fiberglass insulation between concrete and vermiculite insulation layer

[pabsey]

hi i am in the process of building my first oven on a real budget. what if i sandwiched fiberglass bats in between the concrete and vermiculite layer in a pocket so it would not be compressed! make sense?

[Rastys]

Re: fiberglass insulation between concrete and vermiculite insulation layer

pabsey,
assuming (and that in itself can be dangerous), that you are talking about the floor insulation and not the dome, I would check out the thermal/insulating index of the product in question before I made a decision.
If in the floor, then you will have a problem of supporting the hearth over a very compressible and thick material without any other reinforced, strong non heat absorbing material that will support your hearth bricks!
Building an oven on a budget is good but don't take it too far as you will be disappointed with your results and it is at your foundation level.
Do a little more research and use an insulating board or thick vermiculite cement as you have few other options to correct for your mistakes other than to demolish and start again with the proper and recommended materials.
I keep an eye open in this forum and I would hate to have to quote "I told you so" when you report that your oven has collapsed or even just your floor!
Rockwool has a higher insulation index than fibreglass but I wouldn't use either over a board or vermiculite in trying to save less than $100.

For what it is worth.

Rastys

[pabsey]

Re: fiberglass insulation between concrete and vermiculite insulation layer

thanks for the replyi think you misunderstood my idea. there would be the cement slab followed by batt insulation then vermiculite concrete slab supported by bricks to keep it above the concrete by 3inches so the fiberglass would be in a pocket and provide more insulation! or would just another couple inche of vermiculite concrete be just as good?

[Rastys]

Re: fiberglass insulation between concrete and vermiculite insulation layer

The vermiculite cement insulation supported above the fibreglass will not be strong enough to support the brick hearth without collapsing.
Forget the fibreglass and put a little more vermiculite cement to cater for your under floor insulation. Four inches should be fine.

Rastys

[dmun]

Re: fiberglass insulation between concrete and vermiculite insulation layer

You don't want domestic fiberglass insulation anywhere near a high heat situation. It has an organic binder that doesn't withstand heat.

[Neil2]

Re: fiberglass insulation between concrete and vermiculite insulation layer

I agree with Rastys. Skip the fiberglass. Put in more virmiculete. Vermiculite is pretty cheep.

The only "fiberglass" that will take any heat is the stuff they use to insulate kitchen ovens. It is generality about 1 inch thick and has an aluminum finish on one side. You can get this at places that service kitchen appliances. I used it to insulate my oven door.

[Oz Bakery]

Re: fiberglass insulation between concrete and vermiculite insulation layer

I use fiberglass batts over the entire finished concrete structure, and then clad that with sheet metal. It does a good job, while the outer surface is whatever the ambient temperature is, the temp between the concrete and the fiberglass is over (sometimes quite a bit over!) 200 degrees. If you are only baking a load or two it might not make a big difference to you at all, but when I'd bake 3 days in a row it makes quite a big bit of difference.

Having said that, everyone else is correct that you should only use vermiculite or perlite /concrete mixture as the base.