Demonstrations seen on a trade-show floor make stamped-concrete installation look like a snap — just color, stamp and seal. But veterans say otherwise.
After all, you’re transforming simple gray concrete into brick, flagstone or cobblestone. The coloring and stamping require care. Then there’s the “hand-tooling” that’s needed to texture the edges and tight spots where a stamp won’t fit. Timing becomes even more important because you must complete the stamping before the concrete sets.
Mastering stamped concrete takes time and attention to detail. Here, we take you through the process.
STAGE ONE: ADDING COLOR
Installers most commonly color the concrete with one of two methods: “integral color” or “color hardeners.” Each has its own benefits and drawbacks.
• Integral color means that the concrete comes from the batch plant already tinted. The slab will be colored throughout its entire thickness. Because crews don’t have to worry about adding color, this option may work best for beginners or small teams that want to concentrate on learning to texture the concrete. This product comes in fewer colors, partly because it can’t be tinted lighter than the concrete’s original gray.
• Color hardeners are applied and then troweled into the slab’s top couple of inches during concrete placement. They’re called color hardeners because they increase the concrete’s surface strength to 7,000 to 8,000 psi of impact resistance, says Clark Branum, director of technical services at Brickform Products in Rancho Cucamonga, Calif. Color hardeners provide a greater selection of hues and can produce lighter shades, including white. This product adds an extra step, however, so beginners or smaller crews may want to avoid it — or at least train with color hardeners on smaller projects.
Follow these guidelines during the coloring phase:
Watch the mix as it comes from the plant. Make sure that proper consistency and color are maintained from batch to batch.
Avoid adding water. Wetting an integral color mix might change the shade. If you need to slow down the set, consider using plasticizers and water reducers, Branum says.
Protect all adjoining areas. The powder that creates the color is broadcast by hand and will scatter. Upon contact with moisture, it will become active and color any surface upon which it lands, making it difficult to clean.
Distribute evenly. Be sure to apply the powder with a consistent level of thickness to prevent uneven coloration.
Manufacturers typically recommend one 60-pound pail per 100 square feet (or 0.6 pounds per square foot) for standard colors. Lighter colors may require more. To help ensure even application, divide the deck into 100-square-foot sections. Place a 60-pound pail in each area, so you know how far each bucket must go, recommends Bob Harris, president/owner of the Decorative Concrete Institute in Douglasville, Ga.
Saturation. Color hardener is a powder, so it can become cakey if there’s not enough surface moisture to saturate it. This can cause dry spots, which makes the powder difficult to work in and, in some cases, could cause delamination down the road.
One clue to finding the proper amount of water lies in air entrainment. Too much air means not enough water, Branum says. Ideal air entrainment depends on regional conditions, but it usually falls between 3 percent to 5 percent. Anything above 6 percent is probably too high.
Apply the powder in two stages, beginning with the first 60 percent. Wait for it to absorb the moisture from the concrete. This can take five to 10 minutes, depending on heat and humidity. (Don’t wait too long or the powder will begin to dry and form a crust.) Then float the powder in. Finally, go through the same process with the remaining 40 percent of the color hardener.
STAGE TWO: RELEASES
Once the concrete has been poured, colored and troweled, it must be prepared for stamping. This requires a release agent — a substance that prevents the texturing tools from sticking to the mix. Release agents come in liquid form or a powder called color releases.
Color releases not only help separate the concrete and tools, but they can also add extra tint, resulting in an antiquing effect. The added layer of color becomes embedded into the joints, fissures, veins and crevices left by the stamps to enhance the texture.
Powder releases are scattered over the top of the freshly troweled slab. It’s a little messier than the liquid form because residual must be washed off two to three days after stamping.
Liquid releases are cleaner; however, they are not tinted. Some installers will compensate for this by adding a little powder color release to the liquid release.
