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Supercontinent 02-26-2012 08:02 PM

Pouring new concrete around existing slab on grade.
Hey everyone,

So here is the deal. I have a slab on grade between my house and garage. This is a 3 season room/breezeway. We have water coming in when it rains hard. It only comes in at the sill board/slab interface and only in one low corner. The slab is actually below grade. This is an old house. So I assume it settled over time. The floor is tiled. And is crack free. We want to renovate this room anyways. So the walls are coming down this spring. But the roof is staying. So my idea is to pour new concrete around the existing slab. But the new pour will be higher than the existing. I was thinking 6 inches above the existing should be good. For a total of 9 inches (depending on how thick the slab is). I would pin the new to the old every 12 inches with rebar. Epoxy the rebar into the old. Then rebuild the walls in their original locations.

The questions:
1. Does this sound like a good plan? Or Is there something better?
2. What product do I use for the new to old slab connection to make it waterproof?
3. Is there a epoxy specifically made for the rebar connection?
4. Absolutely any advice would be great. I really want to do this right the first time.

Thanks everyone!

illanrob 06-19-2012 11:20 AM

Rebar to hold 2nd slab
I am doing something similar to you project for 8' by 6' side porch in Florida built in 1985.

I am surprised that you had no replies so decided to write. Even if you have started/completed your Nebraska project.

My other home in Alabama built in 1965 has a 5' wide by 30' slab on the front porch with 4 14 foot wood columns with no footings and the slab has moved away from the house 1/2 inch in the +40 years. The house has brick veneer all around and its slab is 2.5 feet below grade. The front porch entry way described above does not look too bad. Slabs not properly attached will creep.

You mentioned rebar. I am thinking of using rebar in my 8' by 6' project. I am adding concrete over an 8' by 6' side porch portion of the main house slab (all one slab if I recall the photos from 1985) to level it with the rest of the house. The rebar should help hold the new +3" concrete slab that I'm poring. Thinking of drilling the existing slab, placing rebar 1 1/2" into the new slab. Have not seen photos of using rebar in this way, to hold a 2nd slab in place.

I would not think that epoxy on the rebar would be that important, maybe some wire to hold it from falling thru, since the new slab would get a grip on it.

Your added 6" is to be above grade. Why is waterproofing the old to new slabs important?

12" spacing for the rebar sounds conservative, maybe you can do with less. I was thinking 6 rebar spikes for my 50sqft slab

8' by 6' and 3" or 4" deep is 12 or 16 cuft. Have read that < 27cuft of concrete can be done by hand by one DIY.

Will send photo of my project space if someone writes back.

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