Strategy for insulating external wall around fireplace

[Jahouli]

Sorry larry, I should have mentioned I found the 25mm single pass optimistic. I did two passes of 10-15mm each. I threw a few choice curse words around trying to get 20mm to stick, before I gave up and went thinner.

 

[larry]

One more update...

So I also used the Prooftherm screed... I'd used a number of bags, didn't order enough so bought some more. Second delivery there were some bags that were grey in colour, I hoped because of the aggregate. Everything else had been white so far.

Turns out it was all cement based. The white stuff is white cement (?) and the grey stuff ordinary Portland cement based.

I should have read more carefully the website. It does mention it's cement.

Anyway, sigh. It's only the hearth so hopefully it isn't going to be a complete disaster as I really cannot bring myself to pull it all out again.

But anyway. Yes. Cement.

The plaster is definitely only Lime though from a careful read.

 

[paulc]

If it is any consolation, I used a high alumina cement "plaster" around my stove. Finished it off with a lime skim, then polished it.
A few hours with the fire lit will see the temperature of the chimney breast getting well over 100°C (seen 180°C at one point). Plenty hot enough to drive any trace of damp out.