Plastering over soot

Hello there, yeah what you heard is correct (from my personal experience) i once bonded over soot and skimmed it and when it dried it looked fine but when mr decorator painted it it there was plenty of yellow stains comin through!
best way to do it if possible is dot and dab 9.5mm board over it, but i`d give it a quick brush a wet brush to get the excess dust off the wall!
otherwise get me to do it haha!
hope i was helpful!
mike.

 

I would remove the loose soot the use thistle bond-it over it. that will stop it coming through.
Im down south, where are you?

 

soot will contain aggressive nitrates and chlorides which are hygroscopic salts. These salts are also common in rising damp probs. They may come to the surface if using a gypsum plaster. Therefore treat same as damp - sand and cement or a renovating plaster.

 

near Exeter mate

 

clean down the soot pva it and then plaster with thistle dri coat or youll have one hell of a problem with efflovesence comming through (salt) and did i spell it right??

 

"effloresence comming through"

No mate - effloresence is sulphate which is the white fluffy stuff. Soot contains hygroscopic salts - you wont get the white sulphate coming through. Instead you get what appears to be round damp patches randomly on the wall. The chlorides and nitrates are hygroscopic in that they take the moisture from the air when they come to the surface resulting in the damp patches.

 

Any wall that has effloresence should get a treatment with an anti-sulphate salt neutraliser first before replastering. By the way - Thistle Dri-Coat is a type of renovating plaster just like Renderlite and Limelite with better thermal properties than s&c render.