It was a cold and misty day when we laid down stamped colored concrete over this outdoor patio in Arlington, Texas. We used a stamp to create both a stone-like texture and a Verona stone pattern. Had it been summer, this project would have been impossible; the heat would have dried the concrete overlay material too quickly to apply the stamped pattern. Since it was cool, we were able to wrap it up and set up "Do Not Cross" tape around the area and left. Imagine our surprise when we returned the next day only to find that someone had ignored the tape, walked straight through the stamped colored concrete, and left behind their footprints. We were lucky because, though the overlay material was still a little soft, it had hardened enough that the footprints were only just visible. It took some time and artistic liberties to blend them in but we got them out. Thankfully, our pedestrian saboteur did not return during our repairs or a few choice words may have been said.
Part of the repair process had us applying a water based stain whose color is easier to control. Since we were trying to blend it with the rest of the stamped colored concrete we wanted something that gives us a lot of control. Typically we have three different methods for tinting a stamped colored concrete project, all of which can produce different results.
The first coloring method involves mixing pigments directly into the concrete overlay mixture before it is poured. This method creates a fairly uniform color throughout the concrete layer. Normally, the overlay material is an off-white; depending on how much pigment we mix into it we can create medium to darker hues of different colors.
The second way to tint stamped colored concrete involves a using a material called release. Before applying a stamp, we apply either a colored powder release or clear liquid release across the concrete surface. Release prevents the concrete overlay material from sticking to the rubber stamps when we pull them back up after transferring the texture into it. Powder release is available in a variety of shades that mimic colors found in nature. The stamping process pushes the powder into the overlay, and 1-2 days after the overlay hardens, we use a power washer to remove most of the release. What gets left behind contrasts with the base color of the stamped colored concrete, creating variegation and multi hue shading throughout. In our Arlington project we went this route and produced a brown-and-tan effect. The coloration is darker where the powder was pushed into the concrete surface by the stamps.
We don't use powder release on indoor projects, since the powder would leave permanent stains on carpets, walls, everything. Even for outdoor projects, powder release can be messy, and cleanup takes time as we have to get rid of all the powder. We're big fans of clear liquid release as it evaporates and doesn't cause a mess, but it doesn't color the concrete, either which leads us to our last method of applying color to stamped colored concrete. These happen near the end of the process; after the concrete overlay material has hardened. Our two options are either a water-based stain or an acid stain.
Water-based stains can be translucent or opaque. Pigments are sprayed over the concrete overlay and fill the pores tinting it the desired color from below the surface. This process can create rich, multi-hued color variations. A wide range of colors are available, and the pigments can be mixed together to create new colors. Also available are translucent acid stains that create enhanced variegated effects including wide color variations, mottling effects, and marbleized appearances. Acid stains contain metallic ions. When the acid is applied to the concrete, the metallic ions produce a chemical reaction with the free alkaline in the stamped colored concrete, which forms oxides that produce a color. Different ions produce different colors. Iron ions, for example, produce oxides that create browns, tans, reds, and blacks. Copper ions, meanwhile, result in blue and green colors. It's impossible to predict how the acid will react with the concrete; effects can vary widely, even in the same area. No two surfaces covered in an acid stain will be exactly alike all we can generally do is control how dark it gets. Ultimately for this stamped colored concrete project in Arlington, we went with a powdered release as they were looking for more subtle color variation and the area was perfect for it. In the end the owner was pleased with the result.