oven slab

[jlaw]

i am about to pour my slab for my forno-bravo type oven. i have a few
questions:

1. do you pour the insulation layer immediately after the structural
layer (ie while the concrete was still wet)? or dod you wait until the
concrete was at least somewhat cured?

2. also, how do you mix the vermiculite / cement / water for the
insulation layer? the forno bravo guide recommends against using a
mixer, and it seems like quite a volume (~0.5 cubic yards) of material
to deal with... do you mix all at once, or a wheelbarrow full at a a time?

3. the plans call for using 2x8 boards to frame the outside of the
slab. this structural layer is 3.5" thick and the insulating layer is
4" thick, so 7.5" thick, which is roughly the height of a 2x8.
however, this means the edge of the 2x8 would be just against the top
of the cinder blocks. i figured it would be better to have the framing
extend down along the cinder blocks somewhat, to help support the
form, etc. therefore, i would think it better to use a 2x10, to have
around 2" of board laying against the top 2" of the cinder blocks. is
there some reason NOT to do this?

thanks!

[Jed]

Morning Jlaw,

Here is my opinion on your questions....

Originally Posted by jlaw

i am about to pour my slab for my forno-bravo type oven. i have a few
questions:

1. do you pour the insulation layer immediately after the structural
layer (ie while the concrete was still wet)? or dod you wait until the
concrete was at least somewhat cured?

Either system works fine. You can add the insulation layer right away, or you can wait.... The wood structure you have built will hold the whole thing up until it cures, and you do not need a mechanical connection between the two layers. So add the insulation as soon as your schedule allows to keep the project moving.

Originally Posted by jlaw

2. also, how do you mix the vermiculite / cement / water for the
insulation layer? the forno bravo guide recommends against using a
mixer, and it seems like quite a volume (~0.5 cubic yards) of material
to deal with... do you mix all at once, or a wheelbarrow full at a a time?

I mixed wheel barrow load at a time. It took several hours working by myself, but I got the job done. I would measure the perlite (in my case) into the wheel barrow. In a bucket I would measure the cement, and add the water and mix the cement and water with a drill and a paint mixer attachment. I would then add the cement and water mix to the perlite and mix with a garden hoe. I ended up with a uniform mix that cured well over time. It takes several days for this mix to get 'hard'.

Originally Posted by jlaw

3. the plans call for using 2x8 boards to frame the outside of the
slab. this structural layer is 3.5" thick and the insulating layer is
4" thick, so 7.5" thick, which is roughly the height of a 2x8.
however, this means the edge of the 2x8 would be just against the top
of the cinder blocks. i figured it would be better to have the framing
extend down along the cinder blocks somewhat, to help support the
form, etc. therefore, i would think it better to use a 2x10, to have
around 2" of board laying against the top 2" of the cinder blocks. is
there some reason NOT to do this?

thanks!

Your proposed system of using 2 x 10's sounds fine.

Keep up the good work and you will be 'in the pizza' before you know it!

JED

[jlaw]

okay - thanks.... so if you pour the insulating slab directly on the wet concrete slab, the 2 layers will stay distinct? the one will not sink into the other?

[dmun]

the one will not sink into the other?

Nope: the light stuff will float on the heavy stuff

[woods witch]

Hey Jeff...good to see you on this forum. I'm also glad you decided to do the pompeii style, Jerry and I think you'll be happier with it! (I just posted that we are ready to cook this weekend and updated our pictures if you get a chance to look at our progress..)
feel free to make another trip out if you'd like to....but you'll find the best advice from far more experienced people here
good luck with your pour!
Carolyn