Concrete V's Fire Proof Mortar

[danknapp]

I have designed an oven shape that I want to make myself. I have sourced some fire proof mortar from the company listed below. My problem is that I need quite a lot of mortar and the cost of it alone is over $900. So my question is this.
Can I make the bulk of the oven out of normal concrete and then just cover the oven with the fire proof mortar?
Do I even need fire proof mortar, is there a cheaper alternative.

High Temperature Mortars, Fire Bricks, High Temperature Materials, Castables

[Les]

Re: Concrete V's Fire Proof Mortar

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Can I make the bulk of the oven out of normal concrete and then just cover the oven with the fire proof mortar?

High Temperature Mortars, Fire Bricks, High Temperature Materials, Castables

No, regular concrete cannot withstand the heat. Nice drawing though. You can make the home brew mix, but I have no clue if it would be strong enough for your app.

[Les]

Re: Concrete V's Fire Proof Mortar

Can I make the bulk of the oven out of normal concrete and then just cover the oven with the fire proof mortar?

No, regular concrete cannot withstand the heat. Nice drawing though. You can make the home brew mix, but I have no clue if it would be strong enough for your app.

[dmun]

Re: Concrete V's Fire Proof Mortar

As Les said, portland based cements will just crumble at oven temperatures. Mt. Martha appears to be in Australia according to google, so there is some justification to making your dome out of castable refractory instead of fire brick, which is silly expensive down under. Some Australian builders have used a type of brick called a "pressed red", which is much more affordable.

A couple of design notes: your door ledge (the reveal) should be at the back of the entry, not the front. This will allow you to do retained heat baking, and make your oven much more versatile. Also, your oven will smoke MUCH less on startup, if you have a funnel shaped transition instead of a hole the size of the flue in the entry.

Good luck with your project. Keep us posted.

[Tscarborough]

Re: Concrete V's Fire Proof Mortar

You have it backwards. You can cast a thin shell of refractory concrete, then coat it with normal render/concrete. Any area subject to extreme heat via direct flame exposure has to be refractory. You should also adjust your throat/smoke chamber to encourage a better draw, i.e. the outer opening should be lower than the inner and you should have some volume in the smoke chamber itself.

[asudavew]

Re: Concrete V's Fire Proof Mortar

And watch the ratio of your "door height" to the "apex of the dome."

You want to keep the door height around 63% of the dome height.

Example: Dome height = 22"
22" x 63% = 13.86"

The door opening should be around 14" tall.

[Neil2]

Re: Concrete V's Fire Proof Mortar

"Any area subject to extreme heat via direct flame exposure has to be refractory. "

Any concrete that is going to get hotter than 550 F should be refractory not portland based.

[mgh]

Re: Concrete V's Fire Proof Mortar

Can anyone tell me where I can find refractory cement (not mortar) in northern California

[sacwoodpusher]

Re: Concrete V's Fire Proof Mortar

There IS a concrete that you can use.......Here it is:

FIREROK HIGH TEMPERATURE CONCRETE

This concrete costs about $30/54 lb bag PLUS SHIPPING. Be warned....shipping concrete is EXPENSIVE.

Casting a "rounded" organic shape is also a pain, unless you are going to build many of them. This is why people choose firebrick.

By the way, I tried to use Calcium Aluminate....it takes a better bricklayer than me to use that stuff. I use a mixture of type S and fireclay/mortar clay.

Remember that ovens have been around for centuries, before firebricks and refractory materials. Don't make this harder than it is.