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Archena 11-22-2008 06:41 PM

Dumb Question Number 273
Okay I've never really been very clear on how this works, but I finally got the guts to ask. After you poured the base and it's cured, and it's time to take the form off what happens to the bottom of the form? My guess would be that it just stays there, but I'm really not sure.

Okay you guys can start laughing now...


christo 11-22-2008 06:56 PM

Re: Dumb Question Number 273
No laughing here. There many ways that can be had here.

Me - I used concrete backerboard as the bottom of my form and left it inplace. Others use metal sheeting in a similar fashion.

Others use plywood and leave it in place. (not advisable - it will eventually come down...)

Others use plywood and remove it when cured enought to support.

I'm betting there are other variations out there.


Les 11-22-2008 06:57 PM

Re: Dumb Question Number 273
I'm not quite sure what you mean. My plywood was braced from the bottom -when I kicked out the braces, the plywood came down with them.


Archena 11-22-2008 07:10 PM

Re: Dumb Question Number 273
Cool idea, Christo! I hadn't even thought of concrete backer board. That would work perfectly. I could bolt it into the support beams which would tie the thing together better.

I don't understand what you did Les. Wouldn't the base of the form have to be on the edges of the stand?

Modthyrth 11-22-2008 08:28 PM

Re: Dumb Question Number 273
I think there's a good picture of what Les did in the pompeii plans pdf. Yes--I found it--take a close look at the pictures on page 23. Build a brace just inside the block stand, and set a plywood floor on top of the form. It doesn't overlap the concrete block, but rather snugs right up to the edge.

Me, I used the backerboard solution, too. It required less precision and was very easy.

james 11-22-2008 09:40 PM

Re: Dumb Question Number 273
If you want to leave the form in place, use concrete board or hardibacker. Don't leave plywood permanently in place under the concrete slab. If you want to use plywood, you can cut the plywood to fit the opening, and it will fall down when you knock the form out.

Both methods work well, so it's up to personal preference. I used hardibacker on my last oven, and set it on top of the concrete block stand in order to leave it in place. That might be a little faster.

RTflorida 11-22-2008 09:56 PM

Re: Dumb Question Number 273
I used the Hardibacker, cut to fit the inside of the stand and 2x4 bracing that I kicked out after it had set up. The Hardibacker is still in place (20 months later) and seams to be permanently bonded to the support slab. I usually give it a couple of taps when I'm pulling wood out from the base.....has a solid sound, not hollow - A hollow sound would lead me to believe it had lost its bond.
I'm with James, if using plywood pull it out - it is just going to eventually rot from the contact with the cement.


Les 11-22-2008 10:55 PM

Re: Dumb Question Number 273
1 Attachment(s)

Here is a pic (the best I can find right now). I just ran the plywood as close to the block as I could. I used a strip of tape to keep anything from leaking through. Knowing that I was building the oven on top of 4 inches of insulation, I had to make my hearth even with the top of the block. Totally different approach, but it seemed to work.:)


Archena 11-23-2008 05:53 AM

Re: Dumb Question Number 273
Okay, guys, cool! I finally see what you mean, Les. That's pretty neat.

One of the reasons that I asked was because it seemed like a very bad idea to leave the plywood in place, but I couldn't think of any way to get it out. Also I want make sure that I tie the stand and the slab together securely - watching the slab and the oven slide off like Humpty Dumpty strikes me as a very bad thing!

Thanks guys!

bturton 11-23-2008 02:13 PM

Re: Dumb Question Number 273
Thanks for that question! Thanks too for the answers. We're trying to pour our table tomorrow and a lot of our conversation today has been about removing the plywood later. My husband is on the way to Home Depot for some concrete board right now. You guys are da' bomb!

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