Round shape

[Neil2]

Re: Round shape

Wooden float for placing/leveling. Metal float for finishing.

Give it a light finish pass just after the pour. Let it sit till it "skims over", this may take 30 min to an hour then give it a final finish.

A common mistake is to float and finish the wet concrete too much. If you work wet concrete too much it will segregate. The larger stone particles will sink or be forced down while the fines and cement will come to the surface. This can result in a weak surface layer that may be prone to spalling. Just work and vibrate enough so that all the voids are filled and the surface is level.

If you don't have one, you may also want to buy / borrow an edging tool:

[Wiley]

Re: Round shape

I'm going to jump in here in hopes that you see this before you pour.

Rebar does NOT GO IN THE CENTER OF A SLAB!

In the center of a slab the bending moment is neutral. Concrete is good in compression and bad in tension. Rebar is good in tension so is placed where the slab is in tension.

Place the rebar at the 1/3 up from the bottom of the slab. If this comes too late it probably will still be OK as these slabs are so over designed that it should not be a problem.

Wiley

[Neil2]

Re: Round shape

Even if it is in the middle, the steel will go into tension well before the concrete reaches its compression limit.

Placing it in the middle optimizes the concrete cover which may be more important. Slabs on grade have a very complex and indeterminate bending profile, placing the rebar in the middle is the best.

[Wiley]

Re: Round shape

Neil2,
It's not the "compressional limit" it's "tensional limit" of the concrete. Rebar in the center of a slab simply holds the pieces together after the concrete breaks. To state: "If you are pouring a 4" slab then the rebar should ideally be placed at 2" (the middle of the slab)." is incorrect.

Here's a reference , please see page 128 section "Right position for steel"
Popular Science - Google Books

In fact the whole article is good, well written and easy to read and one I would recommend to forum members not used to working with concrete.

This is not worth anyone getting their backs up, for like I said the design of the stand is overkill. It's designed so that somebody could mess up a bit and still have a structure that works.

Bests,
Wiley

[david s]

Re: Round shape

Just to throw another spanner in the works, I gave up using rebar about a year ago and now use reinforcing fibres, of which there are many, to reinforce concrete. They simply mix in randomly throughout the slab. Much easier to work with and makes the concrete incredibly strong.

[stoveup]

Re: Round shape

David S - how does the cost of using fibers compare to the cost of rebar? Might be different here in the states. THX

[rodeair]

Re: Round shape

Here in my part of Florida, fiber added to the concrete is $6 per yard extra. The way I understand it though, you can skip the wire mesh with fibercrete, but rebar is still necessary for the load bearing areas. Also, it's not particularly good for areas around a pool, for example, because the fibers will eventually stick up on top of the slab.
Leigh

[david s]

Re: Round shape

Not sure about the cost comparison. I use plastic fibres for reinforcing concrete, I've seen steel ones rust that are near the surface, but you can remove any that are near the surface, or use stainless steel. Our local council uses fibres instead of steel for all footpaths. When I buy it ,it comes in a pack that will do one cubic metre. Saves lots of time and you don't have to worry about tying in steel and it's placement.

[Neil2]

Re: Round shape

The rebar contributes to the strength only when it begins to go into tension from bending. Even in the middle, it will go into tension well before the concrete starts to fail from compression.

For any slab or beam design, the "tension" strength contributed by the concrete is too low to be considered.

Typically, a slab on grade is indeterminate. You cannot predict with certainty which parts of the slab will subject to positive or negative bending (a pizza oven slab may be more likely to have negative bending !). Put the steel in the middle and get the benefit of more cover.

[Wiley]

Re: Round shape

Neil2, please look at Mike D's photos in posts #46, #53 or #58. The slab in question is in fact not a slab on grade; but rather is an elevated slab supported by its periphery. The bottom is in tension and the top in compression. In post #60 Mike D's final line, "Anyone have any advice?"


So put your rebar where you want to put your rebar...it is not my WFO. Like I said, these WFOs are designed to be built by an average laymen without extensive skills or knowledge and still work well.


Success or failure does not reflect upon me, unless I give bad advice or suggestion. Praise for success goes to the builder, for the final decision in any aspect of construction is his. Should one not wish my advice one is free to ignore, no cost, no obligation, and rest assured they won't hurt my feelings.

Bests,
Wiley

[Mike D]

Re: Round shape

Hey Guys-

Thanks for all the passionate advice. Keep it coming. I did end up pouring over the weekend. I had a mixer and a two helpers.

The rebar was slightly below being in the middle of the slab. I think it was at a good level.

Thankfully I decided to pour the slab for the Pizza oven first (it was taller and harder to do), because I had only 3 bags left and would of run out mid way if I poured the grill first. (I had to get 9 more bags for the grill) I way underestimated how much concrete it took to fill the blocks.

Right as we were finishing the second slab (way easier/lower), it started to lightly rain/mist. I put a couple of tarps over the slabs to let them set up before wetting them down. It then rained all day Sunday (we did the pour on Saturday).

Here are some pics

-Mike

[lwood]

Re: Round shape

Looking good Mike....Go Bears!

[Neil2]

Re: Round shape

"The slab in question is in fact not a slab on grade"

Sorry Wiley, my fault. I was thinking about slabs on grade.

[Mike D]

Re: Round shape

Ok-

So everything look like it's going fine, I now have a dilemma. I want to buy the 36" kit from Forno Bravo for two reasons, I want to support the people who put up this forum, and I really like the big floor tiles (no one in my area has ever heard of large firebrick tiles), but there is an issue.

- The Kit only comes with 120 bricks for the dome and vent. I have counted the number of bricks people have used for a 36" oven in many pictures and it seems to me that 120 would not be enough (as well as people saying that they went way over what the plans call for). The dilemma is FB say they will not sell just bricks. I asked the woman on the phone "if I bought a kit and I ran out would you sell me a few more?" the answer was still no. It would seem that one would want the same supplier of brick to be consistent (they won't tell me the brick manufacturer, I understand that).
This seems strange right?

-dmun? James? (not trying to go over any ones head or call you out)

-I don't want to have to buy the bigger Kit if I don't need all the stuff. I was going to drive down there and pick it up myself (I'm not that far away- and the shipping was way too expensive). As well as the 43" kit will not fit in my truck (too heavy).

Thanks
Mike

[Mike D]

Re: Round shape

So -

I didn't get any response for the last post, so I think I will go ahead and drive down there and pick up a 36" Kit. The large floor tiles make it worth it. I have worked with pizza ovens in my previous profession (cook) and they all have large floor tiles. A friend of mine built barrel type oven with a normal fire brick floor and it works fine, but I love the look and feel of the big tiles. I went to pick up a few fire bricks for my grill build and they seem really uneven. I can see why some people have had a hard time leveling the floor.

Mike-