this post was submitted on 21 Jul 2026
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Not worried about concrete exploding from the heat?
not really. Tried it on a smaller scale but heated it up real good
There is actually a genuine concern here, because a larger piece will hold water inside the concrete longer, so your smaller test may not be representative for the behavior of the larger piece.
You can test it by placing it on the ground, somewhere where it's fully supported on the bottom and heat won't be an issue, and fill it up with charcoal and get it hotter than you would for normal use. Try to heat it gradually so it doesn't stress fracture. If it doesn't crack, the heat should drive out any remaining water. If it does crack, you just saved yourself some trouble.
I would also suggest doing something to support the bottom of the thinnest area when you mount it. It may be more fragile when it's hot. Or... is the concrete reinforced with anything?
I did not use rebar reinforcements. Iron expands more than concrete, felt like it could destroy it from the inside out
Possibly, and yeah rebar might be overkill for this. I was thinking more like a steel mesh near the bottom, or fiberglass. You can get cut fiberglass for concrete fill like this:
https://www.amazon.com/Fiberglass-Concrete-AR-Glass-Chopped-Reinforcement/dp/B0FG2JGN48
This makes the concrete stronger and lighter and increases temperature stability, and it's pretty cheap but it does add some complexity to the casting. I don't recommend handling glass fiber with your bare hands - glass splinters suck - and you should also wear a filter mask (hopefully you're wearing one while mixing the concrete anyway because silicosis also sucks). I found this video which shows the process for making a countertop with glass reinforced cement:
https://www.youtube.com/watch?v=pYqVPdbi6mM
They use an epoxy-based Portland cement - you would not want to do that because the epoxy might outgas when heated by charcoal, and you wouldn't want to do the urethane finish coat for the same reason, but otherwise you should be able to follow the same process with water-based concrete.
I haven't actually tried this myself, but I think having the fiber mixed in would be especially good for keeping the concrete stable over repeated cycles of heating/cooling expansion and contraction.
All that said, I think you should temperature test the piece you've already made first before investing time/money in doing something more complicated. If it works then it works.
Please be careful man, I didn't even know it would happen until I was burning stuff on a concrete slab and suddenly had chunks of concrete flying out at me. Definitely do what you feel best, we are all people with our own experiences, but be safe my dude. It does look kinda cool.
Maybe they used refractory concrete?
Should use reheatable concrete IMHO.
I dunno much about it, but don't they make pizza ovens with that stuff?
Nope.
I was wondering that myself. I assume there are methods for avoiding that? Concrete type, and reducing bubbles, etc?
Nah, the best would probably be to line it with fire brick.
It’s the moisture trapped in the concrete that is the issue.
Ohh that makes sense, my brain went to air pockets instead of moisture pockets.