Hearth with sand layer?

[brianplaugher]

I have not yet decided which oven to get, exactly, but have a question about a sand layer underneath. One importer and some home-brew enthusiasts suggest a 4" support slab topped by 3" of sand topped by another 3" of cement topped by the fire bricks of the oven bottom. One disadvantage posted elsewhere on this forum said that if the sand got wet it would take a long time to bake it dry. Other pros and cons? I'm also interested what folks think about at which level in the sandwich it would be appropriate to add ceramic insulation board.
Any guidance appreciated.
Brian

[SableSprings]

Welcome Brian!

Most of us on this forum support the 4" of reinforced concrete hearth. Next you want to put down insulation, which can be perlite or vermiculite mixed with cement (5:1) or insulated ceramic board. Water uptake/retention for both of these products is a downside, so making sure water can drain away or providing a waterproof dam around the insulation perimeter is highly recommended. The best solution (and most expensive) is to put down a 2" layer of foamglas directly on the hearth and add 2" of ceramic board on top of that. (The foamglas does not wick water and so provides a water barrier underneath). Sand is not an insulator and is only used as a thin layer (with some fireclay added) to allow you to level the firebrick cooking floor that's laid on top of the insulation layer.

Perlcrete or vermicrete (the less expensive insulation types) is about half as efficient as the foamglas/ceramic board options, so if you went that route...4" to 6" would be the minimum of the 5:1 mix you'd want to include (and 8" even better ).

You can either place your dome base just outside the cooking floor bricks (in which case the dome base needs to be seated on the insulation) or the dome can be laid down on the outside ring of the cooking floor bricks. You'll see good reasons to do it either way...but if you ever envision replacing outer area cooking bricks, obviously not having them under the dome base is an advantage .

The biggest issues you need to address are properly insulating the cooking floor and keeping moisture/water out of your insulation layers. Topping 3" of sand with 3" of concrete directly beneath the cooking floor just creates a huge mass that will suck most of your heat away from the cooking floor...not what you want in a pizza oven.

Hope that helps...make sure to look at the documented builds highlighted in the following link:

https://community.fornobravo.com/for...n-the-archives

p.s. Here's a link to another important concept for getting/keeping perlcrete or vermicrete base layers to dry (and stay dry).

https://community.fornobravo.com/for...516#post405516

[UtahBeehiver]

Plus one on Mike's comments, right on the button.

[pecker88]

The best solution (and most expensive) is to put down a 2" layer of foamglas directly on the hearth and add 2" of ceramic board on top of that. (The foamglas does not wick water and so provides a water barrier underneath).

Any idea where I could find foamglas in the US? Either in a store or order it? Looks like they pulled it from the US market in 2016, everything I find online is from Europe...

[UtahBeehiver]

You won't find this material at big box stores, call some local insulation or refractory distributors. Try Distribution International or Industrial Insulation. FoamGlas is water proof and has good compressive and thermal values but is sensitive to abrasion. Cuts very easily but is is costly too certainly as much as CaSi board. The key is to keep the CaSi from sitting in water that might find its way onto the hearh. This can be accomplished other ways too, P/V crete layer, one builder place patio blocks on the hearth under the CaSi to raise it off the floor, etc.

[SableSprings]

Any idea where I could find foamglas in the US? Either in a store or order it? Looks like they pulled it from the US market in 2016, everything I find online is from Europe...

Foamglas was originally developed and made by Pittsburgh Corning and although it was pulled from the residential market, the industrial market is still active in the US. The nearest distributor to you that I found is on the east side of St. Louis (link below) and you might either give them a call or e-mail to see if you could get some "samples" that would be enough for your underbase insulation. They might be able to give you information regarding a construction company or commercial supply business in your area that has made a shipment purchase of Foamglas board and that might have some "scraps" that would work for the oven. As Russell noted in the previous post, it may be just easier to fall back on some other options to keep the CaSil board "above water".

GIC St. Louis | GM Ken Jung
1630 Macklind Ave
St. Louis, MO 63110
United States (US)
Phone: 314-771-1200
Secondary phone: 866-550-5565
Fax: 314-771-1201
Email: kjung@generalinsulation.com

Last year, the company was acquired by Owens Corning (along with the Foamglas division). Owens Corning appears to be actively continuing to develop and improve the Foamglas line. You can search on the Owens Corning website for Foamglas and get some additional contact info if you want to continue to pursue this option for the base insulation.

[pecker88]

Thanks everyone! I found a company in Omaha that can get foamglas, you have to order by the case though.
2 inch thick,18x24 inch pieces, 1 case is 36 sq ft and it's $5.37/ sq ft. So, $193.32 plus tax. Oh well, it's nothing in comparison to the $3k Casa 100 kit...

[BrixxGrill]

Welcome Brian!

