2 car detached garage slab floor, tree roots busted the concrete up.

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Concrete needs to be removed, tree roots dug out (we had the tree removed), new concrete poured.

My question is about the way the new concrete will form with the old concrete under the walls. Is there anything particularly special that needs to be done in order for the new concrete to adhere optimally to the old concrete?

Anything else I might need to know?

Oh, and this will be done by a contractor, I just like to know the correct requirements to make sure they are properly followed by the contractor. We'll be using the guy who did our drive and patio.

 

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One contractor I spoke with said he would use a concrete saw along the walls. But I wonder if the rough edges from using a jackhammer might make a stronger bond between old and new concrete?