# Best insulating sand for concrete blocks



## scvinegarpepper (Dec 7, 2021)

I've got a cinder block barbecue pit that I cook whole hogs on, probably just once a year. But each year I seem to keep making modifications to it to improve cooking on it. The blocks are currently stacked (staggered) but are not mortared/permanent. This year, I want to fill all the empty cells in the blocks with sand for better insulation on the pit. My question is what type of sand would be the best insulator? From my local supplier, my choices are: sand-clay mix, play sand, and mason sand. Thoughts?


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## chopsaw (Dec 7, 2021)

They use a Vermiculite block fill in exterior block walls that won't get furred out on the inside . 
You don't want something that will pack tight or hold moisture . 
Vermiculite is a loose fill material that will protect against temp , and moisture .


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## scvinegarpepper (Dec 7, 2021)

chopsaw said:


> They use a Vermiculite block fill in exterior block walls that won't get furred out on the inside .
> You don't want something that will pack tight or hold moisture .
> Vermiculite is a loose fill material that will protect against temp , and moisture .


Good point. I considered something like vermiculite, but I'm worried it'll get cost prohibitive. There's approximately 40-50 cinder blocks making up the pit. Not sure how much vermiculite it would take to fill those up.


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## JC in GB (Dec 7, 2021)

*You can use perlite to mix your concrete with as well.  That will make lightweight, insulated concrete.*

*I have used perlite **concrete** in my wood fired stone oven project.*
*
Perlite is far less expensive than vermiculite.  At least by me it is....
*
*JC   *


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## scvinegarpepper (Dec 7, 2021)

JC in GB said:


> *You can use perlite to mix your concrete with as well.  That will make lightweight, insulated concrete.*
> 
> *I have used perlite **concrete** in my wood fired stone oven project.*
> 
> ...


What about straight perlite, i.e., without concrete? I'm trying to avoid using concrete or anything permanent. Does perlite absorb moisture?


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## smokerjim (Dec 7, 2021)

How about some small gravel, just a thought.


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## Lonzinomaker (Dec 7, 2021)

Make sure the vermiculite is asbestos free.


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## Smoke-Chem BBQ (Dec 7, 2021)

Air, if it isn't circulating, isn't a bad insulator all by itself.   I wonder how much you'd gain by filling in the dead space in the cinder blocks?  Especially for once a year use.   You'd probably see improvement in heat retention/temperature buffering, but on a pit that big I've no idea how significant it would be.  Just laying cap blocks around the top would keep warm air from the dead space in the lower blocks from rising and escaping.

How hot do the outsides of the blocks opposite the airspace feel when you are doing a cook?


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## ravenclan (Dec 7, 2021)

The big cinder block pits I have seen, Some used sand some did not. I asked one of the pit guys if the sand was used to keep heat. He said, He used it to retain heat and also to keep it more stable. But he also said to "preheat" the pit to get any moisture out but he also said that will happen anyways when you do your burn to make the fire.
The other that did not use sand said he didn't see a difference in heat. and he tore down his smoker to rotate the cinder blocks. The reason he did that was to make sure the cinder blocks did not burn up or become brittle due to the heat.


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## JC in GB (Dec 7, 2021)

scvinegarpepper said:


> What about straight perlite, i.e., without concrete? I'm trying to avoid using concrete or anything permanent. Does perlite absorb moisture?



Perlite absorbs and holds moisture.  So does vermiculite.  You can use straight perlite if you don't need it for structure.  I use loose perlite in my oven walls.


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## scvinegarpepper (Dec 7, 2021)

Smoke-Chem BBQ said:


> Air, if it isn't circulating, isn't a bad insulator all by itself.   I wonder how much you'd gain by filling in the dead space in the cinder blocks?  Especially for once a year use.   You'd probably see improvement in heat retention/temperature buffering, but on a pit that big I've no idea how significant it would be.  Just laying cap blocks around the top would keep warm air from the dead space in the lower blocks from rising and escaping.
> 
> How hot do the outsides of the blocks opposite the airspace feel when you are doing a cook?


They get slightly warm, but nothing crazy. You can hold your hand on them and not get burned.


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## chopsaw (Dec 7, 2021)

scvinegarpepper said:


> . I considered something like vermiculite, but I'm worried it'll get cost prohibitive.


I was thinking this was something you had built and stayed in place . If it's being set up and taken down , no reason you couldn't use sand if you want to fill it with something .


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## Brokenhandle (Dec 7, 2021)

I misread the title at first...made me stop and think why you wanted insulting sand! Insulting... insulating... it's close to the same thing right? 

Ryan


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## Fueling Around (Dec 7, 2021)

scvinegarpepper said:


> I've got a cinder block barbecue pit that I cook whole hogs on, probably just once a year. But each year I seem to keep making modifications to it to improve cooking on it. The blocks are currently stacked (staggered) but are not mortared/permanent. This year, I want to fill all the empty cells in the blocks with sand for better insulation on the pit. My question is what type of sand would be the best insulator? From my local supplier, my choices are: sand-clay mix, play sand, and mason sand. Thoughts?


 I don't see getting much differing insulating from various sand mixtures (as long as it is dry).  Heat sink is the end result of a sand fill in the core.
I would use the cheapest available and /or as 
S
 Smoke-Chem BBQ
 suggested to cap the top to keep out the elements (rain).
A hog pit will not be as fussy as an enclosed smoker.

Friend's family smokes a lot of meat.  The big smoker is a solid log building.  It takes over 24 hours to get the smoker up to a stabilized temperature


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## mike243 (Dec 8, 2021)

Block are porous so it will always take moisture unless coated,plain old sand would be the cheapest route and keep it covered when not in use.


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## unclebubbas bbq (Dec 8, 2021)

You can caulk the joints from the outside...option 2 wrap the outside of the pit in rigid foam insulation, option 3 duct tape the joints with gorilla tape, option 4 use great stuff insulating foam on the exterior joints, opt 5 use shrink wrap on the outside of the pit


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## SmokinEdge (Dec 8, 2021)

scvinegarpepper said:


> I've got a cinder block barbecue pit that I cook whole hogs on, probably just once a year. But each year I seem to keep making modifications to it to improve cooking on it. The blocks are currently stacked (staggered) but are not mortared/permanent. This year, I want to fill all the empty cells in the blocks with sand for better insulation on the pit. My question is what type of sand would be the best insulator? From my local supplier, my choices are: sand-clay mix, play sand, and mason sand. Thoughts?


I played with a cinder block pit for a while some time ago before I gave up and built a wooden smoke house. Like you, I never set the blocks in mortar because I was making changes in design with real world experience cooking in it. I too thought of filling the block with sand but didn’t because I believed this would create a heat sink. 
One of the biggest issues I dealt with was swinging pit temps caused by the slightest of breeze. The dry stacked block leak terrible, so I was thinking of ways to stop this but still be able to change things in the design. My best idea was to skim coat the inside of the walls with grout or refractory cement. This would seal the structure but still allow me to change things if needed. I never did it though. That was about the time I scrapped the idea and went a different direction.


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