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dsgreco 11-10-2009 05:41 PM

The Greco's WFO - Long Island
 
2 Attachment(s)
I have spent months reading on the forum and have finally started my build. Attached are pictures of the stand. I plan on filling the cores and pouring the hearth this weekend.

I have a few questions....

I plan on leaving the angle iron the way it is in the picture. The weight of the concrete board and the hearth poured over and around it should hold it in place. I dont see a reason to recess it into the concrete block. Does anyone see a problem with this?

The hearth will be 3.5 inches of concrete. I am not using an insulating concrete on top of that, I do plan on using the FB board placed after curing.

I am using 1/2 inch rebar about every 10". What is the best method to raise the rebar to the proper height within the hearth when pouring the concrete?

I left the rebar within the stand about 1.5" above the top so it will tie in the stand with the hearth.

When pouring the hearth, how do you prevent the concrete from leaking out through and small gaps in the form?

Should I rent a mixer to fill the cores and make the hearth, or can I do it by hand with the help of some friends?

glindhout 11-10-2009 05:53 PM

Re: The Greco's WFO - Long Island
 
I don't see a problem with the angle iron -- it usually only gets recessed if you're going to add another row of cement blocks on top, and you're using the dry stack method...

On my hearth, I tied the rebar into the pieces that were anchored in the block cores. To hold up the rebar in the center, you can buy many types of either plastic or wire rebar "stands" at your local home center, or just use a few small pieces of block or brick under the rebar.

To prevent the concrete from leaking out through and small gaps in the form, I just applied a layer of painters tape between the form and the top of the blocks... it held fine for the pour, and prevented the drips.

I would definitely rent a mixer... it took over 20 bags (60#) to fill the cores on my base, and about 38 bags to make the hearth. The mixer was a great investment for the $35. rental fee!

jmhepworth 11-10-2009 05:55 PM

Re: The Greco's WFO - Long Island
 
OK, that's a lot of questions. Keep them coming. I'll share my experience and then the experts can weigh in with helpful information.

I don't see anything wrong with leaving the angle iron the way you have it. I did not recess mine into the block and it works fine. I also used concrete boad and liked that a lot more than making a form. You can buy "chairs" for the rebar or just put chunks of brick or stone on them to hold them up. Duct tape keeps the concrete in the form. And concrete is pretty thick. It doesn't flow through a 1/4 inch gap more than to make a mess that you will cover up with finishing material later on anyway. I brought concrete in from a place that pre-mixes it and puts it in a trailer. I still needed a lot of help to get it to the back yard, but it went a lot faster than mixing it on site. And you should be able to fill the cores and pour the slab at the same time. That's what I did.

splatgirl 11-10-2009 06:48 PM

Re: The Greco's WFO - Long Island
 
Technically, the angle iron doesn't need to be there at all, as a rebar reinforced slab can bridge that opening without issue and your slab will be bridging a bigger distance than that across the base anyway. But it won't hurt to have it there and it's one less brace piece you need to cut for your formwork.
BUT...I think a hearth slab that is only 3.5" thick is a bad idea structurally, especially with that rebar spacing. Why only 3.5"? IMO, it's not worth taking a chance with that thin of a slab when it's what the whole rest of your build depends on. For reference, the minimum thickness for a sidewalk, driveway, patio, etc (which do not bear nearly as much load as the literal ton of bricks and mortar that will be your oven), is 4", keeping in mind that delivered ready-mix is typically of a higher and more consistent quality than what you'll get with bagged mix.
Another inch or two is basically the same amount of work and just a few more bucks. If you proceed with your plan for that thickness, I would add rebar mesh and decrease your bar spacing to 6" grid.

Getting your rebar grid suspended in the slab is harder with a thinner slab, but the "professional" method is typically just to pull up on it a bit once you've got some concrete in the form to get it up off the bottom. This also has the effect of getting mud to flow into any voids that may be around/under the bar.

Rent the biggest mixer you can haul. You'll still be in for a bunch of really physical work, but a lot less than trying to mix 40+ bags by hand.

Small gaps in the formwork, up to 1/2" or more won't matter. If they do, you're mixing the mud way too wet.

dsgreco 11-11-2009 07:22 PM

Re: The Greco's WFO - Long Island
 
I had planned on making the slab 3.5" due to the fact that the 2x4 i have is really 3.5" and that is what i was going to use to make the form. I have now reconsidered and think I will go thicker. I am thinking 5-6". I will just have to pick up a few pieces of wider wood.

glindhout 11-12-2009 07:48 AM

Re: The Greco's WFO - Long Island
 
1 Attachment(s)
I think that's a really good idea -- pick up (4) 2x6 at your local home depot, and you'll be much better off -- I think most of us had a slightly thicker slab than you planned. I ended up going 4.5 inches, and just positioned the boards 1" below the top of the block.

Greg

jmhepworth 11-12-2009 10:56 AM

Re: The Greco's WFO - Long Island
 
I used 2x6s to form the hearth stand pretty much as Greg describes it. The other thing I did (as recommended by my concrete contractor friend) was to drill a hole through the 2x6 on each side of the frame and ran some wire back and forth through the holes on each side. I used pieces of scrap rebar to hold it in place and then twisted the rebar to pull the sides in. That eliminated the tendancy of the form to bow with the outward force of the concrete.

dsgreco 11-12-2009 01:38 PM

Re: The Greco's WFO - Long Island
 
I picked up 2x6 and an extra roll of duct tape today. I also rented a small mixer for the weekend for $45. I have a long strap with a ratchet to wrap around the form to prevent bowing. I will post more pics after the weekend.

Thanks for the advice everyone. This forum is really a very good thing.

dsgreco 11-16-2009 10:31 AM

Re: The Greco's WFO - Long Island
 
3 Attachment(s)
The hearth pour is complete! I sprayed the hearth with a little water today and covered it with plastic. The hearth sounded alive, like it was drinking the water when a misted it . Hope that was ok. I checked to see if things remained level, which they have. I attached a pic of the support i used under my backer board. At first I had one support, but added the second when I noticed a slight sag in the front about 1/2 way through the pour. I am not sure why I didnt add the second support in the first place. Things seem to have held fine and are level so I think I am ok. I am not sure who on the forum came up with the idea to use the strap, but it was a great idea to hold the form together. Thanks.

Dino_Pizza 11-17-2009 05:08 PM

Re: The Greco's WFO - Long Island
 
Looks great Greco! I waited 5 days for curing, broke off the forms and started measuring out the center lines, where the oven center will be, where the arches will be...etc... You'll referring to often to that center chalk line (or permanent marker or etched in mark) for the center of the oven floor, both arches, finding the middle-line for the chimney and so on. Since you've got a cool corner hearth (I love that look) you'll want to be accurate.

I've been happy with the 2" FB board so I know you will be as well. Good job on the rebar too. I can tell you'll have nice oven already. Cheers, Dino


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