question about hearth slab framing

[Les]

Re: question about hearth slab framing

Thanks for all the tips!

Stonecutter, the "legs" are already shimmed to level things out and stabilize, but still it is quite wobbly.

SableSprings/Mike, I've already learned from your past experience, because I was gonna screw some braces to the top to see if that would help - now I won't try this.
I like your idea of the wire...might give that a shot.

NCMan, are you saying you just screwed some of your "legs" to the block stand? I could probably get some tapcon screws (if they aren't too pricey).

Les, I can't honestly picture what you're describing. Got any pics? I know I've been thru your build thread, maybe it is time for a re-visit.

Thanks,
John.

John, I know this is a little late - just saw your request. This is the best I can find. The wood you see is supported from the bottom ( inside the storage area) and is basically floating inside the block. http://www.fornobravo.com/forum/f8/s...arth-1850.html

[almondsurf]

Re: question about hearth slab framing

Nice framing idea...this would have worked for me I think...anyway, I'm enjoying your build thread, learning lots along the way. Thanks for sharing.

My pleasure! Feel free to follow my thread... I'm sure to make lots of mistakes that you may learn NOT to do. Building the oven is fun... Right now I have to be patient as it's drying out, but it's fun.

[Greenman]

Re: question about hearth slab framing

Hello Cook4fun

I would have him make a form and pour the insulating layer in the shape of the oven making sure it is big enough for the dome bricks to sit on the insulating layer. The perlite / Portland mixture is a little fragile so a concrete band around it helps to protect the edge.
My 2 cents worth.

David

Something like this. It also pays to have a hole in the middle of the 'keyhole' so any water that finds its way under the hearth can drain away. This worked for me and is easy enough to do.

[DavidApp]

Re: question about hearth slab framing

Hello Cook4fun

I would have him make a form and pour the insulating layer in the shape of the oven making sure it is big enough for the dome bricks to sit on the insulating layer. The perlite / Portland mixture is a little fragile so a concrete band around it helps to protect the edge.
My 2 cents worth.

David

[johnnybrewmeister]

Re: question about hearth slab framing

Why not use 2x6 boards like I did? It worked great. I had my wife help me hold the boards up. I had them about an inch or so below the "slab" that I was laying. This way I was able to suck it tight to my concrete block to hold it into place. I put 2 screws in each end to hold the boards. I just worked my way around. Put one board up, measured 3.5", made sure it was level as I screwed in my next board. The last joint was a little tough because I had to make sure it was very tight, but I really liked how it turned out. I dont even know if I 'needed' the support boards, but put them there just in case.

I poured my slab just a couple weeks ago. Make sure you have enough concrete, I didn't. Hope it helps.

Nice framing idea...this would have worked for me I think...anyway, I'm enjoying your build thread, learning lots along the way. Thanks for sharing.

[cook4fun]

Re: question about hearth slab framing

Greetings fellow FB fans...a question: I'm having the concrete block for my oven done by a builder, I have provided him all the specs, dimension (WxL) as well as height...I want a 4 inch layer of perlite / portland on the top (ration of 6:1), so here's the Q...should I have him do the entire "top" (measuring 6 x 6) with this mixture, or should I sketch out the dimensions (shape) of my oven, and have him make a frame with that shape, and only fill that in with the mixture, then fill the remainder with "just" Portland (asked another way, if the mixture is all on the top, will there be any wicking of heat / moisture to be concerned about ?

Thanks to all that can provide thoughts or guidance.

PS: I currently live in Germany, and will return home in June, so that's why we have a builder doing this work.

[almondsurf]

Re: question about hearth slab framing

Nothing wrong w/that method at all. The way I described is much easier, faster, less people needed, saves concrete, money and labor. I thought that might interest him.

I guess I can see the utility in that

[NCMan]

Re: question about hearth slab framing

Glad you found a way that works for you. Best of luck!!

[johnnybrewmeister]

Re: question about hearth slab framing

NCMan, my slab is going to be the same size as the block stand, so the form for it cannot rest on top of the stand. So the form is just outsize the top outer perimeter of the blocks, and the "legs" are the vertical supports that hold the form up. I'm pretty sure this is the same as the FB plans call out.

Anyhow, I ended up with a modified version of what SableSprings/Mike suggested - I have rebar extended up from the block cores, that will be in the slab thus tying the two together (block stand and slab). So I drilled small holes in the wood form on all 6 sides and used wire to tie the forms to these secured rebar pieces. Now the form is rock-solid in all directions.

