Poor mans Refactoring cement as Castible.

[wemme]

Hello all,
Over the year or so i have read many books and manuals on pizza ovens and put the following question for debate. (i expect a good heated one )

Can we use the poor mans Refactoring cement as a castible???

• All the early clay ovens of history used about 3 parts sand to one part clay and have staisfactory heat holding ability... similar to the poor mans mix so will have the heat holding ability

• Granted that this recipe will not handle direct flame contact well it is still recommended to have a fire brick floor and perhaps a ring or two of fire bricks for the first part of the dome.

• In New Zealand the fire bricks are in the order of about $5-$6 NZD each which can make an oven too expensive to build. where as the poor mans refactoring cement costs are fairly low and easily availible. also suppliers here hardly ever seem to have any knowledge of their firebricks and try to sell you any old rubbish.

• A simple geodesic dome mould could be made and tiles poured then cemented together or simply slapped and slopped over a news paper coverd sand mould.

• the main reason i would not use a clay oven is the fact that the oven needs to breath (i.e. un sealed) or otherwise the condensation builds up and the oven collapses also the mix is very soft. also as you can't seal it you would need to build a roof over the oven to protect it from the weather.

• My hope is that the poor mans mix will be the best of both worlds. Cheap easy but practical.

What ya recon???

[nissanneill]

I for one would not use it.
Even though I used poor man's mortar, I would not use it for a castable.
Rather, I would build an oven using solid fired clay paving bricks and poor man's mortar, a simple replacement for the expensive firebricks. They are just as expensive over here also.

Cheers.

Neill

[wemme]

okay fair enough but any technical reason why you wouldn't use it. have you had any spalling or deteriation of your mix?
Regards
Bart

[dmun]

okay fair enough but any technical reason why you wouldn't use it.

Yes, the size of the aggregate in any concrete should correspond to the thickness of the project. You could in theory obtain refractory chunks like broken firebrick to do this, but it isn't a commercially available material.

[Nic The Landscaper]

Refractory Mortars shrink considerably in comparison to regular mortars and concrete. It is just the nature of the clay. That is why joints need to be tucked and pressed as the mortar hardens or you end up with significant cracking in your mortar joints, which is a common occurrence here at FB, and really isn't a major issue other than aesthetics.

But in the case of casting an oven with a clay based refractory mortar, the degree of shrinkage will likely cause catastrophic cracking and a failed oven. To my understanding (I haven't spent much time looking into this direction as I love the look of brick) castable refractories use a high aggregate content to reduce the impact of clay shrinkage, and some utilize synthetic bonding agents to help hold everything together.

My recommendation would be to look into purchasing a true castable refractory mix, or try to find a better recipe for a castable refractory than the Refractory mortar mix we use.

[eprante]

I am with Neill on this. Many builders have used regular clay pavers to build their ovens with little or no problem with spalling of the bricks. Build a brick oven.
Eric

[david s]

I don't think a lime and clay based castable will be strong or durable enough. If you're trying to do it on the cheap why not try the poor mans mortar and rocks over a sand hump. Proprietary castables contain clay, but in the fired and crushed state which eliminates the shrinkage problem of unfired clay. In addition the cement used is calcium aluminate which is much stronger than the lime used in the poor mans mortar.

[nissanneill]

Wemme,
Portland cement doesn't react to excessive heat produced in an oven very well and rapidly breaks down.
As recommended, buy the proper refractory castable if you are determined to go down that path, firebricks (if reasonable and available) fired clay pavers as a third option and last common fired red house bricks.
At least you will have a satisfactory brick Pompeii oven to use that is reliable and reasonably priced.

Neill

[lwood]

I used fired red clay brick and it works fine. It probably doesn't hold the heat as long as other ovens, from some of the others comments about how long their ovens retain the heat. But it works fine. Coming up with a castible formula that works seems a little too risky.