Outward pressure on hearth forms

[james]

I wanted to ask builders what they thought about the outward pressure of the concrete hearth and possibly the vermiculite layer, on the hearth forms. I know that some early verisons of the Pompeii Oven plans called for staps and/or braces to keep the hearth from buldging out, but if you are using 2"x4" studs, I am not sure the outward pressure is enough to require the extra supports.

My concerns is that new builders are putting a lot of time that might not be necessary into supporting the hearth form.

Any comments?
James

[CanuckJim]

James,

From a professional point of view, it's probably not necessary. Still, many builders will be inexperienced, and adding the bracing is a certainty and safety issue that's probably worth the effort. My two cents.

Jim

[Chris]

I used 2x8, with concrete in the lower half, and perlcrete in the upper half. I nailed some little gussets in the corners just to make sure nails didn't get pulled out. I didn't notice any bowing of the forms at all.

I did make my concrete with a minimum of water, so it pretty much stayed where I put it, and didn't try to push too hard on the forms.

[Hendo]

James,

I think it would depend on many factors - the volume of the slab which generates the forces which will bend the formwork, the thickness of the formwork, and the length of the timber, would be the major ones.

My formwork consisted of old 8" x 1¼" fascia & barge boards which were on hand, and as I didn't want to trip over angled bits of timber during the pour, I used some 1mm wire, threaded through the timber forms from one side to the other and tensioned, to prevent any bulge.

Worked a treat!

I shall explain this better with pictures in the 'Brick Oven Photos' section shortly - as soon as I can get my head around the intracacies of photobucket! Stay tuned.

Paul.

[james]

All good points. No sense cutting a corner, and having a problem to deal with later.
Thanks.
James