretty much said the same, keep brushing it off until salt stops appearing and don't paint for a few months. Good to know you can get this with newly plastered walls as well. Am a bit wiser and happier now. The Thompson's waterseal is a good idea. Thanks for your help on this olddirtydogg, much appreciated.

Oh...and the walls are not covered by units but the kitchen has always been a cold room so the if temperature affects it then I'll keep the heating on low in the kitchen for a while and keep an eye on it.

I wouldn't paint anything until you have watersealed the render with something like thomsons waterseal and allowed time to see if the deposites return.

Sorry - heard the word before - but what exactly is 'render'?

Is it inside or outside wall?

No worries Rockbaboon...as & when is fine!

Sorry - heard the word before - but what exactly is 'render'?

Is it inside or outside wall?


Render is like a cement skin on the outside of the house walls. Mine's covered in small stones and is like pebbledash. Looks a bit naff but nowt a lick of paint won't sort out.

Hi there - i have exactly the same issue as you - so i am curious what happened after you let the salts 'dry out'?

Hi,

I left the wall for months. Just kept rubbing the salts off the wall with a cloth...when it stopped appearing I just painted over it. No problems since.

Cheers