If you're interested in adding a stone-like texture to a concrete surface, then stamped overlays are one way of doing that. Stamped overlays are a form of decorative stamped concrete that can imitate the appearance and texture of stone such as granite, sandstone, and roman slate. Wood-like textures are also possible. Decorative stamped concrete can also cover up defects in an existing concrete surface and transform it into something new and unique, no matter if that surface is indoors or outdoors.
At this restaurant in uptown Dallas, we laid down decorative stamped concrete with a stone-like texture and pattern. It was a large job, requiring eight guys to complete all the steps of the overlay process. We covered up their entire patio, which began at the wall of the restaurant and ended on the street curb.
The process is most commonly called an "overlay" because it involves laying a thin layer of concrete over an existing concrete surface. The concrete surface can be horizontal or vertical. The process takes several steps. First, we thoroughly clean the existing concrete of any stains or debris. Then, if the overlay project is vertical, we apply a metal mesh lath against the existing concrete, it is this mesh that helps prevent the overlay material from just rolling down the face of the wall. Next, we apply the overlay, which is a special mixture that includes a glue designed to stick to the concrete surface. The overlay typically has a colored pigment mixed into it; the color used depends on the homeowner or business owner’s preference. Later on, a colored stain can also be applied on the finished overlay.
To ensure that our decorative stamped concrete overlay has the same thickness throughout, we use a tool called a gauge rake. This tool may look a bit like a window cleaning squeegee missing a rubber strip, but it's actually a steel blade connected to a handle. A small metal strip is attached to each edge of the blade create a gap between the blade and the concrete you set it on. The gauge rake is swept across the wet overlay material, spreading it out in a thin layer the same thickness as the gap beneath the gauge. We then use a trowel to smooth out the surface and remove any lines left from the gauge rake.
The next step is to spray a release agent across the overlay surface. Release prevents the wet concrete from sticking to the rubber mats we use to apply the stamp, in the same way that a light application of dry flour can stop dough from sticking to your fingers. Without the release agent, the rubber mats would lift up bits of the wet concrete overlay and ruin its appearance.
Finally, we are able to proceed to the stamping part of a decorative stamped concrete project. While the overlay is still soft, we use rubber mats to stamp a stone-like texture into the overlay. Then we wait for the concrete layer to harden before using a diamond blade to cut individual stone tiles, random stone, or other patterns.
We followed all of these steps at the restaurant in Dallas. Weather is always a concern when laying decorative stamped concrete outdoors, but this time, the weather didn't cause any problems, it was people. While the overlay was still soft, a car pulled up outside the restaurant and jumped the curb, leaving behind some ruts in it. Luckily, because it was still soft, we were able to pour more concrete overlay and reapply the stamp to the damaged spot. The repair blended seamlessly with the rest of the overlay. They hit is just when it was most vulnerable, a few hours later and it wouldn’t have mattered, it would have been been nice and hard.
In a situation like this one, it would have been easier to do the repair if we had used rubber mats with the stone-like texture but no patterns. In this case they did have a tile pattern already part of the stamp, that can make it harder to repair damage as you have to align everything correctly, kind of like a jigsaw puzzle. If the pieces don’t fit together right, then it doesn’t look good. That’s one reason we like to use seamless matts, i.e., they have stone texture but not a pattern. We can always add that later by scoring (cutting) it into the floor with a diamond blade.
A stamped overlay is the best option if you are trying to get that look but already have concrete laid down. Consider the alternative for a decorative stamped concrete look, hiring a contractor to tear out and dispose the existing concrete, then starting over from scratch, putting up a new form and pouring a lot of concrete down to their give it some texture, an expensive and time consuming process. Stamped overlays, however, are more economical, quicker to install, and look just as good. In the next project we will discuss the differences between these two options and the benefits of a stamped overlay.