Stamp concrete

How to stamp concrete ?

1. Apply fresh concrete

2. Apply color hardener

After the concrete reaches the right stage of plasticity (generally when no bleedwater is on the surface), broadcast the color hardener by throwing it onto the surface from waist level or a bit lower to minimize the amount of material that drifts into the air. Work from the middle of the slab and back toward the edge forms to avoid a heavy buildup of color hardener on the edges. After the first shake of color hardener has been applied to the surface, give it five to 10 minutes to absorb water from the concrete and then float it into the surface. Right after bull floating the first application of color hardener, follow the same steps and apply a second layer of hardener to ensure complete coverage.

3. Apply release agent

Powdered or liquid release agents serve two important purposes : They impart subtle color contrast while acting as a bond breaker to prevent the stamping mats or skins from sticking to the concrete and disturbing the imprint texture.

The best way to apply a powdered release is with a dry tampico brush about 8 inches wide. Dip the brush into the pail of release and fluff it to load the bristles and coat them evenly. Then take the brush by the handle, holding it below belt level, and use your wrist to flick the release onto the surface in a light, uniform layer.

To apply a liquid release agent, use a pump-type sprayer to apply the release in a uniform layer onto the surface of the concrete right before you stamp. If you plan to use a tinted liquid release agent, add the tint a day or two beforehand if possible. This will allow the pigment particles to fully dissolve.

4. Stamp

Before you begin stamping, check to see that the concrete has reached the right stage of plasticity. If you begin stamping too soon, the concrete won't be firm enough to support the weight of workers or hold a well-defined imprint. If you start stamping too late, not only will stamping require more effort, you'll produce little or no texture with the stamps, especially as you reach the end of the job. Press your fingers into the concrete surface at several locations on the slab. If you leave a clean imprint about 3/16 to 1/4 inch deep, you can generally begin stamping. Another test is to place a stamp on the concrete and step on it. The stamp should hold your weight and not slide around or sink too deeply into the surface.

Pretexture along the perimeter edges of the slab about 6 to 12 inches inward with a texturing skin or flex mat. This step is important because when you're working with a nonflexible stamp, the tool will overlap the edge of the form and you won't be able to fully depress it into the concrete surface. By pretexturing the perimeter first, you'll get the texture you need and the full color from the release.

Once the edges are pretextured, the crew can begin stamping the rest of the slab with the mat tools. Generally, you should stamp in the same sequence that you placed and finished the concrete. For example, if you started placing the concrete in the top left-hand corner of the slab and ended on the bottom right corner, this would be the preferred sequence to use for finishing and stamping operations, working row by row from the starting point to the end point.

If the concrete is at the ideal stage for stamping, you should be able to impress the stamps into the surface by simply walking on the tools, possibly followed by a light tamping. The stamping crew should complete the first row before moving on to the second one. Typically, one person will place the starter tools and stand on them while grabbing stamps from the first row and leapfrogging them into the next row. While this person is moving and advancing the tools, another person can do the tamping. Depending on the stamp pattern, a third person may be needed to detail the grout joints.

5. Seal the concrete

Once the slab has cured sufficiently, you should apply a finish coat of sealer. Most manufacturers recommend applying the sealer several weeks later, after a light surface cleaning. Be careful not to apply the sealer too heavily, which could trap moisture in the slab. One of the most effective techniques for applying sealer is to combine both spraying and rolling, especially when the stamped pattern has deep grout lines. Going back over the surface with a roller where necessary helps to distribute the sealer uniformly.