Wonderful source of knowledge this forum is!

John.

[NCMan]

Re: question about hearth slab framing

Nothing wrong w/that method at all. The way I described is much easier, faster, less people needed, saves concrete, money and labor. I thought that might interest him.

[almondsurf]

Re: question about hearth slab framing

Why not use 2x6 boards like I did? It worked great. I had my wife help me hold the boards up. I had them about an inch or so below the "slab" that I was laying. This way I was able to suck it tight to my concrete block to hold it into place. I put 2 screws in each end to hold the boards. I just worked my way around. Put one board up, measured 3.5", made sure it was level as I screwed in my next board. The last joint was a little tough because I had to make sure it was very tight, but I really liked how it turned out. I dont even know if I 'needed' the support boards, but put them there just in case.

I poured my slab just a couple weeks ago. Make sure you have enough concrete, I didn't. Hope it helps.

[NCMan]

Re: question about hearth slab framing

Thanks for all the tips!

NCMan, are you saying you just screwed some of your "legs" to the block stand? I could probably get some tapcon screws (if they aren't too pricey).

Thanks,
John.

John.....No, my forms are not attached to the foundation in any way and there is no need to do so. It's simply sitting on the block and the Tapcons are just there to keep it from shifting. I'm not sure I understand what you mean by "legs". I'm guessing that they are pieces of wood you've added in an attempt to level up your formwork(?) If so, normally they would not be needed, but I will guess again and figure your blockwork is not level? Pictures help a lot on here. Then people can better understand what you are asking about. Anyway, yes, all I used are a handful of Tapcon screws and a few shims, as shown in my photos. That is all that is really needed. I simply screwed my 2x4 forms together, installed my vapor barrier, set the forms on my blockwork, laid my rebar mat in place, added a few Tapcons to hold it in place while pouring and I was ready to pour in about 10-15 minutes. Anything more than that is overkill. Also, it's good that you are planning to pour only 3.5 inches of concrete. 3.5-4" of concrete is all that is needed. No need to do anymore than that. People get way too carried away sometimes. Can you add some photos?

[johnnybrewmeister]

Re: question about hearth slab framing

Thanks SableSprings...you've given me some other ideas on how I could possibly use wire to tie things to areas of my (dry-stacked) block stand that might have gaps I can take advantage of. The pics of how you used wires helps a bunch.

Sharptailhunter - I'll search a bit for your build thread, 'cuz I kinda think I know what you're talking about, but not sure I 100% getit.

Thanks,
John.

[sharptailhunter]

Re: question about hearth slab framing

I used 2x6 boards so I'd have about 1.5" of board skirting around the CMU stand. From your description, I'm picturing that the bottom edge of your 2x4 frame/form is level with the top of your stand? If so, you could easily add 2x4 skirt braces to the bottom of your frame by screwing pieces of 2x4 under the frame by using another scrap piece of wood to scab over the joint, if that makes sense? Just make sure your screws aren't so long that they'd interfere with either your stand or protrude through into where the concrete is going to be poured. You already have the vertical supports in place, so it sounds like you just need to keep the whole box frame from shifting on top of your stand? The skirting can help with that as well as some buttress braces that extend diagonally down and out from at least the middle of each of the four pieces forming your box frame. Personally, I would do both. You're welcome to look at my build thread (42" Idaho Spud) as I just poured my hearth. I didn't use the buttress braces because I had some different forms that gave me stability against the sides of my box frame from bowing out. Not sure if any of that helps...

[SableSprings]

Re: question about hearth slab framing

John, here's some pics I found that show how we did the wire reinforcement through our wobbly form's sides. We were up at Hihium Lake in British Columbia and everything had to be hauled in (last 1/2 mile from the clearing to the house is a barely passable old logging road...Kubota RTV & foot traffic only). That's why you'll note scrap metal mesh pieces used to make up for the lack of more "real" rebar. You can see the wire wrapped around the nails on the form perimeter to keep it tight and also get a feel for why we had a form that was a more little wobbly than most

FYI, the piece of foam in the photo was pushed into a rectangular cut in the cement board and stayed there through the pour. The foam (void form) was removed when the concrete hardened and thereby left an opening through the slab that ultimately became the ash dump slot.