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Heat resistant render formula required

Discussion in 'Plastering and Rendering' started by Shetland Phil, 12 Sep 2021.

  1. Shetland Phil

    Shetland Phil

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    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.
     
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  3. RandomGrinch

    RandomGrinch

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    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.
     
  4. lostinthelight

    lostinthelight

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    Last edited: 12 Sep 2021
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  5. Shetland Phil

    Shetland Phil

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    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.
     

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  6. lostinthelight

    lostinthelight

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    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?
     
  7. Shetland Phil

    Shetland Phil

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    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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