A Question...

[JoeT62]

I am looking at a full day tomorrow to get some work done.

This may sound silly, but I was wondering if it was OK for me to pour the first layer of the hearth on the same day that I pour concrete into the block stand holes. Or should I let the block stand "pillars" cure a bit before proceeding?

[maver]

As long as you don't have concrete running out of the bottom of your pillars you should be good to go

[Unofornaio]

From a structural standpoint this would be the preferred way to go. in addition putting in some "L" shaped rebar that tie into the slab steel and sit in the webs would be extra insurance. Actually, a slab sitting on the blocks as a monolithic pour should never go anywhere because it is "keyed" into the block webs. But if it was me if I had some left over rebar scraps say 2' long (kinda short) or ideally 3' long I would bend them at a 45 and do as above. To bend them take 2 pieces of pipe (about 18" each) slid over the rebar piece make them meet at the vertex (corner of the L) stand on one and lift the other one while keeping the pipe ends together and you will get a perfect bend every time.
IF you have it left over, if not don't sweat it, it will be just fine.

[ihughes]

Great question, I've been thinking the same thing, particularly since bad weather and a combination of public holidays and broken tools have cost me a couple of weekends' work. So I think I'll do the same thing to save time and enhance stability.

The plans call for rebar in the hearth, but I have some wire mesh left over from the foundation. Could I use this instead?

[wlively]

You need rebar in the hearth slab because concrete is weak in tension. The hearth slab is spanning the opening across the blocks unsupported, which puts the lower half of the concrete slab in tension.

[JoeT62]

Well, after all was said and done, I got the block stand holes filled and made the forms, and then.....ran out of steam!

[Hendo]

I can identify with that! I planned to pour both simultaneously, but decided it might be easier to do two pours on separate days. In the event, we spent so much time rodding the concrete down the block holes, I would have paid a premium for the concrete delivery guy to wait, and wait ...

The other advantage to breaking it up into two pours was that the job was probably easier without all the slab formwork in place that we would have had to reach over all the time - at least for the holes. And I had some pipes to install for the thermocouple wiring which was best done 'between pours'.

On the structural integrity argument, multi-storey buildings using a reinforced concrete framework get built progressively - columns first then floor slabs - and they seem to stay upright ....

Ian - I used both reo and mesh as well as galv steel flooring to support it all. The reo was purely to tie up the 'legs' of the stand and the mesh to keep the concrete slab sound. I figured it was just easier to use steel flooring and avoid building a disposable wooden form and supports etc. The steel flooring (eg Lysaght's Bondek or Fielder's KingFlor) worked out at $75 for 3 sheets @ 1200mm x 400mm x 1.0mm.

See http://www.fielders.com.au/pdf/RF55_UIG_ds.pdf or BlueScope Steel Australia: Downloads for more info on the flooring. Definitely the way to go in my opinion.

[Unofornaio]

At a 56" span a 3 1/2" slab with 1/2 bar on 12" centers clearly is sufficient to hold the weight of this oven design. Adding the decking in your situation worked for you but for this design even with a 72" span is not necessary and really just an added expense. As far as saving the time in making the slab form and supports I suppose you have a point but adding it strictly for structural reasons is overkill, its just not necessary.

As for the flooring on multi-story buildings. Floor slabs as you mention are rarely structural elements of the building they are simply flooring, the superstructure (steel frame) is holding the building upright and together. in many cases the load of the flooring is suspended via this structure around the perimeter (as in the twin towers) Their span load (in many cases) is transfered to the floors beneath them and ultimately to the foundation of the building through a series of columns and the columns are all tied into the floor slabs via rebar. they are poured separately because of many factors including floor flex as well as building deflection. the cold joint created by the separate pours acts as a point where some movement can occur.

[Hendo]

Originally Posted by Unofornaio

... adding it strictly for structural reasons is overkill, its just not necessary.

Now tell me something I don’t know! Seriously, the whole slab could be supported adequately by the weldmesh alone (9mm @ 200mm centres). The steel flooring was very much an afterthought, by which time I already had the rebar and weldmesh, so I buried them in concrete, rather than having them rust away down the side of the house. Cost of timber here in Oz is prohibitive, and this, as well as time/convenience (great!) was a deciding factor in going down this route.

I wasn’t suggesting that flooring was necessarily a structural element – just that reinforced concrete columns and reinforced concrete flooring usually get poured at different times. I was purely drawing an analogy with filling the block holes and pouring the slab separately without serious structural consequences – that’s all.

[Unofornaio]

Originally Posted by Hendo

I wasn’t suggesting that flooring was necessarily a structural element – just that reinforced concrete columns and reinforced concrete flooring usually get poured at different times. I was purely drawing an analogy with filling the block holes and pouring the slab separately without serious structural consequences – that’s all.

Easy there ...as I stated in the orig post "the decking worked for you" for what ever reason, you say because you already had it and thats fine.

> "Ian - I used both reo and mesh as well as galv steel flooring to support it all"

>"See http://www.fielders.com.au/pdf/RF55_UIG_ds.pdf or BlueScope Steel Australia: Downloads for more info on the flooring. Definitely the way to go in my opinion."
Its was these 2 statement that gave me the impression you were suggesting this is the way to go if building this oven. If I misunderstood I apologize.

I guess i should clarify my statement on the monolithic pour. No it is not necessary for theses ovens (unless a local official is going to require it) actually if you have layed the blocks in the base there really is not reason to even grout them (again unless you are locally required to do so) or you are in CA where you are required to do EVERYTHING and then some. But being in the business for as long as I have you learn that some little extras that don't hurt as insurance.
At the minimum, if the base blocks are layed (with mortar) you could just grout the lintel and the 4 corners even just 1 block thickness down again to key in the slab to the base.
A high benchmark to judge by would be here in CA I was required to have vertical steel coming up from the slab footing all the way through the base. On the 3rd and last course it needed to be a bond beam course which contained horizontal steel and the entire base grouted with 6 sack pea-gravel mix....right..talk about overkill
James sells these ovens in CA so I'm sure he is well aware of the blatant CYA (cover your A@#) building regulations we have out here that vary from county to county and city to city.