shadowy outline of cavity blocks on interior walls Ask your questions and find answers on many subjects relating to plastering and dry lining

[bibien]

Can anyone advise me about the sudden appearance of the outline of cavity blocks on my interior lounge walls. The outlines look like shadows on the walls and are dusty grey.

I want to redecorate and do not know what to do to ensure this problem does not happen again.

Advise would be very much appreciated.

Regards

Bibien

[plumbbob]

Most unusual. Is this damp?

[stoneyboy]

bibien,
This is caused by cold bridging by the mortar around the blocks. The only solution I can suggest would be to have your cavities filled.
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[bibien]

Thank you Stoneboy for your reply.

The cavity walls are insulated. The house was built in 1985 do you think the insulation may have deteriorated?

Thank you again for the information

Bibien

[stoneyboy]

bibien,
When you say the walls are insulated was this done as part of the build or has CWI been injected at a later date?
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[bibien]

Hello Stoneboy

The cavity insulation was part of the original build in 1986.

Regards

Vivien

[bibien]

Hello

No it is not damp, but have had a lot of condensation.

Another person in plaster and dry lining forum says he believes it is due to cold bridging around the masonry on the blocks.

Thank you for your interest

Bibien

[stoneyboy]

bibien,
In view of the age of your home it is unlikely that clips were fitted to retain the insulation slabs against the inner cavity. It is likely that there is a ventilated gap between the slabs and the outer surface of the inner cavity.
Realistically all you can do is to redecorate the wall as and when the block outlines become unacceptable.
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[bibien]

Hello Stoneyboy

Thank you so much for taking the time and interest in my problem. You have been very helpful and have given me an insight as to the cause.

I have also been advised by BrickPat on another forum to use 2 coats of PVA.
So this ties in with your last suggestion to paint.

Kind regards

Bibien :)

[stoneyboy]

bibien,
I would not recommend PVA, this will leach through any water-based paint and give a variable surface finish.
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[bibien]

Hello again Stoneyboy

What would you suggest I use as a base coat?

Regards

Vivien

[stoneyboy]

bibien,
Clean a small area of the wall with sugar soap solution then apply a coat of emulsion over a small area to see if the block outline grins through.
If it does you will have to seal the wall with an oil based paint - again try a small area with white undercoat.
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