Anna Kettle wrote:
On Fri, 19 Sep 2008 04:39:04 +0100, Rod
wrote:

If you are thinking lime plaster (and that would be expected!), I don't
know. But for gypsum the temperature is quite low and could easily be
achieved round a wood burner.

Well I suppose I am because I've often seen lime mortar used to line
fireplaces and flues. I just looked up the burn temperature and
900degC is mentioned

Well that's probably the source of the confusion then: I regard lime
plaster as pretty much like cement render, and cement of the portland
type needs to be red hot before it degrades. Although it will, as the
back of my open fires testifies: bricks and mortar have been etched away
by heat. Even the cast iron firebacks that went in after I noticed that
have cracked. Hence the need for 'fireproof cement' when constructing
hearths.


`But plasterboard which is gypsum, on a bonfire, goes crumbly very
rapidly. I assume household ordinary plaster is similar.

Again I don't have absolute date but the builders I worked with
recommended render for the space behind the stove, not plaster.