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submitted 2 months ago* (last edited 2 months ago) by redlemace@lemmy.world to c/dull_mens_club@lemmy.world

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Gonna be a part of my grill table so I can use cast iron cookware. Gotta smoothen a few bits and have not thought much about how to mount it (probably two iron bars under it)

edit: Thanks for all the remarks. I had some of the concerns myself (but decided a test-drive could confirm/take away those) Now I'm not all that sure if i'm gonna use it or make a different solution. Also due to the weight. It's something like 30Kg. The kamado is another 100Kg plust the table itself ...... it's getting heavy.

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[-] Lemmyoutofhere@lemmy.ca 30 points 2 months ago

Not worried about concrete exploding from the heat?

[-] redlemace@lemmy.world 9 points 2 months ago

not really. Tried it on a smaller scale but heated it up real good

[-] NaibofTabr@infosec.pub 57 points 2 months ago* (last edited 2 months ago)

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?

[-] redlemace@lemmy.world 5 points 2 months ago

I did not use rebar reinforcements. Iron expands more than concrete, felt like it could destroy it from the inside out

[-] NaibofTabr@infosec.pub 2 points 2 months ago* (last edited 2 months ago)

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.

[-] ITGuyLevi@programming.dev 13 points 2 months ago

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.

[-] yakko@feddit.uk 5 points 2 months ago

Maybe they used refractory concrete?

[-] BlackVenom@lemmy.world 3 points 2 months ago

Should use reheatable concrete IMHO.

[-] yakko@feddit.uk 2 points 2 months ago

I dunno much about it, but don't they make pizza ovens with that stuff?

[-] blargh513@sh.itjust.works 3 points 2 months ago

Nope.

[-] Angryhumanoid@fedinsfw.app 4 points 2 months ago

I was wondering that myself. I assume there are methods for avoiding that? Concrete type, and reducing bubbles, etc?

[-] Lemmyoutofhere@lemmy.ca 14 points 2 months ago

It’s the moisture trapped in the concrete that is the issue.

[-] Angryhumanoid@fedinsfw.app 7 points 2 months ago

Ohh that makes sense, my brain went to air pockets instead of moisture pockets.

[-] Mpatch@lemmy.world 3 points 2 months ago

Nah, the best would probably be to line it with fire brick.

[-] expatriado@lemmy.world 11 points 2 months ago* (last edited 2 months ago)

i use firebricks for burning charcoal or wood, a bit more expensive than regular bricks, but won't crack under heat stress as easily. If that is just a place to rest hot utensils and pots, it is good as it is, enough air gap

[-] prettybunnys@piefed.social 7 points 2 months ago

That looks pretty porous, if you put coals on that (??) so you can cook on the grate you might find it ‘asploding, especially if any liquids spill on it while grilling.

your setup is neat tho

[-] mastod0n@lemmy.world 5 points 2 months ago

I like it! How did you get rid of the air bubbles to prevent expansion/burst?

[-] agedcorn@lemmy.world 12 points 2 months ago

Judging by the texture on that concrete, they didn't.

[-] redlemace@lemmy.world 1 points 2 months ago

I shook and knocked it a lot until it stopped bubbling

[-] solidheron@sh.itjust.works 5 points 2 months ago

Can you hear treat concrete? Like can you burn it in a bon fire to see if it can survive heating

[-] NaibofTabr@infosec.pub 1 points 2 months ago

This would definitely be a valid way to test it, though you'd want to fully support it not just throw it on top of some burning logs. Maybe build a fire on top of it?

[-] solidheron@sh.itjust.works 2 points 2 months ago

Yeah I was thinking it be better to bury it

[-] fluxx@mander.xyz 4 points 2 months ago

Don't know if you're aware, but there is a video om yt about aircrete, which is a diy process of mixing concrete with xsantan gum introducing air bubbles. It has better heat insulating properties and may be more safe. Ive not tried it, but will experiment in the future. https://youtu.be/z4_GxPHwqkA

[-] DarrinBrunner@lemmy.world 2 points 2 months ago

You needed to stir the vibrator around in there some more.

[-] Cheebus@lemmy.world 7 points 2 months ago

instructions unclear: used the wife’s hitachi, she’s not happy

[-] YiddishMcSquidish@lemmy.today 6 points 2 months ago

Still worked!

[-] DarrinBrunner@lemmy.world 2 points 2 months ago

Huh. My wife usually enjoys it.

[-] newton@feddit.online 2 points 2 months ago* (last edited 2 months ago)

Use safety glasses bij heat expos. concrete . Wounds don't heal easy. Stay safe.

this post was submitted on 21 Jul 2026

199 points (98.5% liked)

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