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RobertE 04-12-2008 07:01 PM

Old Garage Slab Repair
Scenario: 1930's garage. 18.5 x 20. Very inconsistent unreinforced slab floor, varying from 1" to 4", sort of cement veneer over very poor, crumbling, larger round rock/cement mix, over wet clay. 6" stem on 2 sides. I've removed a section in the middle, 6.5 x 15, with the expectation of making it 10 x 15 and strong enough for a car. Code requirement is "replacement in kind" for This Olde Garage repair. Next, I'll epoxy coat it.

The question: How thick? What kind of rebar? Underlayment and vapor barrier?

Hint: I generally overbuild my own stuff.

Grateful for any and all advice.


glennjanie 04-13-2008 07:07 PM

Welcome Robert E:
I would make it 4" thick with #4 re-bars on 1' centers both ways and spaced to the center of the slab. The slab also should be on top of at least 4" rock for drainage and a 6mil polyethylene plastic vapor barrier.

RobertE 04-14-2008 04:11 PM

Thanks, Glenn

I'm on it!


RobertE 04-25-2008 07:20 PM

So, today we poured the slab on the 10x15 area I removed from the original floor. 1/2" rebar, 12" centers, 4.5-5.0 thick 3000 psi over a compacted bed of 3/8 gravel 4" deep. I think we did okay for a Nissan Sentra. Waiting 30 days to slow cure, then an epoxy coating and start on storage cabinets for all the stuff. Meanwhile, a 2.5' parapet from the existing garage.

I love my job!


inspectorD 04-26-2008 04:45 AM

Great job
Thanks for sharing Bob...hope you get many years of enjoyment out of that hard earned piece of rock.:)
Fun isn't it.:D

RobertE 05-02-2008 02:39 PM

I'm adding a shed type addition to the back of the garage, making the back wall load bearing. In excavating the footing to add the 10x18.5 slab, I've found that there is no real footing under the original slab and 6" stem wall. Is it possible to dig out a suitable space under the existing slab? Or, is it more sensible to cut off 8" of floor/stem wall all the way across and replace the whole thing while it is still non-loadbearing. My permit is for the addition only, while repairs the the existing slab without permit would be "in kind". So, I don't think I can pour the footing for the new slab under an excavated old section at one time. It would have to be done separately to avoid the cost and time of a plan change.

inspectorD 05-02-2008 05:41 PM

You better tear down the whole foundation and slab and start fresh.:rolleyes:
I'm just kiddin, you don't need that for San Diego:D
It is a constant 70 degrees out there. Your part of the country is usually only a slab on grade anyway. Exept for an occasional varmint gettin under there, I wouldn't worry to much.

If your concerned check with your local building official for more specifics for your area. They will be the ones to tell you what you can get by with anyway. :) You guys are sooooo lucky.

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