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Swine Spectator
07-29-2012, 10:54 PM
Tonight I was going to practice making chicken lollipops. I filled my chimney with Outdoor Gourmet charcoal (from Academy Sports) and lit it. I went inside to work on the lollipops. When I came back out, my chimney was laying on it's side and lit coals were spread over a three-foot radius. Upon closer investigation, I discovered chunks of concrete mixed with the coals.

There is a circular pit (~1/2" deep) in the concrete that is the same diameter as the chimney. It appears that the heat of the chimney caused the concrete below to explode.

I was able to collect the coals with tongs and proceed with the cook. No one was harmed, but the whole thing kinda freaked me out. What if the kids had been in the backyard?

Has anyone experienced this?

David
The Swine Spectator

mmmmeat
07-29-2012, 10:55 PM
yuppers, same reason they tell us not to weld on concrete...weld metal on top of concrete... with oxy torch specifically... big badda boom

Boshizzle
07-29-2012, 10:56 PM
Yep, that cam happen.i use a cinder block under my chimney or just sit it on the charcoal grat to start the fire.

jlondon
07-29-2012, 11:03 PM
wow, never heard of that happening before. Would freak me out too. I always place my chimney on the firebox grate.

Butt Rubb'n BBQ
07-29-2012, 11:04 PM
Was it fresh or wet concrete. We built a cinder block smoker on a concrete slab and lit a fire in it before it had cured and the thing blew up like a atomic bomb. The expansion of water will blow concrete up.

El Presidente
07-29-2012, 11:10 PM
Yeah I've had this happen too. The concrete can't handle that high of temperature. I start my chimney in the grill now and rest it on paver stones until cool.

Sent from my LG-E739 using Tapatalk 2

NorCalQue
07-29-2012, 11:24 PM
What MMmmmmm-eat said.

I put my chimney on two fire-bricks. If I get another weber grill someday :rolleyes: I'll fire it up on it.

That cinderblock is a great idea, get it even farther off the deck.

Skidder
07-30-2012, 06:11 AM
I would think it's caused by trapped air expanding in the concrete

Wesman61
07-30-2012, 06:23 AM
Yep, I found that out the first time I used a cutting torch to remove a piece of metal from an expansion joint in the warehouse of a company I worked for. A forklift driver hit the angle iron with a fork and bent it upward. I thought "no problem. I'll just cut it off with a torch." Snap, crackle, pop.

Swine Spectator
07-30-2012, 07:18 AM
I have lit my chimney on this slab a 100 times. The slab is >50 years old, but it has rained a lot the past few weeks. Fortunately, I was planning to have it removed in two weeks, so I don't have to worry about the crater.

David

Terry The Toad
07-30-2012, 09:24 AM
Along these same lines... if you are camping, I've read that you should not line a firepit with damp stones. The moisture inside turns to steam and BOOM! :shock:

Bludawg
07-30-2012, 09:48 AM
Concrete is porous and retains moisture, a concentrated heat source will cause the trapped moisture to boil generating steam pockets, as the stem expands it builds pressure hence Ka Boom... charcoal chimney mortar:becky:

bbqbull
07-30-2012, 11:06 AM
Concrete is porous and retains moisture, a concentrated heat source will cause the trapped moisture to boil generating steam pockets, as the stem expands it builds pressure hence Ka Boom... charcoal chimney mortar:becky:

The technical term is called...Spalling.

When my son's pole barn burnt down a few years ago it damaged his concrete floor. So bad they had to break it up and haul it away.

He had just purchased several cases of motor oil and stored it in his barn.

tish
07-30-2012, 12:40 PM
I light my chimney sitting on the grate in my Keg, but have been known to lay it down on the concrete for short periods if I've had to remove the grate to rearrange the lump underneath before dumping the chimney's contents on top. That's pretty scary. Thanks for the warning. :shock:

dadsr4
07-30-2012, 12:50 PM
I light my chimney sitting on the grate in my Keg, but have been known to lay it down on the concrete for short periods if I've had to remove the grate to rearrange the lump underneath before dumping the chimney's contents on top. That's pretty scary. Thanks for the warning. :shock:
If it's only a few seconds, should be no problem. Just don't leave and come back. The OP was gone for a while. Still safer not to though.

colonel00
07-30-2012, 01:27 PM
Sadly I have to admit that I have made this mistake as well. I lit a chimney of lump and left it on the drive for a while. Pop!

FashionBiff
07-30-2012, 05:01 PM
I think I heard this before but wow, good to get the refresher. My wife and I have a PITA Jack a poo so I always light my starter on another grill to keep the pooch safer, I think that is the only reason I keep my aussie grill around.

jestridge
07-30-2012, 05:19 PM
That a question on my safety test is it ok to weld or cut on concreteT/F

Smokendink71
07-30-2012, 05:27 PM
I've actually had this happen also, I bought a flat cast iron skillet at a garage sale and now use it to set my chimney on when lighting, works great

VoodoChild
07-30-2012, 07:22 PM
I got A Smokey joe off Cl just for the Chimney !!! I really Did . :blah::blah::blah::clap2::loco:

mbshop
07-31-2012, 12:24 AM
i thought that was rather well known. a good lesson learned as long as no one was hurt.

MilitantSquatter
07-31-2012, 05:31 AM
Yep... happened to me in 2005..

had been cooking a while, but first (and) only time I ever did that... Popped right in front of me about 8 ft away as I was approaching.. Hot coals went all over the grass and made a small crater in my concrete.... I've been extremely careful ever since.

nucornhusker
07-31-2012, 09:27 AM
I have always placed my chimney on the charcoal grate while heating up, but I do set it on my concrete driveway after I dump the chimney. Is that okay? Or is that a bad idea too?

camben
07-31-2012, 10:08 AM
Happened to me as well. Very scary to say the least.

Arg1129
07-31-2012, 11:00 AM
Though not with a chimney I did this when I was 12. My parents were not home so I took my dad's mini cutting tourch and was melting pennies. The "pop" sent a molten piece of copper flying which stick to the side of my head right near my temple. Needles to say I have a scar from it and am very weary about heat and cement. And yes my dad called me an idiot which I rightfully deserved.

Cack
07-31-2012, 11:21 AM
When I was younger I was torching/melting a penny on the concrete. It exploded shooting melted penny all over the place. I had pieces land inside my eyelid, on top of my nose and even on the back of my ear. The largest nearly nickle sized piece came straight at my forehead but I was luckily wearing a hat that day and it stuck to my hat instead of my face.

I've never burned anything on concrete since ... listen learned

Cack
07-31-2012, 11:22 AM
p.s. This thread sucks without pics