rendering/plastering old sooted chimney wall

[furryboffin]

I am renovating an old stone house built in 1818. I have a couple of questions.

Firstly the old chimney has been removed leaving only the inside of the chimney conduit exposed showing all the sooty bricks. It is thickly caked on and very tough, almost shiny in places.

Can someone tell me the best way to render or plaster this wall? Should I first strip off all the caked soot with machine strippers or sand blaster or something? or can I just render/plaster straight over the soot?

It is an internal supporting wall so I don't need insulation on it, but I would like it to be visible so it does need to be finished nicely.

Secondly I have some concreting which has been done to finish an old doorway and a new window opening and I'd like to render the surface of the concrete to make it a nicer colour with a more uniform surface finish. I have both external and internal parts of this concrete to render/plaster. Can someone tell me what mix I should use to render it both inside and outside? I've never done any rendering before so I'm a total beginner.


Thanks for any help.

 

[noseall]

the sooted bricks will require some graft i'm afraid.

i would go so far as to bolster or power hammer the face off the masonry in order to rid yourself of the contaminated surface.

if it is possible to remove most of the soot, then using an sbr cement slurry + render will go a long way to prevent 'bleeding'.

for a tough render i would recommend using a 3:1 plaster sand and cement mix with waterproofer additive. this can be worked so the surface is pretty tight.

 

[furryboffin]

Thanks for the reply noseall. I'll give it a go, I have a few fittings for my angle grinder that might take the stuff off. going to make a big mess though

could you explain to me what a "cement slurry + render" is. If I wanted to buy it what would I ask for in the DIY shop? Also, did you have in mind to use this mix on the inside of the chimney bricks or on the outside?

Thanks again.

 

[noseall]

you mix in some neat cement powder into the sbr.

this is painted directly onto the affected areas (internally) and whilst still wet or tacky, a sand/cement render is applied to the sbr.

it doesn't hurt to pour a bit of sbr into the mix too.

 

[furryboffin]

Thanks Noseall, I'm still none the wiser as to what "SBR" is. Can you spell it out to my naive self?

Thanks

 

[oldbutgood]

Hi would the finsih not be better in stone, rather than render or plain. I know noseall will know better, but take a look at decopierre on youtube, they seem to have an answer.