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Concrete over existing concrete

by Carole
(Oklahoma City, OK)

Q. My patio is lower than my yard which results in flooding. Two contractors have said they could raise my patio about 5" (1 inch of sand over the old, then 4" of new concrete). One contractor said they would lay 1" of sand over the old patio, place some sort of wire, then pour 4" of new concrete. He would also cut out the edges of my old patio about 4-6", which would be filled in completely to keep the sand in, etc. Have you ever heard of this? Is it feasable and will it work? It sounds legitimate since two contractors both said the same thing. I am getting ready to spend a lot of money so I just want to make sure the patio will last. I also haven't been able to find anything on-line to suggest this particular procedure works. Any help would be greatly appreciated.

A. This method does work and I have done it several times with no problem. You can pour new concrete over existing concrete as long as there is a buffer (sand) between the two slabs. The buffer allows the two slabs to move and shift separately from one another. Cutting out the edges is a good idea to keep the sand in place, but I always just make the new slab a little bigger and pour the edges deeper to prevent that.
Wire mesh will also help make it last longer. You should ask about adding fiber to the mix for additional reinforcement. It's relatively inexpensive, creates no extra work for the contractor, and has the advantage of being distributed evenly throughout the slab.