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mensrea 09-26-2011 11:05 PM

About to break ground - a few questions... please help
 
Greetings from Boston, Massachusetts.

I have spent the last few months conducting research and just finished a 540 sq. foot stone patio and am now ready to break ground on my pizza oven.

My plan is to build out the 42" oven, but, I have some questions before I start.

Here is what I'm looking for some help on:

1) My plan is to excavate an area of 89"x102" and ~24" deep. Is this sufficient?

2) I intend on excavating 6 footings around the perimeter of the foundation(73"x86") down to 36". Does this make sense?

3) I am going to reinforce the slab with rebar, but, I am unclear as to how I 'tie in' the slab/footings with the vertical cinderblock walls. Can anyone please clarify this for me?

4) After back-filling, I am going to go with a slab of 6", make sense?

5) I have a GIANT pile of blue stonedust left-over from my patio project. Can I use this stone dust in lieue of gravel to back-fill?

Many thanks!

Mingy 09-28-2011 11:38 AM

Re: About to break ground - a few questions... please help
 
There seems to be a lot of anxiety about getting below the frost line. If you are building a structure on a slab which is not going to connect to another building, I do not see why this is necessary. I have an engineered slab building about 1000 square feet, and it goes up and down with the seasons no problem. If you put a slab on top of footings, unless there is free space between the slab and the ground, it'll get push up by frost in any event.


I live in near Toronto, which gets pretty cold. I excavated down below the topsoil (which is what matters). Most developments only have a few inched of topsoil. I have a farm, and on my fields, its 16". My yard has been landscaped so I only had to go down about 4". I put down a layer of geotextile, then used 3/4" crusher run (bits and pieces up to 3/4") which I compacted with a plate compacter. I went with a 5 1/2" slab so I could use 2x6 forms. I placed rebar under where the blocks would go (2 each about 6" apart) plus 6" mesh, all held about 1 1/2" from the bottom of the concrete, where it does the most good. I also treated plastic conduit for electrical before pouring. I marked where my blocks were going to be on the forms. After I poured the concrete for the slab, I while it was still wet, I pushed a 24" length of rebar into the slab so they would come through the holes in the blocks. When I stacked the blocks, I could then tie longer rebar into the ones sticking out of the slab.

Other things I did:
1) I dry stacked blocks but glued them with construction adhesive. Its cheap and it means the blocks would not move during the pourt.
2) The 3 1/2 angle to support the door is overkill. I used rebard and a couple blocks, which I filled with concrete. If I had to do it again, I would not even do that: the 'top slab' is self supporting, so, provided you put a couple rebar above the opening, and support the form and opening with a few concrete blocks until the concrete cures for a few days.

If you insist in using footings, what they do is they put a couple rebar into the footings and bend them like an upside down 'L'. Then they tie the horizontal part of the upside down L to the horizontal rebar on the slab.

Again - I don't think it is necessary to provide footings. Your oven with rise a little bit in the winter and settle back down in the summer. People don't put footings in sidewalks, do they?

aceves 09-28-2011 04:33 PM

Re: About to break ground - a few questions... please help
 
Hi mensrea,

I take it you're in the legal field with that name? I am too. Here are my 2 cents on some if your questions. I'll let others fill you in on the rest.

For a 42" oven in a square/rectangular foundation, 73x86 should be sufficient. The depth will depend on your frost line. Why are you excavating a 89x102 area? Are you building additional counter space?

You tie in the rebar from the slab to the cindeblock walls by placing long rebar in a vertical position, letting the slab dry with the rebar sticking out, and then placing your cinderblocks over the rebar and filling the cores of the cinderblocks (where there's rebar) with concrete.

And you'll be OK using the blue stone dust instead of gravel, as long as there are some good-sized blue stone (gravel-size) in there, are opposed all fine dust.

Post photos and we'll be able to assist you better as we'll know exactly what you are talking about.

Good luck!

aceves

Neil2 09-28-2011 08:35 PM

Re: About to break ground - a few questions... please help
 
I agree with Mingy and aceves. Either do footings (or piers) or a slab on grade - not both. Unless you have very unusual soil conditions, a 6 inch reinforced slab on grade is more than adequate, even in frost zone areas. The subrade - the granular layer under the slab on grade - should be well drained and need only be about 4 inches thick if the original ground underneath is firm.

If the material underneath may be susceptible to differential settlement, for example if part of the footprint is on original ground and part on looser fill, or on fill from the original house construction (which is generally not compacted), then I consider going with full depth footings. If in doubt, drive a length of rebar into the ground at various points to see if it is consistent.

One note about tying the slab to the block wall. The verticals should be part of the ends of some of the slab rebar bent 90 degrees up and supported during the slab pour. One rebar at each corner is sufficient but you can do it more often if you want. Most people find it easier for the verticals to extend 1 foot or so up from the slab and then extend this up with more rebar tied to these "stubs" after the slab has set.

When you get to the suspended slab on top of the wall, you then connect these verticals with 90 degree bend into the suspended slab rebar.

larrycooper 10-03-2011 05:33 AM

Re: About to break ground - a few questions... please help
 
Ive just gotten my forms in place and are ready for concrete. I rented a post hole digger and drilled a few footers - some went deep others hit rock. Putting invert L rebar in deep holes. I'm planning on building some wings on sides of oven for prep etc. My township is really anal about codes so I'm submitting plans and see if they want to do inspection before the pour. I'm in Pennsylvania so frost line is a concern. I also used 8" forms and am specifying concrete to have .45 water to cement ratio- stronger. I'll keep you posted

larrycooper 10-05-2011 06:26 PM

Re: About to break ground - a few questions... please help
 
I met with concrete company owner and he advised me not to tie the piers (footers) into the slab. Since I already drilled post holes he said fill the with concrete and cover them with roofing paper to allow the slab to move freely on top of it while still retaining it's load bearing qualities. I'm putting wings on sides of oven and he said not to tie them in (rebar and remesh) with the main slab. Structures should be completely independant of each other - they can butt up to each other with some latex like grout. Found out here in pennsylvania the type soil is a factor in determining how deep slab should be - lots of clay is more stable and less prone to frost damage. too much rain here - have to pour next week.

Neil2 10-05-2011 07:00 PM

Re: About to break ground - a few questions... please help
 
How is the weight of your oven transferred to the piers ? A sketch would be useful.

One option is to extend the piers up and tie them to the structural suspended slab and do away with the structural slab on grade (and walls) entirely.

larrycooper 10-06-2011 06:52 AM

Re: About to break ground - a few questions... please help
 
I just met with concrete company owner -been in business for a zillion years - he said not to tie in piers to slab - pour piers first - let cure - then cover with roofing paper to allow slab to move freely on top of piers. 8" slab reinforced with half inch rebar and remesh - thinks piers were overkill in Pennsylvania with our clay soil but since I got em - use em. Some holes were deep and others just a foot or so. I would have to have been a lot more precise with holes had I intended to use piers for supporting hearth. Pour on tuesday unless it pours again - !@#%&* rain!


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