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

[Mullster]

Nick J C am I right in thinking you are going to drill/carve through the render layer then to embed the pipe? Did you consider placing it and then rendering around/up to it? I’d sort of assumed I would do the second way but not sure of pros/cons.

[Nick J C]

Mullster ..... the copper pipe went in when I put the vermicrete layer on, and sits up against the ceramic blanket. It could be imbedded at any point I guess though, and siliconed in. I included the pipe description again so it in all in one post.

[sergetania]

Nice job, looks just like one of mine.

How thick is a typical separately cast front arch(facade)? Thanks!

[Nick J C]

Mine is about 60mm thick

[sergetania]

Nick, thank you. Does it also need to be a couple of inches larger than the cast gallery entrance to cover the gap filled with insulation and make up for the thickness of the outer render?

[Nick J C]

Yes, as shown in photos

[sergetania]

Thanks again, Nick and sorry about many questions... Inquiring minds want to know but can't think of more than one thing before asking.

That doesn't need to be cast of refractory concrete, does it? Also, is there a link to the material you used to embed into the facade? I am mostly curious about the shape of the particles. Do they have a flat side or you had to grind the surface to where embedded particles become visible? I think it looks very cool, trying to decide between using pieces of blue ceramic tile or blue glass like they use on the bottom of aquariums.

[Nick J C]

Hi, I used standard concrete, and cast it with two mixes (but Both at the same time), first mix without needles, second with ss needles, to reinforce structure but without the needles being in the surface layer. I also used some rebar, but that may have been unnecessary, and the guru DavidS has prev had cracking with large diameter rebar. I wouldn’t use what I bought, as it was decorative glass but annoyingly the colour was only on the surface. I would go for something rough (tumbled), as it is less likely to break away from the concrete when you polish it

[sergetania]

Thanks,Nick. I may try mosaic tile for the surface then. They say rebar thicker than 3/16" will crack concrete thinner than 2". I may use some though thinking about it, the facade is not subjected to much stress, no bending.

[david s]

There are many ways to skin a cat, but for what it's worth, this is the way I do it. I cast the decorative arch in two layers, each 35mm thick. The inner layer with a mix that contains a high proportion of perlite aggregate, and the outer layer a high proportion of standard 7mm basalt aggregate. My reasoning is that an insulating layer on the fire side reduces conductivity while the outer layer provides for more strength. For reinforcing I use a single 6mm steel bar with also plenty of random mixed AR (alkaline resistant) fibreglass fibres. As the pic shows when I set the arch in place the only thing holding it in place is the mortar at the base, so I run a wire around the flue gallery and use a cable tie to hold it in place against some cardboard which maintains a small gap to allow for expansion. When the final render/stucco is applied it ties in the arch (see embedded thin wire ties) to the outer shell which allows the inner parts of the oven to expand and contract independently of the outer shell and arch.
Some folk don't agree that this is necessary, but I've seen enough bad oven cracks to convince me that it's worth doing.

[sergetania]

There are many ways to skin a cat

Bastards have nine lives!

Thank you for the explanation! It helps! David, what I am really struggling to understand is how insulation blanket applied around the gallery/base of the chimney. Clearly, you don;t have much space for insulation on the back and front of the chimney. I am trying to make the gallery longer because I worry about lack of room for insulation between dome, front and end of the chimney base and facade. Do I need to lay insulation blanket in those areas or not? The heat is coming out of the chimney so it is not like insulation is essential there to keep the heat in. But maybe it is needed to prevent cracking or something like that? Please explain! Thanks

[david s]

The best way I can explain how I do it is with a pic.

[sergetania]

That facade is pretty! I can't see insulation blanket in front above the decorative arch so I am assuming it is not there.

[david s]

Correct. No blanket there. That part doesn’t get too hot. Probably less than an inch of 10:1 vermicrete there.

[sergetania]

Mystery is solved! That's been troubling me. So basically I will pack the blanket on the dome but in tight spaces around the chimney it's not essential.

Thanks! Btw, David, did my casting exercise look on in another thread (Casting practice...) or should I change something?