Crack in firebrick on opening of the oven

Hello all.

I hav a crack in one of the firebricks that’s closes off the opening. It’s deep and appears to be traveling up. Before I put on my custom door ( it will probably cover it up) should I fix it? Chiseling out the whole piece would be hard and might risk more damage. Should I just chisel out the broken part and form refactory cement to it. I don’t know. What do you think. Here’s a picture of it.

(reply EDITED after a good night’s sleep)

Hi Pete,

I can see why you’re concerned. It sounds like this started out small and is getting longer with each successive fire. Have I got that right?

You are better off with one of the refractory silicone products than trying more mortar. Rutland Red is one example. I used this DAP product in my oven interior because of its high-heat qualities.

For your application I’d much prefer that to chiseling out anything — once you start, you’re not going to be able to stop easily and you risk breaking more brick. Since that’s at the base of your opening, it’s supporting all the weight of the brick, the mortar, and the lintel piece above.

It did that because the structure is settling. It may have a little more shifting around to do, but that’s likely to be the end of it. Patch it for your own peace of mind, and install your door, but don’t break any of that brick.

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That is an odd crack.

Not only is it in an area that’s not prone to cracking… but the angle and direction of the crack are not typical. Usually, a crack in firebrick is a Horz / Vert and it’s super straight - not curved as shown in the image you attached.

I’m kinda thinking that brick may have had an internal crack that wasn’t visible during installation.

Either way, as previously mentioned, you can fill the crack w/ a buff-color high-temp mortar. Super Easy! Personally, I’d only want to do this once, so fire up your oven a few more times and use as normal… once the crack is no longer spreading, then fill in the hairline crack.

Fill while the oven is warm and the crack is fully expanded.

Once the oven cools and the mortar is rock-hard, you can sandpaper-away any excess high-temp mortar.

Home Depot


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Thank you both for the great advice. You confirmed what I was thinking of doing. It’s always good to get a second opinion. I appreciated it.


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