Render for fireplace.

[davecooper]

I am going to render the inside surfaces of a fireplace prior to getting an inset gas fire fitted. This is to give good gas tight surfaces so the combustion gasses go up the flue without any leakage paths through the old brickwork. What sort of sand/cement mix should I use here?

 

[hotrod]

Are you not having the flue lined? All well and good rendering the fireplace chamber (5:1 will be ok) but will not ensure flue is tight all the way up.

 

[davecooper]

The flue is already lined. The flue was relined for the previous gas fire which had been in place for about 10 years. We used to have a back boiler which has now been replaced with a combi. The old fire had to go along with the boiler.

Once everything had been removed, I was amazed how many potential leakage paths there were from the fireplace to the rooms both downstairs and upstairs. I'm glad I now have a chance to seal everything up properly.

 

[Karis]

There is a big risk it will crack up if you use a straight sand/cement render & where high heat is involved, you need to use a heatproof render. Vitcas make one but it's expensive; an alternative is to use a sand/cement/lime mix (5:1:1). For thick applications apply in two coats, make the second a slightly weaker mix.