Adding 50mm thickness to brick chimney breast

Discussion in 'Builders' Talk' started by biggs83, Jul 10, 2019.

  1. biggs83

    biggs83 New Member


    I need to add about 50mm of thickness to my chimney breast and scratching my head over how to do it.

    There are 3 reasons for doing this:

    1. To create a recess for the tv mount
    2. To increase to clearance from the stove pipe to the mantelpiece
    3. To create a deep enough recess to the side of the chimney breast for a wood store

    The chimney breast is old brick covered with 2 layers of render and paint. I've heard you shouldn't render over render specially if its painted as it will debond.

    Only thing I can think of is to stick on some 50mm wide breeze blocks and lintels for the fireplace opening and tv mount recess and render over them, making a total thickness of about 70-80mm.

    Just wondered if anyone had a better solution?

    If 50mm blocks are the way to go, whats the best way to anchor them to the existing wall?

    Thanks for any replies
  2. xednim

    xednim Active Member

    metal studs on adjustable brackets covered with fire board
  3. biggs83

    biggs83 New Member

    Building control won't accept pink gypsum board around the fireplace opening, Supalux could work but it is very dear, £200 for a 15mm sheet and I'd need 3 of them.
  4. xednim

    xednim Active Member

    And what is the explanation from BC that it can't be used?
    What about cement board instead?
  5. biggs83

    biggs83 New Member

    Its the paper surface on the gypsum boards, also gypsum boards aren't recommended for areas regularly exposed to 49 Celsius or higher.

    Cement board is a good shout, heck of a lot cheaper than supalux. How would you seal the joints though? Can't use paper tape or mesh as both combustible.
  6. xednim

    xednim Active Member

  7. biggs83

    biggs83 New Member

    Aye that will probably do, thanks.

    Is it safe to have voids though between the studs, what if moisture got in there somehow (say from a leak in the chimney breast) and was exposed to high temps from the fireplace?
  8. xednim

    xednim Active Member

    well, thinking that way we should worry about installing tiles in the bathroom which has chimney breast behind the wall
    cement board is water resist, if you will have any moisture first the plaster will get blown or show dampness that will be indication for you to fix some problems
    working on building sites for a while had only 2 times problems caused by water ingress to the chimney breast- so you have chance 1/500 or less that there will happen something on the back
    if your wall will be like sound box- when tapping with the hand- make few holes and inject fire rated expanding foam (check test of it with blow torch on you tube- surprising! )
    biggs83 likes this.
  9. biggs83

    biggs83 New Member

    Yes was worried about it sounding hollow, expanding foam is a good idea. I'm looking at the siniat dry lining system, which is a 17mm profile. So if I screw on 12mm cement board and then slap two coats of 10mm render, I'll get to the ideal thickness. Nice.

    Actually the house is an old victorian terrace, and there was a leak in the chimney breast which I managed to fix. But goes to show it can happen. There is also some water marks from that leak in the grout between the bathroom tiles!

    Anyway thanks for the advice

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