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Bad Concrete Cannot Be Fixed with an Overlay

By Chris Sullivan – ChemSystems, Inc.

Question:

Our condominium board plans to have a decorative concrete overlay applied to our 35- year-old concrete walkways, which have existing cracks and many unlevel areas. That concerns some of us. The board members want to apply a 1/8- to 3/8-inch overlay, but that doesn't seem to be thick enough. Please advise. Our location is right on the Gulf of Mexico, so the walks are exposed to a coastal environment.

Answer:

I am not worried about the environment – decorative concrete overlays can handle Gulf Coast conditions. However, the minimum thickness of the overlay should be ¼ inch. Because overlay materials are polymer modified, they are designed to go down thin and still maintain strength.

I am more concerned about the cracks and uneven areas in the existing walkways. Overlays are only as good as the subbase they are applied to. They are not intended to fix poor concrete, but instead are meant to give a new aesthetic look to concrete that's in good shape. Put these overlays on cracked concrete, and you will get a cracked overlay. (See When to Use a Polymer Overlay.)

Another bit of advice: If your board is looking at an overlay for cost savings, they are going down the wrong road. A stampable overlay applied by a reputable installer will cost about as much as new stamped concrete. The reason to use an overlay is if the concrete in place is in good shape and or it is located in an area that's not easy to access, resulting in damage to other structures or surrounding landscaping during the removal process.The concrete walkways you describe do not sound like good candidates for an overlay. Their life span of 35 years is a good one, and it might be best to start over.

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