Heat resistant plaster

[electricianid]

Hello,

I've just had an inset wood stove fitted and after three lights, some of the (gypsum) plaster has cracked and fallen away in two or three places. I was looking at re plastering in something like Vitcas or Everbuild heat resistant plaster but am now thinking that a lime and sand finish would suffice. Do any forum members have experience with either lime/sand or one of the above brands in a similar setting, if so I would be delighted to hear about it.

Regards,
Ian

 

[steveb]

we did sand/lime over a hardiebacker type cement board, behind a freestanding wood stove. Been fine for 8 years but sure if the use case is comparable

 

[paulc]

I have an inset stove, and the chimney breast can get extremely hot - Have seen it up at around 120° just above the stove :shock:

Base coat was with the Everbuild heat resistant plaster (it is actually a High Alumina Cement) and topped with a lime plaster. If I were to do it again, I'd use lime all the way. Do have a couple of very fine hairline cracks, aside from that, the lime plaster is standing up to the heat very well.

Just let the plaster dry naturally and don't try to force it by lighting the fire too soon.

 

[electricianid]

Thanks for valued replies, I will go with Everbuild and lime as paulc has successfully used it. Leaving it to dry thoroughly is certainly good advice, I wonder if high alumina lime is available?

 

[paulc]

If you do use the Everbuild or Vitcas stuff, don't put as much water as it says on the packet in the bucket. Start with about a third or quarter lass, and add a bit at a time until you get the consistency required. Don't overwork the surface or try to get a smooth polished finish - If you're putting lime over the top, you'll need a rough surface for the top coat to stick to.

When I used the Everbuild "plaster", I followed the instructions and had a very sloppy mix, overworked the surface and ended up with a polished finish. On the advice of Mike Wye, it was primed with DG27 before the lime top coat went on.

 

[TheForge]

Thanks for valued replies, I will go with Everbuild and lime as paulc has successfully used it. Leaving it to dry thoroughly is certainly good advice, I wonder if high alumina lime is available?

You could make a high alumina lime render by choosing a sand with high alumina content, glass sand or the like. I’m not sure how this would perform though as those sands tend to be very fine and may need blending with a coarser aggregate.

Natural Hydraulic limes will also contain some alumina impurities, the source of the limestone dictating how much and the grade of the NHL indicating the amount of impurities (silicates, ferrites, alumina etc).

 

[electricianid]

If you do use the Everbuild or Vitcas stuff, don't put as much water as it says on the packet in the bucket. Start with about a third or quarter lass, and add a bit at a time until you get the consistency required. Don't overwork the surface or try to get a smooth polished finish - If you're putting lime over the top, you'll need a rough surface for the top coat to stick to.

Thanks for the tip paulc, I will relay this information to the plasterer if I go with either of these although am leaning toward an NHL plaster.

 

[electricianid]

You could make a high alumina lime render by choosing a sand with high alumina content, glass sand or the like.

Where would one go to obtain high alumina sand?

 

[TheForge]

Good question. Sand blasting sands are high in alumina. Search sand blasting sand suppliers maybe?