55 gallon drum pizza oven

[tylerbecker]

Hello all,
I'm planning to build a pizza oven inside of a 55 gallon drum. I plan to pour a 1” layer of perlite/cement insulation layer on the inside of the drum, then follow up with 2” of homebrew castable. My question is, will the castable adhere readily to the insulation layer even though it will be a cold seam?

[david s]

I think this is a great idea. It will make the build really fast and easy. One inch of perlcrete is minimal though, so you should make it as lean as possible, say 12:1. Drying that layer before laying up the castable against it will be imperative because the steel outer skin will act as a moisture barrier. Don’t worry about the castable bond with the perlcrete, it wouldn’t matter if there was no bond anyway. Eliminating the water from the perlcrete is far more important.
I cast some 5:1 perlcrete using calcium aluminate cement, inside a 9kg gas bottle for a small forge a few years ago, the idea being it would act as a hot face as well as being an insulator. I left it in the sun for a couple of weeks, but we had trouble firing it using a gas burner. I couldn’t conclude if it was the chamber design or damp perlcrete. I advised the customer to let it dry in the sun for a few more weeks and try again. Haven’t heard back.

[tylerbecker]

Thanks David, for the quick response and advice! I'm anxious to get started! Would you still reccommend used the burnout fibres and SS needles in the refractory cast?

[david s]

Definitely add the burnout fibres. The stainless needles are hard to obtain, especially in small quantities, expensive and make placement difficult, so maybe skip them. When adding the burnout fibres, don't add them to the dry mix because they ball up like a fur ball. Ad them to the wet mix and pull them apart adding slowly as you mix. Doing it by hand is better so you can inspect for adequate dispersal.This takes longer than you'd think.

[tylerbecker]

At what ratio should I add the burnout fibers?

[david s]

1% by volume. It’s less than you’d think but mix them in more than you’d think.

[tylerbecker]

Thanks again!