You may be wondering how tough an overlay can be. It's a layer of concrete that can be as thin as a piece of paper or as thick as a brick, so it's understandable to be concerned about its overall strength and how much weight it can take. After all, if the homeowner in Denton had to repair his concrete patio after an intense hailstorm, is an overlay really strong enough to withstand the next storm? Well, rest assured that overlays can take a lot of damage. They can also handle a lot of weight, even several thousand pounds, and still look good after years of use. They're an ideal solution for any concrete surface, even driveways. It's possible to drive straight over an overlay without causing damage, so a stamped concrete driveway can be an option for your home or business.
We put this to the test at this Carrollton, Texas home, where we were contracted to lay down a stamped concrete driveway to cover up older, drab looking one. Sections of the driveway had been torn out and then re-poured by another contractor. The result was a patchwork of newer, whiter concrete mixed with an older, darker one. It was a complete eyesore, and the unhappy homeowner talked to us about transforming both sections of concrete into a stamped concrete driveway.
An overlay is a concrete mixture made up primarily of cement and sand. Most horizontal overlays, if they are going to be stamped, are between 1/4" and 1/2" thick; this may seem a bit thin, but the overlay is poured over a much thicker layer of concrete. When properly applied, the two layers bond together, strengthening both. Overlays have been made of various materials, but cement-based overlays have been in use for decades. Since the eighties, polymer resin has become a popular ingredient in cement-based overlays. By polymer, what we really mean is glue. It's this polymer (glue) mixed in with the cement and sand that allows for an overlay to be applied to concrete in a thin layer and not peel up the next day.
Different manufacturers use different polymer resins in their overlay mixtures; some use latex, while others use vinyl or acrylic blends. Both vinyl and acrylic offer greater UV protection and greater bond strength than other polymer resins. They help the overlay adhere more tightly to existing concrete layers, which is an important element of an effective overlay. Blends that primarily use latex have more flexibility than a pure acrylic or vinyl blend. The best overlay material is a hybrid mix, utilizing all of the above in carefully proportioned quantities to give the best results. Of course, these tend to cost more than the run of the mill stuff but we think it's worth it.
Polymer modified overlays can be applied in thick or thin layers without failing so long as the concrete it is being applied to is properly prepared. The polymer resin helps the overlay resist damage from salt, chemicals, exposure to UV radiation, intense weather conditions, and traffic, things that hammer on a stamped concrete driveway. Overlays in general help protect the original concrete from damage from the daily wear and tear. While regular concrete can take weeks to cure, overlays harden in a matter of hours and usually have a higher compressive strength than the concrete they go over. Case in point, we returned the next day and accidently backed our full size pickup (dually) across the overlay while turning around on the street. It's a big truck, clocks in at about 5,400 lbs. and that's with nothing in it. We were sweating bullets when we realized what we had done, I mean, we had just applied the stamped concrete driveway overlay the day before, but we jumped out, looked all over and saw…absolutely no damage, I mean, zero, nothing, nada. It held up great with no issues. That's one tough material. Please don't do this though, we do recommend waiting at least two days before driving on it as temperature affects how fast an overlay hardens, the warmer it is the faster it hardens and vice versa; had it been the middle of the winter we might have not been so lucky. In this particular case our homeowner chose a tannish-brown stain for the home's new stamped concrete driveway. Overlays can be stained or dyed a variety of colors. Next, we will discuss the benefits and disadvantages of light and dark colored overlays compared to regular concrete.