The Fresh Loaf

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Insulation Question for Italian Castable Cement Form Oven

moonrattles's picture

Insulation Question for Italian Castable Cement Form Oven

We purchased a four part refractory cement form bread/pizza oven (36" approximately on outside, 32" inside floor diameter) recently to finally put in an outdoor oven. The man had bought it in Italy when stationed there - had same one installed in the villa they rented - they had planned on installing it here when they returned and never did and now moving to a condo. I have the handwritten paper sketch from the place where he bought it - in Italian - suggesting platform height, how to insulate etc :) very very rough. 

I have Kiko Denzer's book and have read it several times as well as numerous sources on the web - we seem to be between methods / approaches - not adobe oven/one piece, but not brick and not perhaps the more "modern" full casted piece kits from the US dealers. 

We have laid a concrete pad and are ready to begin a platform, insulation bottom layer etc, but have a few questions - 

1) what will eventually be the baking floor bottom (the base two pieces) is quite rough - should we mix up either an adobe oven type clay/sand mixture or refractory cement mixture and coat it? 

2) The pieces fit together, but don't tightly lock or lip/seal like some of the higher end US type kits pieces - when we put it all together - should we coat the oven outside with same oven clay/sand mixture or refractory cement? 

3) We've been discussing pros/cons of doing ceramic fiber / chicken wire wrap versus the vermiculite type approach. I know there is some discussion on the ceramic fiber and inhaling but other discussion that it is safe for use as insulation once installed. 

4) We are a bit confused on the base - I understand that there should be an insulation layer in the base - for example sand and glass bottles - but then other postings state should be a weight bearing concrete or wood layer over that I believe and then perhaps fire brick? Our thought was to use cinder blocks to build the base up a bit height - with cement / rebar - then perhaps a weight bearing wood layer (large posts) then perhaps mineral board and firebricks - laying the oven on top of firebricks. Would this work - do we need a sand/glass type layer - instead of the cinder blocks/cement perhaps? Also it seems from reading one of the sections on vermiculite, some people do foundation, concrete slab?, then insulation, then another slab? 

Thanks - any help would be great- I am sure in Italy people install the type of oven forms we have all the time - but I cannot find much anywhere about it online and it is just enough different.

joc1954's picture

Answers to your questions:

1) I would definitely use fire bricks or tiles 30 to 50 millimeter thick. I would just lay down them in a sand bed so you can easily replace them when they will crack. This way you enable them to extend and contract due to thermal changes. Below the sand bed I would put a 100 millimeter thick layer of mixture of vermiculite and cement as insulation. Using any kind of coat is by my opinion not a good idea as it will be soon when the holes will develop and you will have an awful bottom area. Have seen this many times.

2) Use refractory cement for gluing them together and also put some outside, possibly enforcing that with a chicken wire otherwise all joints will crack very quickly. Don't use clay as it will crack during drying  period.

3) I have used this kind of insulation: first 10 cm thick layer of stone wool, covered with chicken wire and a layer of about 6-7,5 cm thick of vermiculite and cement. This way you enforce the vermiculite layer with chicken wire. Then you can apply whatever you want on the top of that vermiculite layer like a lime putty or whatever fits your ideas for final outlook.

4) I have always used the following approach: concrete slab, 10 cm thick slab of vermiculite/cement mixture and I lay then fire bricks/tiles on top of this insulation layer and then I start building the dome - in your case you put your prepared parts of dome on top of brick layer.

Here are links to my three projects:

1.) Using prefabricated parts like in your case - see the photo gallery for details any you will see the insulation layer as well.

2.) Building from scratch - same bottom insulation layer - see the photo gallery

3.) Earthen oven built this year:

Hope this will help you making better decisions.

Happy oven building!