36" in Seattle

[kebwi]

It begins! It's hard to appreciate from a picture of a hole in the ground just how much effort goes into making such a hole. I haven't leveled it yet, and I suspect I may need to go a little deeper anyway (3" gravel + 5" concrete = 8" foundation, let concrete rise above lawn by about 2" means I need 6" deep level across the bottom).

Important question: you will notice that I am attempting a rather large opening on the right side. The opening on the left side is four half-blocks wide, 32". The opening on the right side is five half-blocks wide, 40". With angle iron and/or an extra rebar right across the lintel position, should that be okay? Remember, I'm only building a 36" oven and I don't intend to build a brick enclosure (going for stucco), so it should be amongst the lightest of ovens.

Thanks.

[KINGRIUS]

Re: 36" in Seattle

Kebwi, the design I used for my oven stand has a 40" opening in the front between block. It has NO angle iron support. It does have two layers of steel mesh with 1/2" rebar grid (similar to your digital model hearth slab drawing). This design is to support a huge barrel vault oven, not a smaller pompeii style oven. I have never heard of a hearth slab collapsing using this design.
I don't see your two gaps being a support problem, especially with your angle iron support.
My $0.02 worth.

Darius

[kebwi]

Re: 36" in Seattle

Well, that's certainly good news. What if I DON'T use any angle iron (but double up the rebar across the lintel)? Does anyone think I would have a problem with that? I would love to skip the angle iron. That ****'s expensive!!! ;-)

Incidentally, it is a little strange to include the interior angle iron when there is not a course of blocks above it. That interior angle iron is essentially embedded in the support slab. Does anyone have any thoughts on that? Since my design has no blocks above the angle iron should I only put it on the external face...if at all?

[Les]

Re: 36" in Seattle

You won't need the angle iron. If you are stacking block, it makes it easy to do. Just make sure you bend the steel into the block (for more pull strength). Steel and concrete is plenty strong - you most likely drive over it every day.

Les...

[kebwi]

Re: 36" in Seattle

@Les:

I'm afraid I don't quite understand. When you say bend the steel into the block, I presume you are referring to the rebar embedded in the hearth. Are you suggesting that the rebar be bent ninety degress straight down into the cores of the wall? I was hoping to do this job without bending any 1/2" rebar? I'm pretty confident I can cut it with a conventional grinder and the right blade, but as or bending it...sheesh...it's half an inch thick!

By the way, I noticed that your support hearth does not rest on top of the block walls, but rather is held up by the rebar extending *into* the wall through slotted blocks. Would you recommend that over the Pompeii directions for any particular reason? I'm open to any ideas on the subject.

Thanks.

[Neil2]

Re: 36" in Seattle

"I would love to skip the angle iron. That ****'s expensive!!! ;-)"

Old bed frames.

"but as or bending it...sheesh...it's half an inch thick!"

Most building suppliers who sell rebar will have a hand operated bending tool in their yard for use by customers. Use 3/8 inch rebar instead of 1/2 inch rebar . This is much easier to handle. Just up the rebar quantity (reduce spacing) by 25%.

[kebwi]

Re: 36" in Seattle

I've read the bed frame hint on forno bravo before. I was weary because, obviously, framing angle iron is much much thinner than the gauge specified in the Pompeii directions.

It'll still work? I mean, I guess it can only help, but the question is, does it serve a purpose at that gauge, whatever gauge bed frames are?

[Neil2]

Re: 36" in Seattle

You don't need the angle iron. Throw a couple of extra 3/8 rebar over the lintel areas. This rebar should be bent down 18 inches or so and concreted into the wall. Also put an extra 3/8 inch rebar in an "L" shape around the "weak" corner. I would make the suspended slab at least 4 inches thick with all rebar near the middle vertically.

Rebar is cheap.

[kebwi]

Re: 36" in Seattle

So something like this?

[Neil2]

Re: 36" in Seattle

Something like that. Make the "L" longer running the full lenght of each side.

What is the spacing on your grid ? I would make it 6 inches or so, with the lintel bars as extras. I am assuming you are using 3/8 inch rebar.

The straight pieces should also be bent down in to the walls or be hooked at the ends.

What graphics software are you using ?

[kebwi]

Re: 36" in Seattle

Well, I had originally planned on using 1/2" since it's the Pompeii prescription and seems naturally stronger. I can go with 3/8" if folks think it will be strong enough for the job. You suggested 6" spacing. I thought Pompeii suggested 12" but maybe you're accounting for the 3/8" being weaker?

Should I use 1/2" for the foundation and 3/8" for the hearth? Or just 3/8" all around to make things easier to work with?

As for the hooks you suggest at the ends, I'll be lucky if I can figure out how to make a clean ninety degree bend for the top. I don't have any pipe lying around. I was kind of hoping to get away with no rebar bending at all on this project. I'm a little worried now that I'm getting all this advice to bend the rebar. I mean, anyone can wrap it around a tree and make a mess of it, but to get a nice tight corner, I just don't know. I need pipe, right? Is there any other way to do it (without a $3000 bending machine)?

Most of my 3D modeling is done with Meshwork. Bryce makes things look prettier but it is virtually unusable for actually building models. Sometimes I make the models in Meshwork and then render them in Bryce if I want a near-photo-realistic appearance, but for this project it hardly matters, maybe for the picture of my yard (in my album) I should redo it in Bryce. I dunno.

Thanks.

[kebwi]

Re: 36" in Seattle

Sorry, I misunderstood you. When you said hooks, I first thought you meant J-hooks at the bottom of the "lintel" bars. Upon rereading your response I now think you meant a ninety-degree turn on every cross-hearth bar, just like the lintels...which means my previous response didn't quite make sense.

Same problem stands though. I need an efficient way to make numerous clean ninety-degree bends.

Sorry for the confusion.

[Les]

Re: 36" in Seattle

I used 1/2 inch spaced 11 - 12 inches. You can go down to the box stores and buy a couple of feet of pipe - it's not that expensive. You do want to bend it and drop it into the cores. I didn't do that, but had my numbers ran through a PE. If I had the bend, it would have added a huge amount to what the hearth could support. Well worth the effort.

Les...

[kebwi]

Re: 36" in Seattle

So on this rebar business, when you suggest bending all the cross bars down into the cores (obviously only the cores that are filled, which is every other core), how far down should it go? I ask because, if it extends all the way to the floor, it seems redundant with the vertical rebar already in the core (as per the Pompeii directions). Should they be separate pieces: full height vertical straight and separate cross-hearth hooked a few inches? Or should it just be one super long piece: up one core across the hearth, and down the opposite core?

Grrr, sorry, I'm not trying to be pedantic. I suspect people will tire of offering advice before I get the best design settled in my mind and at that point I'll just go with the consensus where ever everyone's patience with me peters out. My apologies.

:-)

[KINGRIUS]

Re: 36" in Seattle

You can run the rebar vertically at the corners all the way to the foundation slab and leave about 18" extra rebar sticking up. Pour your four corners and wait for the cement to get good and hard (@least 36-48 hrs). It will be much easier to bend with it anchored in the cement.
I managed to bend my 1/2" rebar with a 4 lb. sledge by leaning one end up on a brick and repeatedly smacking it till the bend was started. But I realized that it would've been much easier to just set it in the cement and let my foundation hold the rebar whilst I smack it over. I you use 3/8" it'll be that much easier.
You can use the wire ties and tie these vertical bent rebar to your horizontal grid. I hope that makes some sense.

Darius