Is Plaster a non-combustible material?

It is non-combustible. However, it's not terribly heat-proof. I doubt it would last long lining a chimney. I'm not sure if you mean you want to plaster inside the chimney, or plaster around the stove on the chimney breast. If it's the latter then I think plaster is OK.if you want to plaster inside the chimney the advice I have is that a render with lime in it is heat resistant, probably 1:3 hydrated lime:sand or 1:2:9 cement:lime:sand. The first of those mixes is lime mortar and only achieves full strength after 6 weeks or so. The second mix will set more quickly as it contains some cement. I defer to anyone with more experience in the matter,

Andy.

============== Paint may not be non-combustible, depending on what kind of paint you choose. I think there were some bad house fires some years ago caused by painted surfaces which allowed rapid fire spread. Check out the kind of paint you intend using for its potential fire risk.

Cic.

Thanks Andy, I mean to plaster around the stove inside the chimney breast alcove.

Martin.

Thanks Cic, I was looking for heat proof paint today, could only find black from Hammerite. The guy in the shop said any water based paint would be ok.

Martin.

I totally agree with you. I have a similar finsih round my wood burner, with masterboard for teh register plate, and its all fine.

I cautin that even that mortar (and teh bricks used with it) may degrade in the rear of open fires where temps > 1000C are possible.

He means that too. Use lime render with white cement. Something like equal parts of lime and white Portland and some sand bunged in.

There is no way any paint will stand up to any sort of heat. If you want a decor, use tiles.

He is probably IMM then.

All painst are based on organic cacrriers of pigmnents. Few organics stand up to much more than a couple of hundred degrees without discoloration and degradation.

Distempere might work.

Or simply get some artists pitments and add to your cement render,

I have some paint called 'Pot Black' ( nothing to do with snooker ), which is for painting hot engine components, it may be able to cope with the indirect heat on the inside of an alcove. It only comes in black AFAIK. You can get it at an automotive accesories shop. Black may well be your only colour option at that temperature.

Andy.

Any of the oxides (red, yellow, black or mixtures of ) would be ok. Sold as cement additives and originally produced at furnace temperatures.

Are you sure open fires can produce greater than 1000 degC? They can certainly get to several hundred degrees (I would guess 400 to 600) but I am very sceptical that they can get to 1000.

I used to do quite a bit of high temperature chemistry where we started work at 950 and that was a sight hotter than our fire ever gets.