Fresh Plaster Showing Damp?, Chimney Breast with Photos!

Reginalddean · 13 Nov 2008

Hi, Latest Saga!

I had my chimney breast replastered about 4 weeks ago, it was taken back to the bricks before being replastered.

I have noticed I could see the outline of the bricks as its been drying, however, when its wet outside the outline seems to become more obvious, it is almost as if it is more visible and actually damp along the mortar lines?

Is this normal, should I be worried? My initial thought is its condensation but not sure?

I have inspected the inside of the chimney breast and there doesn't seem to be any moisture coming in from the outside and Im guessing if it was trickling down the chimney the upstairs one would be damp too?

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Reginalddean
13 Nov 2008
1

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Reginalddean
13 Nov 2008
1

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Reginalddean
13 Nov 2008
1

noseall · 13 Nov 2008

hygroscopic salts.

stuart45 · 13 Nov 2008

It could be a problem known as grinning. If the plaster is too thin, the joints can show through. This because the joints will absorb moisture at a different rate to the bricks. The salts mentioned in the previous post will attract the condensation.

Reginalddean · 14 Nov 2008

Many thanks for the reply,

Is there a way to cure this, if I have a few real fires will it fry the joints out, can I then paint over it to seal the joints in further?

Im not sure the thickness of plaster is the cause as the plasterer built the new coat up to the coving so it should be as thick as the original plaster?

Cheers

roughcaster · 14 Nov 2008

Just a pity that when you took the wall back to bare brickwork, you didn't scratch coat it first with mortar/waterproofer admix , and then plaster. That would have stopped the salts etc coming through the gypsum plaster, which are notorious for this type of problem

Roughcaster.

Reginalddean · 14 Nov 2008

Is there anyting I can do to solve this?

My current thought is to paint over the plaster with 50/50 water emulsion mix and then paint over that in a few weeks with the final colour

Is this a bad plan?

stuart45 · 14 Nov 2008

The problem with hygroscopic salts is that they will attract moisture in to the wall, even when the R/H is quite low. You will probably find that the wall is always damp and the decorations get damaged. These salts are often found in flues because of the burning of fossil fuels.
Its probably better to sort out the problem now before you install your fire and decorate.

Reginalddean · 14 Nov 2008

Thanks Stuart

Can I ask, how should I sort out the problem now? When the old plaster was on there didnt seem to be a problem, not sure why it has uddenly become a problem?

Cheers

stuart45 · 14 Nov 2008

The old plaster may have had a sand/cement render under the plaster.
This can help stop the salts. The new plaster has also wetted the brickwork which helps the salts move in to the plaster.
Was the old plaster defective?
Normally when nitrates and chlorides are in the wall the remedy is to hack off and re-render. But as you have only just had it plastered you probably don't want to do this. There may be a sealer that can help hold them back.

noseall · 14 Nov 2008

use an s.b.r. and cement slurry mix and paint it onto the masonry.

whilst still tacky, render the wall with a plaster sand and cement mix with s.b.r. added to it. you can add waterproofer to the plaster too.

Reginalddean · 15 Nov 2008

Oh dear, doesnt sound good!

Is this something the plasterer should have know and addressed before replastering the wall? I can guess his response if I ask him to come and rip it all off and redo it!

Cheers

noseall · 15 Nov 2008

Reginalddean said:
Is this something the plasterer should have know and addressed before replastering the wall?

no.
evidence of hygroscopic salts are best detected only after wall coverings have been applied. unless of course the homeowner was aware of the situation prior to plastering, i.e. when the original plaster was in place.

gday2uk · 15 Nov 2008

How about a nice thick heavily patterned wallpaper? You could make it a 'feature wall'

roughcaster · 15 Nov 2008

noseall said:
noseall said:

Reginalddean said:

Is this something the plasterer should have know and addressed before replastering the wall?

Click to expand...

no.

Click to expand...

evidence of hygroscopic salts are best detected only after wall coverings have been applied. unless of course the homeowner was aware of the situation prior to plastering, i.e. when the original plaster was in place.

Both the plasterer and you will know the next time though Reg'. It's always a gamble using gypsum plasters on old brickwork/stonework without "at least" scratch coating them with sand,cement w/proofer first.. One good thing about it though, if your wall gets any worse in the future, eg: paint blistering up, patchy areas appearing on the surface etc, at least you'll know how to cure it,, by taking it all off and starting again. Hope it doesn't come to that but???

Roughcaster.

Symptoms · 15 Nov 2008

Reginald - leave it a bit longer, paint it with stain-block, them emulsion. If it shows through the decoration do as other have suggested - remove & start again. If it doesn't ... result.

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Fresh Plaster Showing Damp?, Chimney Breast with Photos!

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