When working with release agents, keep these tips in mind:
Apply the right amount of color release. Without enough, the texturing tool may stick to the concrete and leave a grainy look. Too thick a layer will prevent the concrete from receiving the stamp’s full impression, resulting in a shallow texture, and/or spots with no texture at all. “They can end up texturing the release and not the concrete,” Branum says.
As a general rule, disburse evenly at a rate of 3 to 4 pounds per 100 square feet of concrete, Harris says. At that rate, a 5-gallon pail will cover approximately 1,000 square feet.
Precondition the stamping pad. To ensure that the stamp will lift easily off the concrete, brush a layer of the powder or liquid release onto the bottom of the mats.
Combine releases for extra color depth. Combining colors can make the surface look more authentic. This is done by using an integral color with a couple of color hardeners and two or three color releases. If a client wants the look of a specific stone, carefully examine a sample of it for color, then choose your various tints appropriately. It’s best to stay within the same family of hues, advises Rick Wild, owner of Creative Concrete, LLC, an installation company in Perrineville, N.J.
STAGE THREE: THE IMPRESSION
Once the slab is prepared, it’s time to begin texturing the concrete. The rigid rubber stamps generally come in two varieties: a patterned type made to look like brick or stone, or continuous texture, which features background veins, fissures and other irregularities. The stamps are placed on the concrete, and installers walk on them or pound them with tamping tools to make sure they go in deep enough. Then each stamp is lifted and repositioned next to the last one that was put down. It’s like an intricately choreographed game of leapfrog.
When texturing the concrete, consider these suggestions from veteran installers:
Don’t skimp. Have enough stamping tools on hand to span the complete width of the area to be stamped, plus two. Without enough stamps, you can’t move fast enough and the concrete will dry. In addition, the stamps are used to secure each other while installers walk or pound on them. Otherwise, the tool can slip.
Watch the timing. Before stamping, make sure there is no standing water. Then ascertain that the concrete is plastic enough to support the installer. “If [the concrete] is too soft, installers will fall right through and make holes in it,” Branum says. On the other hand, if it’s set too much, you won’t be able to make enough of an impression.
Check the set with your thumb: It should leave a mark, yet there also should be resistance from the concrete below, Branum says.
The timing will vary slightly from stamp to stamp. When creating a shallower texture, such as some wooden plank varieties, allow the concrete to set a little longer. When using deeper patterns, such as flagstone, the concrete should be a little softer.
Set the stamping tools square to each other and “randomly.” The stamps should interlock, with no gaps in between. And don’t put the same tools next to each other. You want the surface to be randomly patterned, like a true stone or brick deck. Manufacturers have made this easy, either numbering or labeling the stamps so you know which are alike.
Be careful on a drastic slope. The stamps will want to slide down, breaking the interlock, Harris says. Start placing tools from the lowest elevation, working up the slope. That way, each will have another below it for security.
Lift the stamp quickly and precisely. Generally, the stamps should be lifted within five minutes, Branum says. If they sit too long, water from the concrete can begin to form condensation.
Remember: When lifting the stamp, the concrete is still impressionable, so pull the tools up carefully. Use both handles, and lift them at the same time. “Sometimes guys will grab one handle and lift the tool, and the bottom edge of the tool will kick out and tear the surface,” Branum says.
Hand-tool the edges. The stamps won’t end neatly where you want — at the edge of the slab or where it meets a vertical structure such as the home or a pillar. You can’t just jam the stamp to fit in the tight spaces created by the deck forms or the wall. This is when you must do things by hand. First, go over the unstamped area with a texturing skin. This flexible mat is stamped with the background texture that you’re using. This ensures that the whole area is impressed with the texture. Next, take a flexible stamp mat with the same pattern as the rigid tools. Bend it to fit the space and stamp as much of the area as you can. The mat can’t completely fold, though, so it’s not going to reach the last inch or two at the very edge. That’s where you must manually finish the “joints.” Harris likes to use random-sized hand chisels, and line them up with the joints left from the stamp to continue the lines from the pattern.