Heat resistant render formula required

Shetland Phil · 12 Sep 2021

Hi, I want to render the rear wall of a fireplace, prior to installing a wood burner.
The wall is approximately 70cm x 80cm and I want to apply 45mm of render.
To buy a ready mixed product I would need 66kg at a cost of £170.
Can I simply use sand + cement + lime instead?
If yes, what is the ratio of each?
The rear flue from the stove will be within 5mm of the wall when rendered.

RandomGrinch · 12 Sep 2021

Have you considered using a cement board as backing?
At least it could build up the depth without extortionate costs.
It has been known to be faced with decorative brick slips.

lostinthelight · 12 Sep 2021

Be interested to know why 45mm build up , single or twinwall flue pipe and whats supporting it. some pictures would be good.
https://www.jameshardie.co.uk/fermacellapi/downloads/file/en-GB/06920000002ikMvAAI

Shetland Phil · 13 Sep 2021

45mm is all the space available between the rear wall and where the flue from the stove will join the flexible liner in the chimney. The rear wall currently condensates because it is too thin, I was hoping that adding the render would help (along with the heat of the stove, obviously). Ideally I would add to the outside with blocks, but my expertise and budget won't stretch to this. My previous house had lime cement used exclusively, including around the internal flue as it exited through the apex in the roof. My only concern is getting the ratio right so at this thickness it won't crack.

lostinthelight · 13 Sep 2021

Its not normal to have wood that close to a WB unless the distance is a trick of the camera, are you getting this installation signed off?

Shetland Phil · 14 Sep 2021

The wood will be faced with stainless steel. Installation being signed off by a HETAS fitter. And the answer to my question is?

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Heat resistant render formula required

Shetland Phil

RandomGrinch

lostinthelight

Shetland Phil

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