Record of my 32" Homebrew cast oven, on a brick base - West Midlands, UK

[david s]

Suggestions for filling the thermal break? I have a couple of commercial options from vitcas when I put my original order in, or some suggest just Vermicrete.....

It'll be too hot for the high temp silicon in that location. The other stuff will handle it but it sets rock hard and doesn't remain elastic. I've not found any product yet that can remain elastic for the kinds of temperatures they experience in that location, but happy to be proved wrong. I just use a 5:1 vermicret which, being weak has some elasticity to it.

[deejayoh]

Suggestions for filling the thermal break? I have a couple of commercial options from vitcas when I put my original order in, or some suggest just Vermicrete.....

I used Kaowool Caulk. Refractory stuff. https://www.sheffield-pottery.com/Hi...wool-p/tcm.htm
I stuffed in some high-temp rope, and then sealed up with that stuff. It's held up for 8 years now.

[hughjamton]

Hi, Could you tell me how many firebricks you used for your floor, I can't quite work it out from the photo.
Cheers

[Nick J C]

hughjamton , I ordered 35 and only had a couple left over

[sergetania]

It'll be too hot for the high temp silicon in that location. The other stuff will handle it but it sets rock hard and doesn't remain elastic. I've not found any product yet that can remain elastic for the kinds of temperatures they experience in that location, but happy to be proved wrong. I just use a 5:1 vermicret which, being weak has some elasticity to it.

Sorry, what thermal break are you talking about? Is it the gap between the separately cast facade and the gallery? Is it too hot for a 600F high temp silicone? Does it need to be filled at all (besides the outer render)? I can't find any other breaks in that oven being one-piece cast.

Thank you!

[david s]

Sorry, what thermal break are you talking about? Is it the gap between the separately cast facade and the gallery? Is it too hot for a 600F high temp silicone? Does it need to be filled at all (besides the outer render)? I can't find any other breaks in that oven being one-piece cast.

Thank you!

I think I misinterpreted the location. Looking at Nicks pic it looks like he is not talking about a gap between the gallery and dome chamber, but between the gallery and outer decorative arch. In which case the high temp silicon should be ok. I just leave an air gap on the sides and at the top. You really only need to fill the space at floor level.

[sergetania]

Thank you, David, for unconfusing me... at least about this particular issue

[Nick J C]

Constructed a door out of a 2" vermicrete slab cut to shape with a hand saw to a little smaller than the inner arch into the dome, backed by 1/4" cement board to form lip. Stainless handles (old stock) screwed in to the cement board with penny washers to distribute load as it is weak stuff. Hopefully they wont get too hot as screws do not penetrate vermicrete insulation. Temporary glue gunned together to check position , then drew round vermicrete on cement board, and fixed with fire cement (no other use for it - see above). Finished with a few aluminium caps hammered to shape and knocked on to corners.

Have ordered some glass rope to glue to the flange to make a seal.

Not sure how long the cement board will last, but if it disintegrates, good excuse to get my father to weld me up a stainless one

[sergetania]

That looks almost like a vault door! Heavy?

I love how the entrance to the oven looks with the new door. Hopefully it's pizza time soon!

[Nick J C]

The vermicrete is pretty light, although i made it a rich mix for a bit more strength - door wieght 9Lb (4kg). I will replace the aluminium caps with some proper u-channel if the cement board doesnt disintegrate on the first firing!

[Nick J C]

Door painted with stove paint

[Hattori-Hanzo]

Wow! now that's an oven to be proud of. Do you have any more pictures.

[Nick J C]

I am beginning to think about how best to waterproof dome. My options appear to be:

1) make a roof, to prevent water touching the dome
2) Use a commercial cement based waterproof stucco/render
3) Use standard render with a waterproofing additive
4) Use standard render (lime/cement/sand mix) and masonary paint

I think I am most likely to leave the dome exposed - I may put up some sort of more permanent shelter, but would prefer not to have to. I would be interested on views on the above?

I am also thinking about venting the dome, as it is unlikely to be fully weathertight. Options I think are:

1) vent the top of the dome - either with a large bore copper pipe set in the render, penetrating to the blanket - with a rubber cork which is removable, or perhaps a loose fitting cap, or one of the plastic air admittance type caps that you can get from auto stores. I would probably go for the former, with a homemade metal mushroom cap.
2) vent the flue - using david s design of earthenware disks around where the flue emerges from the render - I may do this in stainless rather than clay as I dont have access to a kiln easily, or I may go for option 1. Can I clarify David, how you seal the top clay disk onto the flue - sealant? If temps here are high, how would this work? Why does the disk not crack if sealed with rigid fully heat resistant cement?

[david s]

I think the best solution is to have a roof over your oven, or an enclosure. If rendering an igloo if you make it waterproof then it can’t breathe and will trap moisture beneath it making drying the insulation space more difficult. Most commercial renders have some waterproofing added making them partially breathable and partly water repellant.
Regarding my system the lower clay flange has a larger diameter than the flue pipe so moisture can pass between it and the flue pipe. The upper cap is sealed to the pipe with high temperature sealant. The gap is 5mm. If less the expanding pipe could crack the clay. If wider too hard to fill. Because it is quite high due to the generous funnelling of the flue gallery, it’s not too close to the fire. Although my wife fired the oven up one day and had flames going up the pipe which cooked the high temp silicon. Under sensible operation (me) the seal is perfectly adequate.

[sergetania]

Nick, have you considered tiles for the outer shell? Is it possible to waterproof tiles? It could look pretty.