I have a custom-made outdoor fireplace where the sides and top are lined with firebrick. One of the bricks on the "ceiling" has come out, and I'd like to just reattach it somehow. The ceiling if flat at about a 20 degree angle to horizontal. I tried using heavy-duty construction adhesive on the top and mortar on the sides, but it didn't last a day.

As a fallback, I might just use a long piece of angle-bracket to hold the brick in place. The bricks are not visible or easily reachable from outside so I'm not worried about it getting touched, but I'd prefer to just reattach the brick if possible.

What's the best adhesive to use on brick that's exposed to winter cold air and extreme heat?

  • Is the box ceiling flat or arched? Is the mortar disintegrating due to heat?
    – isherwood
    Dec 5, 2018 at 19:24
  • @isherwood it's flat at about a 20 degree angle. Good question about the mortar, I don't know but the other bricks seem tight (we don't use the fireplace that much)
    – D Stanley
    Dec 5, 2018 at 19:25
  • You've encountered the reason that brick ceilings are typically arched, and therefore self-supporting. I'd look at something like you describe, with bars to carry the brick. My wood-burning fireplace has something similar as a heat baffle--an angle iron slides in under the firebrick.
    – isherwood
    Dec 5, 2018 at 19:35

1 Answer 1


On fire box repairs I use fire clay. It can handle the heat and if tightly packed and dried prior to use it should hold. This is the only thing I have ever tried over the years, there may be products out there that can tolerate the heat but I just use fire clay.

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