Refractory Casting Oven

[mendozer]

I've seen the plans for Pompeii ovens, barrel ovens, heck I've even seen the pre-made castings and the foam forms you can buy from diybbq.com or woodlanddirect.com.

I like the smooth look of refractory as well as the rapid heating and the presumably easier task of pouring "concrete" if you will vs laying and cutting bricks.

I'm curious of a few things:

1) have you made a cast oven and did you have a favorable outcome? I know manufacturers usually have joints in their castings to allow for expansion to minimize cracking
2) does cracking even matter all that much?
3) did you buy refractory or make your own? I have a local supplier who carries Kastolite 30 for $55 for a 55 lb bag.
4) how heavy was this oven? I'm thinking of making it on a frame with casters.

[UtahBeehiver]

David S is our casting expert. He can answer your questions. From the past, I believe he said Kastolite was an insulating refractory not suitable for the dome but you need to confirm with him. Most of this questions are addressed in the forum. Do a search on cast ovens and have at it.

[deejayoh]

I've seen the plans for Pompeii ovens, barrel ovens, heck I've even seen the pre-made castings and the foam forms you can buy from diybbq.com or woodlanddirect.com.

Stay far, far away from this one. Bad design

https://diybbq.com/do-it-yourself-co...kit-package-1/

[mendozer]

yeah those were for example of forms. There's no good form that I can find other than a foam 3d one that was much more like $2k. I'd much rather build one. A friend of mine used a physioball for his form. I like this concept, but also I don't know how thick I'd be able to make it. I've seen 2" walls are ideal for cast refractory. Then there's always the wooden frame with sand mound in the middle, but I don't know how exact or smooth I could make it. Then I saw this cool one, with interlocking panels mortared in. This would be good for expansion right?

http://www.theclayhearth.com/finishe...d-final-paint/

[mendozer]

also, for cast, I've seen 5:1 pumice to Portland cement (with substitutes of perlite or vermiculite for the pumice) but those seem more insulative just by thinking of the composition, not conductive. So then I thought of laying the outer layer with the wool cloth stuff and mesh followed by stucco. I'd also use firebrick for the hearth for thermal mass (or other stone like soapstone). I don't have tile cutting tools so bricks would be easier. I'll likely make it on a welded frame with big casters to make it mobile. Assuming this thing doesn't weight like 1000 lbs

[david s]

http://www.pizzamaking.com/forum/Themes/pizzamaking/images/icons/modify_inline.gif[/IMG]

There are many alternatives, cheapest being cob ( mud, sand and straw.). The next is home brew (3:1:1:1 sand,cement,clay, lime). Next is a proprietary dense castable refractory. Kastolite as Russell pointed out is an insulating castable which is not suitable, although if your supplier has that then they probably also have dense castable.
The simplest way is to apply the mix over a sand form covered with wet newspaper. Making it in one piece will result in some fine cracks, but they don't matter, making separate segments for a one off mould is not really worth all the extra trouble.
I build 21" ovens that weigh 250 kg. There is plenty on this forum re cast ovens, so do lots of reading first.

[mendozer]

what's a good pre-mixed castable that's dense enough? If I can source it locally for not much more I'll choose that. And for that formula I'm assuming you mean Portland cement. And what's your opinion on using firebrick grog or pumice instead of sand?

[mendozer]

Also saw this formula on traditionaloven

Mixture: (parts ratio is 3 x 2 x 2 x 0.5, plus water)
3 shovels of the gravel or grog/crushed firebricks
2 shovels of sand (Portland concrete type only)
2 shovels of the cement
1/2 shovel of lime (for Portland concrete type)
This amount will require approximately 6-7 liters of water to mix the concrete.

[david s]

Also saw this formula on traditionaloven

Mixture: (parts ratio is 3 x 2 x 2 x 0.5, plus water)
3 shovels of the gravel or grog/crushed firebricks
2 shovels of sand (Portland concrete type only)
2 shovels of the cement
1/2 shovel of lime (for Portland concrete type)
This amount will require approximately 6-7 liters of water to mix the concrete.

Yes that works too, but I prefer the 3:1:1:1 because it contains a higher proportion of lime which, when/if the Portland cement fails the lime is the cementious material providing the strength. Also the addition of clay in the mix gives it better workability.

[mendozer]

ah ok. Does clay type matter? The pottery supply has numerous types. I also learned that they carry Mizzou. That is a higher density mix of 141lb/ft^3 vs Kastolite's 90. So I also see that people put perlcrete as a base. I would also want a refractory layer above that right? That way the dome and the hearth conduct heat for cooking.

[mendozer]

OK I get it. People are doing different mixes for different things. Insulating layers of either blanket or 13:1:1 vermiculite or perliteortland cement, then the refractory mix of 3:1:1:1 for the dome, then the floor, then the insulating layer of perlcrte of 5:1 vermiculite or perliteortland cement, over a metal mesh.

I was thinking there was one mix for it all

[david s]

The underfloor insulation needs to be a bit stronger. About 5:1 is good, but you need 4" thick, or 2" thick of calcium silicate board (more expensive). Don't use ceramic fibre blanket under the floor, it will compress.
10:1 vermicrete over the dome or blanket (more expensive). I find 13:1 a bit too lean to apply easily.
Clay type doesn't matter, but powdered is easiest to mix with other ingredients. Cheapest is probably bricklayers clay (called fire clay in US) obtain from builders supplies. If getting clay from pottery supplies the cheapest is probably ball clay.

[mendozer]

why the calcium silicate board? I thought the standard was some form of bottom (usually 4" concrete but I may use sheet metal on my metal frame) then the vermicrete as the insulating layer.

[david s]

Yes, you need some sort of support, usually concrete, or your steel stand, but you need insulation between it and the oven floor bricks. Because of the weight over it this insulation needs to be strong enough to support the weight of the dome and floor. If using vermicrete to do the job then it needs to be a 5:1 mix, any leaner is not strong enough IMO, so you need 4" of it because the higher cement proportion reduces its insulating capacity. Alternatively if using calcium silicate board 2" is sufficient. You don't need to use both. Get some prices and you'll see that vermicrete is cheaper, but you have to cast the slab yourself and dry it out so there's more labour involved.

[mendozer]

OK I get you. I thought you were saying I needed both. Yeah I'm gonna do vermicrete for price. I emailed a place in Portland and he said customers have used KS4 and Mizzou with good results for ovens.. At $55 a bag for Mizzou, I'm going to see what the homebrew cost would be. Is there a reference for the quantity needed for this cement mix? I'm having a hard time finding a calculator for volume for this.

Let's hypothesize that I want a 30" inside diameter dome (that's the size of the large physioball I have), walls 2" thick. Not sure if the front opening frame needs to be 2" thick too. What volume of cement would that equal?

Also, I've seen nice forms but using a ball would be so much easier. Except for the fact that I might have to do two layers since putting 2" thick wall is hard on a ball.