Insulating slab with Super Isol

[dalucca2003]

I think of the concrete board as a permanent form. It's sole purpose is to hold the concrete in place while it cures, but unlike plywood, that you cut to fit and then drop out of the hearth after the concrete dries, you can lay the concrete board on top of the block stand and leave it there.

Both are good methods.

James

So do you think it would be okay once finished framing for the hearth to place the cement board inside the frame on top of the blocks as well. Or would it be better to have the cement board only inside the stand opening as one would do with plywood.

[james]

I think of the concrete board as a permanent form. It's sole purpose is to hold the concrete in place while it cures, but unlike plywood, that you cut to fit and then drop out of the hearth after the concrete dries, you can lay the concrete board on top of the block stand and leave it there.

Both are good methods.

James

[maver]

support

the rebar and concrete layer are the support, once the hearth cures at least a week. The lumber frame support for durock or plywood do the job until at least a week. The durock is flimsy and provides no real structural support.

[dalucca2003]

So with the Durolock and of course rebar, there is no additional support under your hearth?

[mrpbjnance]

I used the durolock cement board in place of the plywood and had it sitting on top of my blcok stand making it permanent. I had some 2x4 braces for temporary braces. I poured a 6" thick hearth which I put the Super Isol on Top. I carefully watched the durolock during the pour and there was no sag at all.

[dalucca2003]

Hello

What is the best method to install the iso board? I see the glue being sold, but I was wondering if mortar would be OK? What are most people doing?

In reply to the previous post, you don't need the pier. I just poured my hearth 2 days ago and used 1/2" Durock cement board. My inside opening was 55" x 72" and with 3 2x4's equally space, running long ways, I had no problems what so ever. Did no even detect sag.

Thank you,
Wade

Question....are you utilizing the Durock cement board in place of plywood and is it permanent. And were the 2x4's temporary while the hearth was curing?

[dalucca2003]

Can you then able refractory mortar directly onto the Super Isol boards?

[james]

Installing Super Isol

Hello all,

I moved this thread to Getting Started. It seems more appropriate.

You can attach Super Isol with either refractory mortar or glue. I talked with the producer, and they said either would work. The glue is convenient. The blocks are square and rigid, so you just fit them together and hold them down from below with glue or mortar. The board gives you a nice smooth and flat surface for assembling your oven.

James

[wlively]

How to install

Hello

What is the best method to install the iso board? I see the glue being sold, but I was wondering if mortar would be OK? What are most people doing?

In reply to the previous post, you don't need the pier. I just poured my hearth 2 days ago and used 1/2" Durock cement board. My inside opening was 55" x 72" and with 3 2x4's equally space, running long ways, I had no problems what so ever. Did no even detect sag.

Thank you,
Wade

[mrpbjnance]

A reminder; if you block in the back section completely, you need to put in a vent. If the point is just additional support, you could just add a stack of blocks on each side, and still have the additional wood storage. Remember: the oven distributes most of it's weight to it's edges. Just building a pier in the center wouldn't be that useful.

Other than that, your plan sounds good.

Thanks Dmum! The main reason I was going to buid a pier in the center was to support the concrete backer board (with additional framing I will remove) during the pour. I understand that most of the weight is around the outside of the oven but if the 4" slab will support the oven alone I suspect that the middle pier will help a bit.

Thanks
Mike

[camarina73]

layer of super isol and 2" of vermiculite

I wanted to put 4" of concrete super isol and 2" of vermiculite in that order. That will put my top of landing at 42.5". Two questions. 1. Is that to high? and 2. Can I pour the concrete slab, Put super isol on top with no adhesive and then pour the vermiculite over? I wanted to do this so I would not have to adhere super isol to vermiculite layer. Please let me know your thoughts thank you.
Carlo

[dmun]

A reminder; if you block in the back section completely, you need to put in a vent. If the point is just additional support, you could just add a stack of blocks on each side, and still have the additional wood storage. Remember: the oven distributes most of it's weight to it's edges. Just building a pier in the center wouldn't be that useful.

Other than that, your plan sounds good.

[mrpbjnance]

adding a center section

I know its not necessary but I am leaning toward adding a center section of blocks to support the middle of the slab. I also plan on usig concrete backer board instead of plywood and just leave it there.
So I will pour the slab on top of the backer board and then put the super isol on top of the slab..then the oven on top of that.

[Alan]

Rebar can be placed in different locations in the slab according to the size of the slab and the loading. It will generally keep the parts of the slab from separating if it cracks, and can make it stronger as well. A slab that's resting on its edges and loaded at the center will be in tension on the bottom and in compression on the top (think of the slab sagging a very tiny amount with the top concave and the bottom convex - this is how the slab will move, though the movement will certainly be too tiny to see).

Concrete is much weaker in tension than in compression, so if the slab were heavily loaded you'd put the rebar near the bottom where it's in tension but be sure, as Alf says, to have enough concrete to protect it from corrosion. I imagine that a 4" slab is very lightly loaded compared with its ultimate strength, which is why people do fine putting the rebar near the center. It still adds integrity and strength to the slab. If it were to begin to crack, the sections are held together and can't go anywhere.

[Alf]

Reinforcing steel should be encased in a minimum of 50 mm (2") of concrete to protect the steel from the elements and thus rusting. That?s according to our Uk building regulations and the fact we live on a generally wet / damp Island.

Alf