Round shape

[Neil2]

Re: Round shape

I hope I'm wrong, but I fear your slab will crack at the "jog" within two weeks. This is not a structural concern, only an aesthetic issue.

If it hasn't cracked yet, you could cut a 1/4 to 3/8 inch deep construction joint across the slab at this point using an angle grinder.

[Mike D]

Re: Round shape

Why would it crack? What would a 1/4 to 3/8 inch cut do? I would prefer it to not crack.
Should I really do this?

Thanks

[RTflorida]

Re: Round shape

All larger (smaller too, to a lesser degree) concrete slabs crack. Think of a sidewalk or driveway. Those relief cuts (done with a special trowel before it sets) are there for a reason - to encourage the concrete to crack there, as apposed to a random, crooked, and unsightly crack. Is it affective? Yes and no.
Not here in Florida, there is so much soil movement due to the water table being so high and all of the sand, the only warranty anyone will give is against cracks wider than 1/4". Anything else is considered normal...in any concrete pour.
I would make the cut, it certainly won't hurt and may very well help. Will look better than a crooked as a dog's hind leg crack.

RT

[Mike D]

Re: Round shape

Ok- so I cut a 1/4 inch line at the L, I hope this will help. The concrete was not that hard yet. Most of it will be covered anyway, and the cut was not that ugly. Thanks for the heads up guys.

Mike D

[Neil2]

Re: Round shape

Concrete shrinks as it cures. The "inside" corner created by the jog in the slab will concentrate the stress at the corner and the crack will propagate from there.

The construction joint, created either by a separate pour, troweled in joints or a cut will control the cracking to the joint (hopefully).

As RT notes, most slabs will crack but any slab that has an "inside corner" are more likely to and should be designed with a construction joint.

[Mike D]

Re: Round shape

NO cracks yet, cross your fingers. Maybe the cut helped, but it has been raining all week off and on. I have kept it wet and covered until today. Starting to lay out the first course of blocks and counting how many more I will need.
How long should I really wait to build on top of the slab?
-Where have people been getting the 2" x 2" x 3/8" angle iron? HD doesn't have 3/8". Do I need to go to more of a prof store?
Thanks
Mike

[azpizzanut]

Re: Round shape

Hi MikeD,

It isn't 3/8" thick. I used angle iron from a bed frame that is 1/8" thick and the store bought angle iron is only slightly thicker. HD is often out of stock but if you can't find an old bed frame then try a welding shop or metal yard or junk yard. You're not holding up much weight and you can put in front of the block and another in back, then stand on it to prove to yourself that it won't break. When the slab cures there is not as much stress on the metal. If you are using it for the chimney transition then the choice is yours, but again you don't need 3/8" thick metal.

Cheers,

Bob

[Mike D]

Re: Round shape

Thanks azpizzanut-

I'm just following the plans? I didn't understand why it says 3/8 ". It seems like 1/8 " is plenty strong. Anyone else use 3/8"?

How long do I need to wait to build on the slab?

[azpizzanut]

Re: Round shape

MikeD,

Most builders keep their slab covered and wet for a week or at least a few days. I wet mine and kept it covered for five days before dry stacking the blocks. Your slab has been down long enough that you won't have problems. Some guys build on their slab in just a couple of days. I'd prefer to wait and gather up all the other items I need while wetting the slab regularly for a few days.

Best of luck,

[Mike D]

Re: Round shape

Ok-

So I built the block forms. I decided to mortar them together just to give them a little more connection. They just felt a little unstable and wobbly as well as it gave me a chance to level it a little bit more. I decided to not use the angle Iron over the entry as you guys said (in a side post "angle iron 3/8?"). I like the idea of having a bigger opening. As you can tell I put a middle row of 6x8 blocks to give the slab more support. The bond beam blocks on the top row will give everything a little more connection (am I over building this thing yet?).

Now comes the rebar, I will try not to go overboard.
I was going to use Hardibacker on the bottom of the slab. What thickness do I need, 1/2 or will 1/4 work fine? Do people glue it down so it doesn't move when you pore?

The side structure (picture #4) is a grill that I am rebuilding (I demoed it before the build with the intention of redoing it better). Basically a slab will go on like the oven, then a open brick form around the outside with the front open. All of the bricks will be on top of the block structure and only a layer of fire bricks (no mortar) on the floor. I use 2 Tuscan grills side by side, it works great.

What do you guys think?

Thanks
Mike

[azpizzanut]

Re: Round shape

Hi Mike D,

You can use plywood for the form to fit inside the blocks but you'll have to cut out for the center support. Make up some 2x4 supports to hold up the edges and at center in front and make up some tapered shims so you can adjust the height. I used Hardibacker board for mine and overlapped the edges of the block 2". It is pretty ridged and didn't sag. Some builders think Hardibacker is a waste of money but I found it about the same price as new 3/4" plywood from Home Depot, and I didn't have to remove it when the concrete cured. Put a temporary support at the front though. You will want to use ridged board around the perimeter such as 3/4" plywood or 2" x 6" that won't bow at the middle. You can even use a cross brace over the top to keep the sides straight but it might not be necessary if you decide to use 2" x 6".

Also, Have you considered adding some insulation under the grill hearth? You wouldn't need as much as for the oven. A thermal break between the fire (bricks) and the slab will increase performance.

Nice work so far.

Cheers,

[Mike D]

Re: Round shape

Thanks azpizzanut-

Did you use 1/2" or 1/4" Hardibacker? Yes I was thinking of putting a vermiculite/concrete insulation on the grill.

Mike

[azpizzanut]

Re: Round shape

Hi Mike D,

It measures .420". I bought it in 3' x 5' sheets. Use a carbide cutter (then snap like drywall board) or a carbide tipped saw blade. Wear a face mask. It is much harder than drywall but will crack where you don't want it to if handled roughly. There is good information on-line so you can read about it. James Hardie: HardieBacker 500 backerboard | Residential Siding from James Hardie

Cheers,

[Mike D]

Re: Round shape

Is it possible to over rebar the hearth? I was thinking about using 3/8 " rebar and putting it in every cell, too much? I would go up and over each side (a big u shape) and tie it all together. -This would put the rebar on a 8" spacing. The plans call for 1/2" with 12" spacing.

-What do you guys think? I would much rather over build it than worry about it falling apart.

Mike

[brickie in oz]

Re: Round shape

Did they use re-bar in ancient Italy? No, are the ovens still there, yes..