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Discussion Starter #1 (Edited)
Hello,

What would cause a relatively newly poured concrete slab to raise adjacent to pre-existing concrete?

I have a garage extension where a section of the old concrete slab was removed (along cut lines), a wall moved, and then about 1000 square feet of concrete was added within the confines of the foundation. Four months later, I am seeing that it has unevenly raised against the old concrete as high as 1/8 of an inch. Since I eventually plan to epoxy coat the floor, this is a huge concern.

Sinking I might understand if the bedding wasn't done properly, but raising? The only culprits that I can think of is either cold weather freezing/thawing and/or water soaking through the soil from the other side of a four foot high retaining wall that is apart of the structure.

The job was done by a local professional company with a great reputation. I am just getting a little intel before I call them back out.


Peace,
Dr. Z.
 

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Clay is a known issue with expanding and contracting due to moisture. But the answer is, whatever is down there is different fro what is under the existing concrete. Very difficult to judge when installing and I see no way to change it now. Since it is only 1/8th of an inch you might consider grinding down a bit to taper it from old to new.

Only problem with grinding is it may settle back to where it started as conditions change. Fun. Did they install rebar between the old and new? Sounds like they didn't and that might have held them together.

Bud
 

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As Bud mentioned there should have been dowels between the old and the new to lock the 2 sections together. If there wasn't there's really nothing to keep the 2 sections in alignment. 1/8" isn't an awful lot and you're going to have a hard time going back in a contractor for something that small. That much deviation is well within the normal tolerances for concrete work.
 

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If it happend relatively soon after the floor was instaled, my first guess would be "curling" of the concrete. It's not a very common phenomenon on smaller floors, but if you search the web for "concrete curling", you'll find plenty of info. In short, it comes from a differential in the concrete curing, causing the concrete to actually "warp" or "bend".......
 
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