Rendering/Plaster in a hot area

[diy_darren]

I plan to render, then plaster, the inside of my chimney around where the log burner sits.

Am I OK to use standard mortar for the render layer, or should I be using fire cement? Depending what I use for the mortar layer, should I then use anything special for the finishing plaster layer?

 

[noseall]

use a lime based render only. rub it up with a polyfloat and nap it with a sponge.

forget skimming as it won't last.

wet the masonry thoroughly before applying the render, as it will give the best chance of the render staying put.

don't mess about with the render too much once applied. apply one coat only.

 

[diy_darren]

Lime based render is just a sand/cement mix with lime added? What part mix would you recommend - 4:1:1 ?

What does nap it with a sponge actually mean?

 

[marshman]

you be better of with 6.2.1 2 being lime or using lime putty, float in smooth with a plastic float filling any little holes
nap it with a sponge means rub it over lightly with it using then sponge like a float.

 

[diy_darren]

I gave this a go today on a 1m squared section and have just pulled it down because it's cracking really badly.

Like a fool I thought I remembered the mix and now I come back to this thread I see I mixed at 4:2:1 when I should have used 6:2:1 Is getting the ratio right going to prevent such bad cracking on my next attempt?

I brushed the wall down with a wet brush, then soaked it with a sprayer. Left it for 10 mins and soaked it again. Left it for a few mins and then applied the mix. Got a covering of about 12mm in most places.

 

[marshman]

your brick work is very dry, if you scrape on a thin scratch coat first and let this dry this will help stopping the second coat cracking,
you could even use 6.1.1or 7.1.1 the problem doing these areas is if the mortar is to hard it cracks and craze with the heat.

you could use this as its made for the job.http://www.hotline-chimneys.co.uk/products.asp?partno=HPS

 

[noseall]

USE PLASTERING SAND!