Help with expanding/contracting concrete in firepit!

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Old 07-20-15, 11:05 PM
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Help with expanding/contracting concrete in firepit!

I built a firepit about a year ago, a 4" concrete ring roughly 2' diameter lined inside with firebrick, top with pool coping, outside with tile. Every time I fire it up I get a crack that splits as it heats up, then comes (mostly) back together as it cools. This cracks the mortar/concrete/grout and looks crappy! Any suggestions how to prevent this?? Am I just SOL?
 
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Old 07-21-15, 05:02 AM
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Do you remember what mix you used? Was it poured all at the same time? Can you post a pic?
 
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Old 07-21-15, 05:10 AM
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Old 07-21-15, 06:48 PM
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Some pics to help explain

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Here are some pics, the first of the finished project, which I was proud of...
I used regular cement from home depot, I don't remember if it was high strength or regular. I made a form out of masonite and did it in a single pour, no rebar! my bad... the next 2 pics are from inside the pit and from top after i removed a few top bricks. Crack opens when pit is hot and contracts, a little, when cool. I was thinking of firing it up, waiting until it expands, then pouring fine sand into the crack to keep it open, then re-mortaring/grouting. Am i asking for trouble??
 
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Old 07-21-15, 08:15 PM
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The title of your post said concrete & the last post said cement. That could be the problem. Before you try to fix it, see if you can find the heat limit, on the products that you may have used or plan to use.

BTW, I like the design. It looks really nice.
 
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Old 07-21-15, 09:53 PM
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concrete! not cement

sorry! yes i used a concrete mix from home depo. It was sakrete but I don't remember if it was the high strength or the regular mix... Wish I did, live and learn! I lined the inside and bottom with yellow firebrick. I then used regular mortar, which from reading I've learned was not a good idea, to mortar in the firebrick on the sides and on top. I thought the firebrick would prevent the conduction of heat to the concrete but perhaps the mortar is conducting. Any ideas on a fix to my self made mess? If needed I could chisel out the mortar and re-mortar with high strength mortar. Would this reduce the conduction of heat? I couldn't find the heat limit of any sakrete products, the data sheets don't address this... Thanks for any ideas and for the compliment! I built it right behind my pool with the same coping on top and tile, looks nice together!
 
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Old 07-22-15, 03:37 AM
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I'm not sure that the mix is the problem. It could have been the lack of rebar.
Quikrete has a tech data phone # at:

QUIKRETEŽ - Technical Data

It might be worth a call.
 
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Old 07-23-15, 03:01 PM
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you forgot your hi skoul fiziks - heat causes solids to expand & cold causes liquids to expand,,, imo, the only way you can negate this issue is by never building a fire in it again,,, that being said, you can always place a pit inside the pit but, this time, use intumescent materials that'll withstand the fire's temps
 
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Old 07-26-15, 07:17 PM
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I'm jealous. None of the fire pits I've built looked as pretty as yours!

But none of them cracked, either. Maybe it's because I make a practice of leaving an air gap between the concrete outer ring and interior fire brick/steel liner ring. Giving heat a chance to escape before being absorbed by concrete (not having expansion joints in it) is a practical solution to prevent thermal expansion cracking.
 
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Old 08-01-15, 02:04 PM
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that bdgeman's pretty smart
 
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Old 08-01-15, 07:03 PM
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Not really that smart (just ask my ex-wives!). But I haven't forgotten everything I've learned over the last 50+ years of my adult life, either.
 
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Old 08-02-15, 08:10 AM
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That is what fire rings are for!
 
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