How to prevent soot stain and odour bleeding through dot and dab plasterwork?

by Victoria
(Rugby)

Hi Paul

I don't know if you have had experience of having to dot and dab plasterboard and plaster over soot damaged areas where chimney breasts have been removed. If so, are you able to provide clarification on the following situation, I have researched online extensively and have come up with conflicting information:

As part of major renovation work on my house I have removed 4 chimney breasts.

Could you please let me know whether you are able to advise on the best method of removing the soot residue on the brick wall areas that have had the chimney breasts removed and are coated with 100 years' worth of soot. Also, what products should be used to seal those areas prior to dot and dab insulated plasterboard being fixed. The reason for this is to prevent the leaching through of the soot and to eliminate the smell of soot.

Also, the chimney breast areas in the attic space will be left bare. Should they be treated in the same way as for the chimney breast areas that are being dot and dabbed.


Thanks very much.


Victoria


Answer
Hi Victoria,
I can tell you what I have done in the past - to overcome the issues you mention, but I am not giving you specific advice.

Firstly I scrape/brush off whatever I can.

As you say the soot will definitely leach through - so I apply 2 or 3 coats of diluted PVA.

This has always worked for me:
a thin 1st coat (to really penetrate).
I let fully dry before applying another thicker (less diluted 2nd coat)
let dry and if I'm wanting to be really sure - I apply a 3rd coat with some sand in to aid future plaster application.

The loft area, if possible I'd think about leaving it to breathe!

But that is what I have done....
…. you must do what you feel is right based on your own research for your individual house needs.

Paul

Comments for How to prevent soot stain and odour bleeding through dot and dab plasterwork?

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Feb 07, 2022
 helpful thanks
by: rory

I am going to take this approach and dot and dab the wall where the chimney has been removed
Feb 07, 2022
 How to prevent soot stain and odour bleeding through dot and dab plasterwork?
by: Victoria

Thanks for the info, Paul. This was the solution I was opting for. I'm going to do 1 or 2 coats of PVA, as you suggest, and then another 1 or 2 coats of SBR.

I've already started scraping off the worst and have then used HG Spray, which has lifted another layer off.

To try to eliminate the smell of soot I'm going to use sodium bicarbonate and white vinegar. I've used this combination to remove a strong smell of diesel from the inside of a shipping container and it did the job really well - nearly a year later and the smell hasn't come back.

When the plasterers come to dot and dab I'll make sure they avoid the soot-stained areas.

Hope I'm doing the right thing 🤞🤞🤞, will let you know one way or the other in a few months time.

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