How to deal with sloppy slab when pouring sidewalk adjacent

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icrusbound

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Hi, and thanks in advance.

I am pouring a 6' x 60' side yard next to the slab. I am in San Diego where I have not seen it really freeze since I showed up here 35 years ago. There was previously a brick path there with about 8" of concrete next to the slab that transitioned into the brick. It seems in my research that there is a bit of a camp split between the expansion joint evangelists and the tie-in die hards. I am inclined to have an expansion joint and let the new concrete move independently of the existing slab. However, after laying the forms and digging up the earth, I have discovered that there are large amounts of slab slop (my newly coined term that you have to pay a 75 cent royalty to use) that extends into my form area just below the surface of the earth, such that I would have to cut and chip about 2 inches deep by somewhere between a few inches to a foot wide to 60 feet long to get a 4" smooth vertical surface to have an expansion joint. The alternative is to use this concrete to attach to and drill rebar through into the existing slab to attach my new walkway to. The walkway will not bear heavy traffic, it will be welded steel mesh reinforced, and I have a drop of about 1.25" for the 6 foot width.

So, my question is, what is the best way to proceed? It would likely take me a few days to cut all of the offending concrete away were I to decide on the expansion joint route. Raising the forms above the problem area is not an option. Are there any options I have missed? If I fix the new walkway to the slab and things go sideways, am I risking my new slab only or possibly my existing foundation (which appears to have a footing about a foot deep)

Any input is appreciated.

Thanks,

Anthony.
 

Terry

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I like the idea of drilling into the old to insert some rebar to keep the new concrete at the same level.

EDIT
I reread the part about the slop and yes, that should be cut off. I glossed over the part that it was at ground level. That won't work.


Concrete will shrink and crack half way betwen the longest runs. My concrete guys will groove the concrete into sections to create a thinner (weaker) point that allows the crack to occur where it isn't noticeable.
 
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icrusbound

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Thanks for the responses guys. One more quick question: Can I get close enough to the slab to cut flush with it if I have a concrete saw? I'd be happy to rent one.

BTW, I realized after posting that the previous owner that laid the bricks did so at a very low level (which is why that side of my house has a 1' vertical wall of slab showing. Which, subsequently, is where I had the concrete pad for my AC laid. The AC is the main reason I can't raise the pad to a new level. If the new pad were 4" higher the ac would be on a 3' square pad sitting 4" lower, essentially creating a bowl for water to sit in. Wish I had realized that when the AC went in.

Thanks again,

Anthony.
 

icrusbound

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So, just in case anyone else reads this, the saw rental was not really an option. They are all too big and have too much guard or shaft on either side of the blade to get close to the wall. Plus, not sure if I'm just late to the game, but the BORG requires that you purchase a saw blade to go in the saw you are renting. The blade is actually more expensive than the saw rental. So, poop on that. I purchased a 7.5" makita blade for my circular. The one with diamond bits and gaps all the way around (sort of making teeth). It cost $27 I think. I then disassembled my circular to remove the base plate, guard, etc. And, voila, master concrete cutting tool. Still can't get quite flush, but close. I found the easiest way was to cut down in at a slight angle inward toward the wall, and then undercut horizontally. Then, with some pretty serious whacks with a sledge and a chisel, worked the pieces off. Rather than removing the whole chunk, I just cut out a shelf of sorts just below the dirt line. BTW, I burned through a 4.5" makita blade of the same kind fairly quickly, but the 7.5" one was quite resilient.
 
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