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Old 08-21-2008, 08:41 PM   #1
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Fire Pit


Hi there. I was wondering if anyone can help. My husband and I just had a concrete slab set in our yard to have a patio in addition to our deck. We used the side of the fire pit as 1 wall and then made 3 additional walls of a fire pit with cement retaining blocks. I have now heard that if cement gets hot it can pop and crack. Is this true? Will putting additional retaining blocks up against the concrete help? The fire pit is big enough that the fire would be about 8-12 inches off of the side of the concrete. Help!

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Old 08-21-2008, 09:07 PM   #2
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Fire can degrade concrete if it gets hot enough, but it probably won't happen instantly. It could take years before it ever becomes an issue, if ever. What you're describing is a little hard to picture though.

If your slab is not part of the fire pit, I wouldn't be too concerned.

Fired clay bricks and refractive mortar are often used for fire pits, just because they take the heat a little better.


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Old 08-21-2008, 09:49 PM   #3
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Direct flame will cause a problem with concrete products. Heat is a problem with some concrete because of differential thermal expansion of the aggregate. Any areas subject to direct flame should be faced with fire brick.
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Old 09-01-2008, 01:28 PM   #4
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I think a decorative facebrick is the way to go. Could enhance the design and protect the concrete from cracking, etc.
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Old 09-01-2008, 01:41 PM   #5
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Facebrick is not much better than concrete. Use firebrick.
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Old 02-03-2009, 01:30 PM   #6
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I built a firepit on on existing concrete and it popped after one fire...could I lay firebrick on the bottom of the pit to protect???
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Old 02-03-2009, 01:39 PM   #7
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Yes you can, but you have to use firebrick AND refractive mortar. The sides and bottom of any fire pit should be made this way. If standing water after a rainstorm is an issue then leave small holes here and there, or drill a weep hole through the firebrick. Simply dry laying the firebrick will still allow a major amount of heat into the concrete.
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Old 02-03-2009, 02:54 PM   #8
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Quote:
Originally Posted by phxccw View Post
I built a firepit on on existing concrete and it popped after one fire...could I lay firebrick on the bottom of the pit to protect???
Ayuh,..

I have a Firepit, which is merely a big steel Ring, 3/8" thick, 3' 6" diameter,+ about 15" tall....
Kinda like a heavy piece of pipe, lain on end...

I have nothing But a concrete patio where it's at,...
I took a bunch of chimney bricks from a recent tear-down,+ layed them out flat, all sides just touching, in a pattern that's slightly larger in daimeter than the steel ring,..
I then have 4 more of these bricks to hold the steel ring 2" off the bricks for draft...
These are just plain ole Junk Bricks,...

Over the last 3 years, I've moved this assembley around the patio several times to several places,...
Other than replacing a few of the Bricks every now,+ then,...
I've had No stains, No spadling, just No Sign of where it's been used....
During this time,...
I've burnt Most of a 100' Poplar tree that I had cut down...
That's Alota Fires,.. Hot fires too....

Last edited by Bondo; 02-03-2009 at 02:57 PM.
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Old 02-03-2009, 03:18 PM   #9
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Thanks for the help guys, I was a little shocked when the concrete pop'd and cracked. I had no idea concrete would do that, since the brick store said I could just lay it on the slab without any issues. Could it had been an air pocket or lighter fluid that got into the concrete pores???
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Old 02-03-2009, 03:54 PM   #10
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Concrete is not the problem. It is the aggregate in the concrete that expands at a different rate than the paste. Some parts of the country it isn't much of an issue, like here, but some it is. It depends upon the aggregate used.

Regardless, you should NEVER have direct flame on concrete. Old common brick (solids) usually will work as firebrick.
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Old 02-03-2009, 04:09 PM   #11
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common brick (solids)??? So I don't need fire brick just as long as it's solid brick? Sorry I'm a newbie.

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Concrete is not the problem. It is the aggregate in the concrete that expands at a different rate than the paste. Some parts of the country it isn't much of an issue, like here, but some it is. It depends upon the aggregate used.

Regardless, you should NEVER have direct flame on concrete. Old common brick (solids) usually will work as firebrick.
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Old 02-03-2009, 04:32 PM   #12
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Ayuh,...

Plain ole red building Bricks.....

If you Have to use the 1s with the holes in them,...
Build a small fire,+ use it's ashes, or some sand, to fill in the holes...

Once you have a small ash mound, the heat forced Down diminishes Alot...
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Old 02-03-2009, 04:40 PM   #13
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If it is outside where you won't burn your house down, soft commons are fine. Modern cored brick are not as good. To do it right use refractory brick, i.e. fire brick.

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