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Q.What is the best way to tie the new slab floor of an addition to an existing slab-on-grade foundation?

A.The best way to tie in a new slab is to drill into the edge of the existing slab at least four inches, and grout in short lengths of rebar, which will extend into the new slab. This will prevent differential movement between the slabs. If there is a vertical wall extending down to a footing under the slab edge, the edge of the new slab should extend down to the old footing, as well.