Another Hearth Question

[maver]

I guess for the straps I'm more concerned about how the corners are fastened, and the straps are so easy in that regard. I don't think the straps do much to prevent bowing (they might even worsen it if your wood has a lot of bow, think violin string) but if you have a 2x6 or 2x8 that has some twist to it you can drive it square with the straps (I used 2 to bring both top and bottom corners into alignment). You certainly can use the straps later when you pick up materials for the finishing of the project with your neighbor's old pickup . However, conventional concrete form nails are cheaper and should hold.

[christo]

hearth thickness

It seems like we are talking about several different issues on this thread.

It sounds like the 2x8 is great if you are pouring a 3 1/2 thick slab followed by 4 inches of insulating concrete. - but you won't have any overlap down on the blocks of the base.

If I'm using the super isol, then a 2x6 or 2x4 is fine (5 1/2 or 3 1/2 thick pour) and can wrap the outside of the base blocks if I wish.

Now the question for MArcel, did you go with a 5 1/2 inch thick pour for a little extra support? In the wisdom of the list - is 3 1/2 enough without the insulating concrete - I did not think the insulating concrete mixture added much if any strength.

I have paint on the ground and am digging footings this weekend!!! - I'm behind schedule already.....

[CanuckJim]

Straps

All,

One comment about strapping forms from an old hand at concrete pours. The rule is: if you don't do it, it will bow. If you do, it won't. I'd take the extra time to support the centres of the 2 x 8s to counteract any possible distortion. If the form boards do bow at all, it will create a lot of headaches down the road with facade treatment, etc. Not worth the risk, and you can't do it once the concrete has been poured, either.

Jim

[Marcel]

Hearth Slab thickness and order of the layers.

It seems like we are talking about several different issues on this thread.

(C) It sounds like the 2x8 is great if you are pouring a 3 1/2 thick slab followed by 4 inches of insulating concrete. - but you won't have any overlap down on the blocks of the base.

(C) If I'm using the super isol, then a 2x6 or 2x4 is fine (5 1/2 or 3 1/2 thick pour) and can wrap the outside of the base blocks if I wish.

(M) It sounds, just above, that you would be resting your form boards *ON* the concrete blocks if you were using less than 2x8s. If so, and you are OK with the consequent lip, go for it. My choice would be the 2x8s because I would only pour a 5" or 5 1/2" thick hearth slab and the additional cost for the deeper form boards is probably less than $20.

(C) Now the question for MArcel, did you go with a 5 1/2 inch thick pour for a little extra support?

(M) I went with the 5 1/2 inch thick pour because that was the recommendation in the original Forno Bravo plans. I first poured about 2" of perlcrete and followed that with about 3 1/2" of refractory mortar.

(M) I'm happy with the thickness and the traditional order of the layers: Insulating on the bottom, refractory layer on top. I feel the order of the layers depends on the builder's priority concerning the emphasis on either pizza, or bread. I was OK with waiting longer for achieving the high heat for pizza but retaining that heat for baking bread and rolls.

(C) In the wisdom of the list - is 3 1/2 enough without the insulating concrete - I did not think the insulating concrete mixture added much if any strength.

(M) "Wisdom" is in my view and in this context, a subjective term. I agree that the insulating layer, irrespective of whether it is on top or bottom, lends relatively little strength. Perlcrete is filling the role of the insulating boards and certainly those boards add almost no strength.

(C) I have paint on the ground and am digging footings this weekend!!! - I'm behind schedule already.....

(M) Then you better stop reading my meanderings and get to work.

Ciao,

Marcel

[dalucca2003]

I am glad I asked the question about the frame....the consensus certainly looks like it is best to place the frame for the hearth around the block stand versus on top of it. If I do go with the straps I have seen posts mentioning they can be purchased at WalMart. Is there any particular strap or straps I need to look for and how many are needed?