Another render mix question

[Robin]

What mix(es) would suit re-rendering a chimney-breast in a loft please?

It's a Victorian terrace with the original render loose. Smoke test shows no leaks yet into the loft, but I've been told gas fitters may still not fit/pass gas fires unless the render is in good nick. And re-doing it will cut down on the dust in the loft.

The original stuff seems to be quite light compared with modern sand/cement render or haunching; and its full of small bits of glass, broken brick and other stuff; but its harder than the lime mortar between the bricks. Photos here if they are of any use.

[Andrew Gabriel]

chimney rendered in the loft. I wonder if it was done later due to leaks? I've seen 1950's houses with internally rendered chimneys, but then it's plain sand and cement render as you'd expect in the 1950s.

You can't use gypsom based plaster because the chimney breast will be damp due to water ingress down the flue and no damp proof course in a victorian chimney. It would have to be lime, or sand and cement.

I would also say it doesn't need to be there at all, providing the pointing is in good condition, but I don't know if there are specific regs for gas flues that would require it. BG fitted a gas fire for me in 1986 in a victorian house without any render on the chimney in the loft, but gas rules have changed since then (most notably in 1988).

BTW, don't go raking out any significant depth of pointing from the chimney without first looking down the flues to see how much is still left on the insides. Over the years, you might find half of it has been washed away inside particularly on the first vertical part down to the first bend, and if you rake out the outside, there's nothing left holding up the pile of bricks formerly known as the chimney.

[Robin]

Many thanks for all that.

Probably my misunderstanding. I've checked with the relevant neighbour and she says the fitter may have meant that if it's already rendered then the render needs to be in good nick. That'd fit with your suggestion it was rendered to fix past leaks.

Thank you again. I'd not have enjoyed that opportunity to learn from my mistakes.