Hi,

I plastered a shower room last Saturday. When I say plastered I mean skimmed, with a little bit of patching beforehand.

The radiator was removed and hasn’t been put back on since. And with the floor being concrete and the weather, it’s been chuffing cold in that room.

The outside wall is still drying out. The bottom foot or two is still dark and is drying out more each day.

I’ve plastered before and know what to do and can get decent results.

My question: on certain parts of the wall there is stuff on the plaster. Some of it looks a little bit like fur (which brushes straight off), and some feels a little bit harder than that. This is happening on bits of the wall which are still drying out in various places on the wall.

Is this just a reaction to the cold and damp atmosphere and can be ignored, or is there something more sinister happening? I can’t see any problems on the outside of the wall.

Many thanks!

Come on guys, all those reads and no posts?

Surely fur has appeared on someone's plaster before????

Cheers!

I have seen patches like this on new plaster, but I'm not certain what causes it. One possible cause is salts.

You'll have to wait for the pro's to reply

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DIY | Donnas dream house

thats hygroscopic salt being drawn through the plaster...
sound to me like its an external wall, solid construction and what you have is rising or penetrating damp..
failing that the origional substrate youve plastered onto was damp for another reason and as the wall is drying out its drawing the salts through into the room...
as long as youre sure you havent got an ongoing damp problem a 50/50 water and vinegar solution with a couple of drops of washing up liquid painted onto the wall after youve brushed the salts off will hold them at bay...
i'd let it dry properly first though...
you sound like you know what youre doing so ill not go into depth regarding damp bridging/membranes/insulation/penetration etc..

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http://www.peterborough-plasterer.co.uk/

Thanks for your replies.

I tasted it and it is salty (no jokes please!).

It is an external wall. It was chemically damp-proofed about three years ago.

The old wall was wallpapered, so I guess it could have been made damp that way, but what are the chances of the DPC failing? All I know about it is the holes they filled on the outside were with really crumbly render that I've had to patch up.

Should I get them back?

Thanks again.

Me again.

First off, could someone move this to the damp proofing section please? Many thanks.

I just phoned the people who did the DPC and explained the situation. They said it's more than likely an issue from old moisture in the wall (especially if it's only in small patches), and that i'd be advised to take it back to brick and treat it, and then re-plaster.

Now, that doesn't sound all too agreeable to me, having just plastered.

Could someone confirm that:
1) it's possible for a wall (in a small and condensation-prone shower room) to still have moisture in a wall where the DPC was done about three years ago?
2) Could it appear only when re-skimming (ie there was no salt before I skimmed)?

If so, at least I know I'm not being taken for a ride here.

I don't plan on being there too long, so a "suitable" remedy would be appreciated. I'm happy to do as cwplastering advises above. Can anyone second that?

A couple of other questions:
1) Is there a way to draw all the stuff out in one go?
2) If I paint over it, is the paint going to draw more out / get ruined? I'm planning on using Dulux shower room paint.
3) Would it be worth tiling a splashback along the wall over the areas instead of painting? Would this come back to bite me (tiles falling off, etc), or would it be alright?

Many thanks in advance!

FYI - There's no penetrating damp issue I can see.

sounds to me like a failed dpc... theres various ways to check it but the easy one is a damp meter reading at floor level moving upwards in 100mm intervals and if the readings diminish its a good indicator of rising damp...
either way, if they did the replastering they should have used washed plastering sand and a salt inhibiting additive in the mix for the render coat..
stops the salts coming through see?
the render shouldnt be in contact with the floor either, known as 'bridging' it gives the moisture a little bridge to permeate through so it gets round the dpc... hacking off the bottom 2" of plaster back to brick will solve this problem...
then just apply salt neutraliser (vinegar etc) and let it dry out as long as possible before it gets painted with a breathable paint...

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http://www.peterborough-plasterer.co.uk/

You are a very knowledgable person!

They only put in a dpc, they didn't touch the plastering. All sounds a bit slap dash to me.

The salt is only on small sections, so perhaps it could just be residue, and not a failed damp proof???

I'll do as you say, with the vinegar, and let it dry out as long as possible. I'll even whack a dehumifier in there, and put the radiator back on. And i'll make sure there's no plaster touching the floor.

As for breathable paint, that's where I come unstuck though. It's a very humid shower room. What do you suggest? Also, would tiling over it be better than paint, or should I be alright if I do everything as suggested?

Many thanks for your help!

should have re-rendered really, could well be residual...
try the old salt neutraliser and theres some paint you can get these days thats resistant to salts, alkali resitant i think.... best answered in the decorating forum mate..
as for the humidity what i would suggest is a 4" 'run on' fan wired to the light..
they take a permanant and a switched live, when you turn the light on the fan starts and 'runs on' for a preset time after switching the light off - 5 minutes or so...
only one way to get rid of condensation, literally get rid of it by means of increased ventilation...

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http://www.peterborough-plasterer.co.uk/

Cheers fella.

Did you watch them install the chemical damp proof course?
Did they knock the plaster off to a height of about four feet and then use a waterproof render?

Damp rises through a wall via the air holes entrained in the mortar when it was mixed and as you probably know it rises to about four feet above the outside ground surface, higher if it is enclosed.

Most often the person drilling the holes does them either in the second row of bricks or in the junctions of the mortar at the bottom of that row.

This means that the bottom row of bricks is still wet and to finish they use a waterproof render to hopefully? Stop the damp rising?

If they did it that way, you can improve on the job by going round again at floor level and drilling down at an angle through the mortar to lower the damp proof level and take it down below the floor
.
Have you checked the height of the ground outside?

Is there anything bridging the new dpc?

A dpc works best when the ground outside is more than 9 inches below the dpc. Any higher and the rain will hit the ground and bounce up above the dpc making the wall wet.

And as mentioned earlier, poorly mixed mortar can result in wind blow rain blowing through the wall and making the inside wall wet. Do you have an exposed wall?