Wood Support Frame for Plywood

[james]

Chris and Captain,

These sound perfect. No nails necessary (underneath). Can I convince you to post photos in the gallery? I think everyone enjoys watching ovens go up. Better than a barn raising.
James

[Chris]

I used 3/4 inch strand board (OSB). I cut it into two panels for easy removal. Supported by 2x4 on edge along perimeter, and a doubled 2x4 in the center to support the seam. I used the plastic that came around my load of concrete blocks to line the OSB for easy removal. I didn't nail the OSB to the supports, just let gravity work for you.

My rebar was 12 inches on center, supported by flat pieces of mortar that I chipped off of my recycled bricks. I only had to support three pieces of bar, and the rest was criscrossed on top.

-Chris

[captain]

Captain

I just poured mine last weekend I did not use one nail laid 2x4 onthe flat braced by 2x4 legs 1/2 inch ply make sure you put enough bracing also when pouring concrete spread it around equal and dont make it to wet.

[dalucca2003]

Exactly. Keep the rebar three inches or so away from the edge so it will be entirely encased in concrete, and you'll be good to go. There are fancy things to keep the rebar in the center of your slab, but you don't need them if you are mixing with a mixer, just put down an inch or two, lay down your rod, and finish your slab thickness.

Good luck with your pour: that's a LOT of work.

Thanks dmun....we are going to pick up a yard or less from a local rental facility. I figure maybe a little more money, but less work since I am going with the Super Isol and no need for vermiculite.

[dmun]

rebar

Plywood is down.....onto the rebar. So is 12" on center enough? I am assuming that means the rebar pieces are 12" apart from one another creating basically a 12 x12 square. Hopefully will finish by tomorrow as I would like to pour the hearth this weekend.

Exactly. Keep the rebar three inches or so away from the edge so it will be entirely encased in concrete, and you'll be good to go. There are fancy things to keep the rebar in the center of your slab, but you don't need them if you are mixing with a mixer, just put down an inch or two, lay down your rod, and finish your slab thickness.

Good luck with your pour: that's a LOT of work.

[dalucca2003]

Plywood is down.....onto the rebar. So is 12" on center enough? I am assuming that means the rebar pieces are 12" apart from one another creating basically a 12 x12 square. Hopefully will finish by tomorrow as I would like to pour the hearth this weekend.

[dalucca2003]

Janprimus is correct. However, with adequate bracing below the 2x4 you can prevent deflection. Laying them flat may reduce the chance the concrete board (which I think you decided on?) will fold by increasing the supported surface area for teh concrete board. I think I used about 18 vertical braces and the equivalent to 3 2x6 (rather than 2x4) laid flat per quadrant. Here's a step where you really should just use more support than you might think necessary, you cannot overdo this, and failure would cause problems .

I think I am going to go with plywood versus concrete board. So it sounds like on edge is best and I was planning on going overboard on the supports....you are so right Maver, failure here would be huge.

[maver]

Janprimus is correct. However, with adequate bracing below the 2x4 you can prevent deflection. Laying them flat may reduce the chance the concrete board (which I think you decided on?) will fold by increasing the supported surface area for teh concrete board. I think I used about 18 vertical braces and the equivalent to 3 2x6 (rather than 2x4) laid flat per quadrant. Here's a step where you really should just use more support than you might think necessary, you cannot overdo this, and failure would cause problems .

[janprimus]

framing members

For laying up the hearth on a horizontal plane, the 2x4s on edge will give you way more structural strength with far less deflection.
Chad

[dalucca2003]

I will be framing this weekend for the hearth and am confused as to which way to lay the frame for the plywood. I have two installation guides and one shows the 2 x4 on edge and one shows it laying on its side. For those of you who have already poured their hearths, which method do you recommend and which one do you think will provide the best support?