Heat retention with a cast refractory oven

[fastball]

I'm new here and see many people that have built their oven with castable refractory, at around 2" thick. I'm wondering what the heat retention is like? Is this only good as a pizza oven, or can you retain heat enough to bake bread, roasts, etc?

2" seems to be a little thin, but I understand that there is no problem handling the heat, it's just the retention once you sweep out the fire that I'm inquiring about.

Also, has anyone given any thought to a 4" castable refractory oven? Seems it would have the mass, but maybe that's just too much weight.

Has there been any problems with thermal cycling with your castable ovens?

Yes...I have many questions. Sorry, still researching, trying to decide a direction.

Thanks.

[MarkG]

Re: Heat retention with a cast refractory oven

I too am thinking about using castable. I will aim for 3 or 3.5 inches I think. How have others used the castable? Are molds needed? Is the castable thick enough that it can stand up against a sand form and not excessivly slump? I'd like to cut the archs (inner and outer) out of plywood and put a piece or dowel/rebar etc and use it as a axis to rotate the plywood around to define the shape (one for the inner sand and one for the outer dome surface then just pull the dowle and fill with castable).

If its not too vertical it might work. Could use firebrick as a soilder course for the base (vertical or near vertical rise) if the castable would overly slump. Otherwise think I will construct a hexagonal mold. Any thoughts?

thanks,

Mark

[david s]

Re: Heat retention with a cast refractory oven

If you make a wooden mould for the entry, cover it in plastic and use wooden wedges under it to facilitate removal.If you get the consistency correct the material will stand up on its own. People tend to make the mix too wet to make it more fluid. Better to stick to the recommended water content to attain full strength and use vibration to eliminate voids. It goes off pretty fast and is expensive so make small quantities 50lbs at a time. You can add stainless steel needles for reinforcing.

[dmun]

Re: Heat retention with a cast refractory oven

I too am thinking about using castable. Any thoughts?

Why? Most of the castable refractory ovens are made in places where firebrick is ruinously expensive. In the US, the superior material is less expensive than the hard-to-use-and-ugly-as-homemade-sin bagged stuff.

[MarkG]

Re: Heat retention with a cast refractory oven

Dmun,
You got me thinking. Looking at your threads and combining some of the concepts you had with mine, I think I might have an idea that might work. I am thinking I could pre-fab components as you did and assemble them but with less required skill.

I am thinking of doing a hexagonal structure (truncated hexayurt). I could just stack and morter streight "wall" sections and then simply cut my parts with a streightedge and a circular saw with a diamond blade and assemble. the top center piece would concern me being composed of bricks so I could just cast the one piece in place and it wouldn't be very visible.

Did you run into any issues with the long running seams cracking in the end?

Mark