On 7/9/2010 7:54 PM RicodJour spake thus:

On Jul 9, 10:25 pm, David Nebenzahl wrote:

On 7/9/2010 7:16 PM David Nebenzahl spake thus:

Here's what I *think* I should do:

1. Drill holes into the edge of the slab, using rotary hammer & SDS bit.
2. Epoxy rebar dowels into the holes, long enough to overlap at least 18"
or so. Bind the dowels together with wire. (How many dowels? spacing?)
3. Add wire mesh over rebar? (What type?)
4. Add new joists across the short (3') dimension of the hole, using
joist hangers, plus cleats at the edges. (The existing hole is
completely framed by joists.) Two new ones should do it, giving a
spacing of about 16".
5. Place plywood (1/2"? 3/4") on top of the joists and cleats.
6. Pour concrete into the hole. Finish top surface smooth to match
existing floor.

Before anyone pounces on me, the order above is obviously wrong. Correct
sequence would be 1-4-5-2-3-6.

I don't quite understand what's going on with the wood joists below
the slab. Are they full length and adequately supported at both
ends? Or is it just a sort of boxed frame at the hole?

No, they're fully supported. About a third of the slab above is over the
room below, supported by the joists (about 2x10 as I recall).

If the existing 4" slab can take a vehicle (how?), the trick would
seem to be patching the hole and keeping vehicles off of the patch.
If you can accomplish that, then I'd probably just pick up some metal
decking (you only need a smallish piece, so you could buy a damaged
sheet that couldn't otherwise be sold), cut it to fit tightly in the
hole, seal the edges/gaps with spray foam, and place the concrete.
http://www.metaldeck.com/floor_deck.htm

There are a number of advantages to this approach, not the least of
which is you'd use less concrete and the patch would be a lot lighter.

So you're saying the patch could be less than 4" thick with the metal
decking?

I'd bolt down some barriers/guides to make sure that a vehicle would
not drive on the patch.

Could do, although they (occupants) might not like that. Are you saying
I'm not going to be able to make a patch strong enough to drive over?


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