Concrete driveway exploded under my chimney!


 
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Greg Caesar

New member
Anybody else ever have this happen to them?

I have a wood deck, so when I light my chimney I do it on the driveway. Never a problem before. But last weekend, the top layer of concrete under the chimney exploded, shooting concrete pieces up into the chimney, scattering coals, and tipping the chimney! Fortunately, I always light the chimney well clear of anything (fence, cars, my wife, the 2-year-old, etc). So the only consequences were a Weber-Chimney-Shaped driveway scar and a late start on dinner.

We had heavy rain throughout the week here in Houston, and my driveway has a large crack near where I set the chimney. My theory is that water trapped in the concrete heated to boiling causing the explosion.

Here are some picures:

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Anybody else ever hear of this?

Greg
 
I think I'm going to "take photo sharing to the next level" and order a coffee mug featuring the picture of your driveway.

Bill
 
Sorry to hear about your damaged driveway.

I always use my 20 year old Smoky Joe when lighting the chimney for the 22" grill or WSM. If you cruise craigslist, you can pick up used ones for $10.
 
That is pretty wild. I think you have a good working theory there about the water. I know water freezing will do the same in the winter around here.

I also know that rocks will explode in a fire. Some friends had a bon fire and had rocks around the fire pit and one of them exploded.
 
By coincidence, I was lighting the chimney for my brand new Smokey Joe Platinium. I guess I placed the chimney on my driveway from long-standing habit for my WSM.

I'll light the chimney in the SJP for now on obviously ...

Greg
 
Greg,

Can I post a couple of those photos in the How to use a chimney starter article? It would help others learn from your experience.

Please reply is OK.

Thanks,
Chris
 
Sorry about your damaged driveway.
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I usually set my chimney starter on 2 bricks set on their long, narrow sides and a few inches apart. My theory is that this facilitates airflow from under the chimney and up through the coals, helping the briquets to preheat and light a little faster.

Rita
 
You could be right, but I had this happen once w/ no cracks or rain. I thought it might be a pocket within a lump of the charcoal itself (lump, not briquettes). But maybe it was in the concrete.
 
Sorry to see your driveway--

I always put my chimney on the grill grate until it`s ready..

Was that the concrete or a seal coat layer?
 
Wow! Sorry to hear about that.

I have been using an older metal umbrella stand I have tucked away...and I only did that to avoid the black marks on my concrete patio...now I am glad I did!
 
I had read on this site that this could happen and therefore, I never did put it on my concrete. It is amazing how hot a chimney will get. I have a gravel driveway with a concrete pad in from of the garage. I put the WSM on the concrete (on a drip pan), but I lite the chimney off on the gravel. The other benefit to putting the chimney on the gravel is that it gets it further away from my house.
 
Good learning experience.

I used to light the chimney on a paver stone until it cracked. Now I light the chimney in the grill.

We all learn the hard way.
 
Wow. I agree with the heat and concrete issue (particularly the info at the link Doug posted). Portland cement concrete (normal concrete) is not rated for high heat applications. However, I wouldn't expect that type of explosion on a normal slab from a charcoal chimney assuming the heat directly on the concrete is not as hot as a cutting torch. I would expect cracking, crumbling and other breakdowns over time though. That makes me think you had a couple of other things working against you in this case. I think the thin surface layer on top of the slab is the key. It is/was thin and probably not bonded very well to the base slab. If your driveway didn't have that top layer, it probably wouldn't have failed as dramatically. Trapped moisture could have been an additional contributing factor.

What is in that top layer?

Mike
 
I'm not so sure about the makeup of the driveway. It is original to the house - 1976. Several other homes in the neighborhood have already repaved driveways based on cracking / shifting over time, though I suspect I'm the only one to blow up a portion of their driveway with a hobby.

Greg
 
I hear a lot of lamentations over your driveway but I'd be proud! That hole in your driveway is a badge. Display with pride!

Oh the tales you could tell. Think of your grandchildren!

"...way back in the spring of oh-seven - there I was..."



Donald

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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by MikeP:
What is in that top layer? </div></BLOCKQUOTE>

That top layer is just normal concrete. That's what you get when you float a slab of concrete. The aggregate (stones), are pushed just below the surface and you get a really smooth top finish.
 
I have stained the concrete patio behind my house, but it's never exploded on me. I use my 22.5" kettle charcoal grate to start the chimney starter now. I find that the additional airflow under the bottom of it helps light it a little faster.
 
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