Fire Pit on Concrete

Old 03-08-17, 10:33 AM
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Fire Pit on Concrete

So we are having a 12 to 14' concrete circle poured. I have heard that you shouldnt put a fire pit on concrete. The answers seem to vary. So should I just have them pour a circle but leave a 36" fire pit ring kinda like a doughnut? Or can I just throw some sand and grave in the bottom on top of the concrete and be good to go?
Old 03-08-17, 01:15 PM
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What is your fire pit? Is it a metal ring with an open bottom that will sit on the concrete? Is it a metal "wok" that will stand above the concrete on legs? How well do you want to protect the concrete? Do you want the pit to be removed later without visible damage to the concrete below?

The problem is the heat going down into the concrete. Hot enough and it will vaporize the water in the concrete and can cause it to spall or crack, sometimes with a surprising "pop" with bits flying about. So, a lot will depend on how big a fire do you plan and how long will it burn and how the fire is separated from the concrete? A small fire for a short time can be set right on the concrete without harm. The hotter the fire and the longer it burns the more you'll need to protect the concrete.

A couple inches of sand in the bottom of a fire ring can work for your average fire of an hour or so. The problem is it's difficult to clean out the ashes without getting into the sand and if you're not careful after a few fires it's easy to be down to nothing under the fire. Fire brick is a really good way to go. Cover the bottom of your pit with fire brick and sweep sand into the joints in between. It's easy to clean out the ashes and you've always got the brick thickness of protection.
Old 03-08-17, 02:14 PM
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We have a huge 10' dia fire pit in the back yard ringed with bolders that are approx 18" in dia.

Over the years they have all cracked or split due to the heat.

Now granted this thing gets used for massive fires at time, like burning up many large (30" dia) oak trees.

If you want to save the concrete, build a bigger center hole, line a foot of pavers to take the brunt of the heat and just leave a dirt patch in the middle.

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Old 03-08-17, 03:17 PM
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There is a reason it is called a fire "pit".
A fire pit is a somewhat dug out area in the ground which will contain all the residue from a fire.
By putting it on top of the concrete rain will wash the ash and remains across your patio.

If you wanted a ground level fire you should put a ring where you want the fire and do not put concrete into it.
You can then fill it with aggregate and then make some kind of border to ring the fire.
Those circular concrete blocks make a simple ring and you can get mesh attachments for a slightly raised fire.

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