Cleaning soot off brickwork before repointing and plastering

[roofmog]

Hope I've put this in the correct section. I'm renovating the open fireplace in my cottage, intending to plaster over the existing brickwork. As I have started to remove the decades, if not centuries, of soot, it has become obvious that a certain amount of re pointing is going to be required as well. Given that the appearance of the brickwork is not important, how much of the soot do I need to remove in order to get a suitable surface for the mortar and plaster to bond to?. Also are there any cleaning products that I should avoid that might interact adversely with mortar and plaster bonding.

 

[Alastairreid]

I would clean as much of the soot off with a wire brush then give it a coat with an sbr cement slurry.

Let it dry.

Then..

Scratchcoat 4-1 cement render with added waterproofer.

 

[roofmog]

Thanks for the advise. Would there be anything to be gained by PVAing the surface first

 

[Alastairreid]

The SBR is a superior alternative to pva.

 

[roofmog]

Thanks for the reply. As I understand it, the sbr cement slurry would provide a stable surface for plastering, however would this also be suitable for the areas where I need to replace missing mortar around the bricks?

 

[Alastairreid]

Yes.

 

[roofmog]

Thanks... I guess I'd better get going with the wire brush

 

[ree]

Dont use any gypsum plaster on the cleaned up brickwork, even when SBR'ed - use sand and cement or backer board.

 

[roofmog]

Returning to this project after an enforced break for personal reasons. What ratio of SBR to cement should I use for the slurry?