Even when a concrete floor is in good condition, there may be other reasons to cover it up with a new concrete overlay. Decorative stamped concrete is an excellent way of transforming a drab or problematic concrete floor into something beautiful. This home in Trophy Club, Texas had an exposed aggregate finish on both its front and back patios. They were in good condition, but the homeowner was ready to kiss them goodbye and start over for reasons we'll discuss below, so he contracted us to lay down a stamped patio finish instead.
Exposed aggregate floors have small stones partially sticking out of the concrete. The stones (also called aggregate) are typically small, smooth, with varied colors. The most common aggregate floors tend to use pea gravel stones that are about 3/8" in diameter, while more expensive surfaces may use specially colored stones that are smaller or larger. Exposed aggregate has been available as a decorative element for concrete floors for decades; it is relatively economical and has a distinctive look. It tends to be somewhat non-slick, making it a good choice for outdoor surfaces like sidewalks and pool decks. Unfortunately many of these pros are also its cons – since it has been around for so long, it can sometimes give an area a dated look and if the stones stick out too much from the surface, it can hurt to walk on it with bare feet.
We often get calls from clients who are trying to dress up their exposed aggregate patios. We can do this by using an overlay to create a stamped patio but only if the original floor is in good condition. If the small stones are popping loose all over then it may not be a candidate for the overlay process. A good way to test this is by using a power washer; if just a few of the aggregate stones are blasted off by power washing then we can proceed. If a lot of them are coming up, the concrete itself may be too deteriorated for an overlay.
Many of our clients want to cover exposed aggregate floors with something beautiful and easier on their feet, like a skim coat or a stamped overlay. Our homeowners wanted to be able to walk barefoot over their patios and have them look good at the same time; a stamped patio overlay was the best option. Though a skim coat by itself can cover the stones, you can sometimes still see a little bit of the texture of the exposed aggregate coming through. It's not a bad look but in this case our homeowners wanted to completely eliminate it so the stamped overlay, being thicker, completely buries all the stones and creates a smoother, softer surface.
Our client had two patios, one in the front and the other in the back; each one was to receive the stamped patio overlay treatment. We started by grinding the surface to roughen it up for the first overlay coat which is a skim or bond coat. A skim coat overlay mixture is fairly watery and can easily fill the pores and spaces between the aggregate particles, creating a nice, new concrete surface for the stamped overlay to bond to. Once it had hardened we followed up with a second skim coat over which we immediately applied the stamped overlay. Why another skim coat layer? While the skim coat is watery, the stamped overlay is much stiffer and drier. If we just slapped it on to the first coat without that watery second skim coat in between it wouldn't stick as well. That second skim coat wicks into the first one and just as easily into the drier stamped overlay material on top of it "gluing" everything together once it dries.
The surface of the existing concrete layer can affect the price of a stamped patio project. When the existing concrete is exposed aggregate, we need more concrete to adequately cover the aggregate particles. A stamped concrete layer poured over flat, bare concrete would require less overlay material. 50 pounds of a stamped concrete mixture poured over flat, bare concrete can cover on area between 20 and 22 square feet. 50 pounds of the same overlay mixture poured over exposed aggregate can cover an area between 15 and 17 square feet.
After pouring it all out, we applied a stone-like texture and scored a checker pattern into the front and back stamped patio. For the front stamped patio, we colored some of the square tiles brown to make them stand out while leaving the base a neutral gray. The result was far more appealing than the exposed aggregate. The homeowner was happy with the result, which she found was a lot easier to walk across without hurting her feet.