Fiberglass Insulation for Dome

[BakerBoy]

My oven dome is made from about 3-4" of clay/sand and 1-2" of perlite/cement. I would like to insulate it further by wrapping the oven in home fiberglass insulation but am worried that the heat will pass through the clay layer and through the perlite burning the fiberglass and that nasty binding. Do you think this should be a concern for my oven or is the 1-2" of perlite/cement enough to block out enough heat from the fiberglass? Also is 1-2" of perlite/cement enough insulation or do I need a second layer of some type of insulation? Thanks

[david s]

Re: Fiberglass Insulation for Dome

I used fibreglass insulation for the first oven I built. It was a cast oven with2" thick walls. The insulation sat right against the walls so must have got pretty hot especially as the walls were so thin. On dismantling the oven there was no sign of deterioration of the fibreglass at all, but some people have reported that the binder burns. Maybe depends on the brand. I found the most difficult part was getting a good shape without the stuff compressing and therefore reducing its insulation value, but this would not apply if you are doing an enclosure rather than an igloo.
If I were in your position I'd be just increasing the perlcrete layer to 4", but keep the mix lean (no more than 10:1) Even at 10:1 you've got more mass in cement than perlite and the cement only reduces the insulating capacity.