Most of us on this forum support the 4" of reinforced concrete hearth. Next you want to put down insulation, which can be perlite or vermiculite mixed with cement (5:1) or insulated ceramic board. Water uptake/retention for both of these products is a downside, so making sure water can drain away or providing a waterproof dam around the insulation perimeter is highly recommended. The best solution (and most expensive) is to put down a 2" layer of foamglas directly on the hearth and add 2" of ceramic board on top of that. (The foamglas does not wick water and so provides a water barrier underneath). Sand is not an insulator and is only used as a thin layer (with some fireclay added) to allow you to level the firebrick cooking floor that's laid on top of the insulation layer.

Perlcrete or vermicrete (the less expensive insulation types) is about half as efficient as the foamglas/ceramic board options, so if you went that route...4" to 6" would be the minimum of the 5:1 mix you'd want to include (and 8" even better ).

You can either place your dome base just outside the cooking floor bricks (in which case the dome base needs to be seated on the insulation) or the dome can be laid down on the outside ring of the cooking floor bricks. You'll see good reasons to do it either way...but if you ever envision replacing outer area cooking bricks, obviously not having them under the dome base is an advantage .

The biggest issues you need to address are properly insulating the cooking floor and keeping moisture/water out of your insulation layers. Topping 3" of sand with 3" of concrete directly beneath the cooking floor just creates a huge mass that will suck most of your heat away from the cooking floor...not what you want in a pizza oven.

Hope that helps...make sure to look at the documented builds highlighted in the following link:

https://community.fornobravo.com/for...n-the-archives

p.s. Here's a link to another important concept for getting/keeping perlcrete or vermicrete base layers to dry (and stay dry).

https://community.fornobravo.com/for...516#post405516

Hello Mike,
Thanks for all of the excellent posts! I´m hoping you can guide me in the right direction here. I´ll be putting a modular oven on a metal stand and base, to be used in a comercial food truck. The "base" is a 6" deep steel pan, and the oven's cooking floor is about 2.5" thick. I want sufficient thermal mass to allow us to keep the temperature of the floor hot and not slow down our production during peak times. What would you recommend I use for this "base" or "slab" if you will? I live in the Dominican Republic and some materials are hard to come by, but I can get my hands on perlite, refrectary cement, ceramic board, etc. The sales guy at the company I´m buying the oven from has suggested a mix of portland cement, dry sand, and perlite. But I´m wondering if this will serve more to insulate than to give me more thermal mass. The oven I currently use sits on a concrete slab with ceramic board on it and the oven floor on top of that, but the floor will get cold quickly during peak times, and I can´t risk that happening in this food truck, which will be even busier. Thanks for your reply!

[david s]

Vermicrete or perlcrete can be tailored for strength or insulation. A high proportion of vermiculite or perlite gives you more insulation but lower thermal mass and strength. Conversely more cement and sand will increase thermal mass and strength, but lower insulation value.
This little table should help you achieve what you require. (Thanks for the amendment Russell)

[UtahBeehiver]

You actually need both good insulation and thermal mass in order for you oven to work in a high production mode. Insulation to preserves or minimizes heat transfer from your cooking surface and more thermal mass allows more btu(s) storage. Your highest insulation bang is CaSi or AlSi board 3" to 4" then adding thermal mass, could be done with an additional layer of fire bricks either 2.5" standards or 1.25" splits.Does the oven floor sit in the pan or on top of the pan? Can't have both ways, good insulation and thermal mass in one product. Attached is a table showing pcrete thermal ratings. Notice the addition of sand to the mix dramatically reduces the thermal value of the pcrete. Pcrete is an insulation option but it takes more thickness to equal the same thermal insulation of CaSi/AiSi

[mongota]

I'd recommend 4" of board insulation under the floor. Your current oven floor is made up of 2-1/2" thick bricks. You can repeat that if you think that 2-1/2" thickness will give you enough cooking time with the 4" of insulation underneath.

Or you can stand the floor bricks on edge and get a roughly 4-1/2" thick floor. It'll obviously take longer to charge the thicker floor with heat, but the added mass might help get you through your busy times.

[SableSprings]

BrixGrill, take a look at Karangi Dude's thread/build of his mobile pizza oven. Here's the thread link
https://community.fornobravo.com/for...-s-mobile-oven

There are several other threads started concerning mobile oven builds that are worth looking at in the Commercial Pizza Ovens section of the forum. Also several in the Australian Regional section. It would be well worth your time looking at some of those threads. I don't have any experience with the traveling oven option but there's a lot of good advice and documented builds scattered throughout the forum...I'm pretty sure David S (post #9 above) has also been involved with building a WFO on wheels

I suspect you wouldn't be interested in the mobile pizza option by Forno Bravo, but you should look at their well designed product(s).
https://www.fornobravo.com/product-s...e-pizza-ovens/

Sorry to "Thread Hijack" Brian...

[bentedesco]

Thanks everyone! I found a company in Omaha that can get foamglas, you have to order by the case though.
2 inch thick,18x24 inch pieces, 1 case is 36 sq ft and it's $5.37/ sq ft. So, $193.32 plus tax. Oh well, it's nothing in comparison to the $3k Casa 100 kit...

Another option is just to use concrete pavers/solid cap blocks, the goal is just to get the Fb board off the hearth to keep it away from moisture.

Check out this thread here:
https://community.fornobravo.com/for...-fb-board-ebay