Why no refractory cement outdoors?

[dskup]

Greetings from Minnesota!

I'm working on a design to rebuild a simple backyard maple syrup arch, which presently consists of concrete block. It's basically three short walls, about 3' long and 2' tall, forming a "U" shape. The large stainless pan sits on top, the wood goes in the front, a length of black pipe on the rear serves as the chimney. It has worked great for four or five years. But the high heat has caused the concrete to crack and crumble away.

I want to keep things very simple. I could of course buy or make a larger steel evaporator, but for me that would take some of the rustic fun out of it.

So I'm thinking about rebuilding the same exact thing, but lining it with fire brick. My thinking is that the exterior concrete block won't get quite so hot and should withstand the process. The problem I'm encountering is that Rutland's fire brick setting compounds (both mortar and refractory cement) say they are for indoor use only.

Anyone know why? Any ideas how I can get around this?

 

[Valhalla]

Hello Minnesota!

I believe that refractory cement because of its formula has a marginal, even no barrier for moisture penetration and therefore the damage from repeated freeze thaw cycles. Possibly water erosion too.

I would suggest speaking to the nice folks at Rutland directly.

 

[burr]

There is nothing wrong or incorrect with using no mortar in refractory brickwork, actually 'dry lay' is required (in most cases) in the industry. It allows for movement during heat-up, then cooling.

 

[Valhalla]

There is nothing wrong or incorrect with using no mortar in refractory brickwork, actually 'dry lay' is required (in most cases) in the industry. It allows for movement during heat-up, then cooling.

Excellent point! No mortar to fail.

 

[dskup]

Thanks for the replies! But then how would I secure the firebrick to the sides of the "kiln" if no mortar or cement is used?

 

[burr]

Thanks for the replies! But then how would I secure the firebrick to the sides of the "kiln" if no mortar or cement is used?

gravity

edit: also, tie-in anchors, simple SS pins that ties brickwork to shell, sorta like conventional facebrick.

 

[Corey]

Also keep in mind, there is 'outdoors', then there is 'OUTDOORS'. Meaning - you can have your firebox outside, but if you keep it covered, keep the water off the firebrick (which I would recommend anyway) - it's not really 'exposed' to the elements.

 

[dskup]

Yes, it does already wick moisture from the ground. In the Spring, around the time I'm ready to start cooking sap the block is saturated. It takes several hours of burning just to get the block hot enough to expel the moisture. Ideally I would have a system that
a) has the density to retain heat (i.e. the concrete)
b) a liner capable of insulating some of the heat from the block and
c) a way of preventing the system from wicking moisture from the ground.

Of course I could use some kind of water tight insulator as a base, but it would have to withstand a lot of heat.

Maybe this is why commerical makers use steel evaporators. But I'd really like to avoid that if I can.

 

[branchburner]

You might try to contact someone who does masonry heaters, specifically the outdoor bake-ovens.

 

[dvellone]

Thanks for the replies! But then how would I secure the firebrick to the sides of the "kiln" if no mortar or cement is used?

It isn't a good idea to mortar the firebricks to the block even with refractory clay. That joint would likely fail due to the differences in expansion rates of the firebrick and the block.

 

[berlin]

dry lay with firebrick. no need to mortar, if it's clean, level and plumb, it won't move.