Perlite for enclosure

[Rbhumbert]

I am building the 42" dome oven as per FB plans. I want to have an enclosure that is arched at the top and straight sides. I am considering forming the shape of the enclosure, adding some pencil rod for strength, and filling it with a perlite/concrete mix. After stripping the forms, I plan to finish out the enclosure with Faux brick. The dome would be covered with a minimum of 4" of perlite/concrete mix, but in areas it would be 6-8" thick. Can you have too much perlite/concrete insulation? Could it expand too much when heated and cause problems with the Faux brick finish? Any thoughts, ideas for warnings would be appreciated.
Rbhumbert

[thickstrings]

Re: Perlite for enclosure

I don't think you can have to much insulation, but you will be getting some diminishing returns for your efforts. On my build I have a 39" dome with 3-4" of cf insulation, brick walls, and a "hip" roof. I started putting a vermi-crete mixture over the insulation in 1-2" lifts and each lift kept getting stronger with portland and continuing to shape the "hip". When it got where I wanted, about 10," I poured a all concrete top over it in the "hip" shape,overlapping the sidewalls and forming a soffit. I might suggest that if you are going to add "fake" bricks to the sides, why dont you use a cement board to build your walls with..might be easier, you can still go over the top with whatever shape you want,and use the cement board as a guide for your roof. Heres a in the process picture before I put the final concrete top on it. All that vermi-crete takes a while to dry and might be hard to stick fake bricks to. I need more pic's but, wife has camera and is visiting family.... as a after thought, all I am saying is use the cement board for your forms, and then leave it up and put your bricks on it....with some interior framing of course....

[Rbhumbert]

Re: Perlite for enclosure

Thank you for your thoughts. Your picture shows almost exactly what I have in mind, but I was considering Faux brick because of the wider selection of colors. My wife has this thing about red brick and the other colors available in real brick. Maybe I can find a real brick she likes , set the enclosure, then fill with perlite/cement mix.
Rbhumbert

[thickstrings]

Re: Perlite for enclosure

As a side note, I filled the wall sides with dry vermiculite.....the mixed stuff is only on the top....The more portland that you use , the less insulative it will be....the dome is also sitting on 2" of cf board...no need for forms if you build a brick wall around it all....just leave room for the insulation...I would suggest using the cf blanket and board though...and then, the vermiculite,perlite.....