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We are planning to lay a tile hearth in our fireplace but unfortunately, the concrete subfloor is quite uneven, see pictures. We have had this fire opening widened, so the black damp proof course is is where the old internal brick course was. There is only a small 1 inch x 5 inch area is the very corner where there is a void.

How can I create a flat even surface ready to lay tiles that is suitable for use under a wood burner?

I had considered using a Hardie Backer (concrete board) to cover this entire area, but this would add too much height. So if there is another solution I would like to try something different.

Would I be able to level this out with concrete?

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  • have you done any research? ... this is covered by many tutorials on the web
    – jsotola
    Sep 15 at 19:39
  • How deep are the depressions? It may just be a matter of an initial skim of tile mortar.
    – isherwood
    Sep 15 at 21:04
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    A 20 amp grinder and the appropriate wheel. Tiling method that is suitable for use under a wood burner is the part I'm unsure about.
    – Mazura
    Sep 16 at 9:33
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    I wonder how a 1/2" thick cement board would take up so much space in the firebox that it would be precluded from consideration.
    – FreeMan
    Sep 16 at 15:32
  • As I look at the picture again, I notice that the bricks are veneers or tiles. Is all of this good for use that closely around a wood burner? It looks like a fairly small space to be installing a wood burner...
    – gnicko
    Sep 27 at 13:07
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You'll want to research/google "self-leveling concrete". It's a special mixture of concrete and polymers that you mix up and pour onto a surface like you have and it levels itself off and dries as a smooth, level, and hard surface. Perfect for setting tile.

While it's bad form to recommend specific products here, you should be able to find a selection of brands and package sizes at your local BigBox store (and most hardware stores.) Essentially, you mix it up, pour it out, and wait for it to dry. They also sell it as a pre-mixed compound which you may find easier to work with and possibly available in smaller quantities.

You'll want to fill that void first.

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    Be sure to pick one that specifically indicates that it's suitable for use in a fire box. If you can't find that labeling on any of the brands/types available locally, I'd suggest calling the manufacturers to ask them - they'll know better than anyone. You may have to order online or direct from a manufacturer or go to a specialty store instead of a big box store.
    – FreeMan
    Sep 16 at 15:26
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    I have never seen a self-leveling concrete rated for 1000F. I would not use this in a fireplace.
    – DMoore
    Sep 16 at 18:48
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For the inside of the fireplace you will use a "Stove and Fireplace Cement" or may be called a "High Temp Cement". You will need to read a few different products as some are more suitable for a skim coat and crack repair and others are more suitable for thick applications.

For the rest... Just a high quality modified (latex) thinset. If you are tiling outside the fireplace you should flatten/level your surface with a thin coat of the modified thinset. Give it a few hours to harden a bit, then lay your tiles (adding thinset to the back of them of course).

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  • Sorry I don't have recommendations on the cement. It has been 15 years since I have redone the inside myself. There are others that can suggest things. I have tiles the outside of many fireplaces that look just like yours.
    – DMoore
    Sep 16 at 18:49

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