Insulation pad

[Elcho]

The plan is to use Header blocks for the top layer of my foundation.This means the bottom of the block is full 390mm x 190mm x 190mm high size as per standard blocks, but the top half is 390mm x 90mm, allowing you to overlap other materials such as flooring etc in the recess or create a half width top to a wall.

This will allow me to pour the concretre pad and then insulation on top while keeping a nice tidy outside and there is liitle need for boxing.
My question is if I only put the vermiculite pad under the oven base will I lose to much heat if I surround it with normal concrete to fill out to the top of the header blocks?

[brickie in oz]

Re: Insulation pad

Have you got a rough sketch of what you want to achieve?

[Neil2]

Re: Insulation pad

"oven base will I lose to much heat if I surround it with normal concrete"

A sketch would be nice, but if I understand your question you should be OK. The insulation only needs to be under the oven itself (floor, dome wall and dome insulation). It need not and should not extend to the edge of the slab.

I do suggest that this insulation layer be provided with positive drainage and some ventilation through the concrete to the outside.

[Elcho]

Re: Insulation pad

Not sure how to get a drawing in..
But reply from Neil2 sounds like I can do what I am planning.
When you say a vent and drain do you mean run a drain hole through the concrete pad (under the vermiculite pad) and out through the base?
Just one? or more.
Would a small PVC pipe do the trick or better with steel pipe

[Neil2]

Re: Insulation pad

I have 4 - one inch pvc pipes at slab level running from my insulation through my concrete "belt". If you can set these down into the slab pour. If your slab is already poured then slice a bit off the pvc lengthwise so that sits flat. To keep bugs out, I used the following (called soffit vents)":

[david s]

Re: Insulation pad

I do the same, but I just glue some insect screen on the inside of the hole.I think it is also a good idea to arrange some kind of vent for the insulation that goes over the dome.

[GianniFocaccia]

Re: Insulation pad

I built a 5 1/2" cavity into my support slab (4" thick) and filled it with vermicrete topped with of 2" of ceramic board. Just make sure you have at least 2" of insulation that protrudes outside the perimeter of the dome. If I had it to do over, I'd extend the insulation 4".
John

[Elcho]

Re: Insulation pad

Thanks for all the answers, only poured the foundation pad today. Was surpposed to be a good day, poured it this morning raced into town and did the cam belt on the wife's car and came home to find it raining. So we now have a teepee in the back yard trying to keep it dry.
I will put the drain/vents in when I do the pad. I had been given 4 thermo couples that fit my multi meter I was going to put some in. Where would the best place be to position them?.