Many of the problems with stamped slabs result from ignoring the basics of concrete installation. Observe standards set forth by the American Concrete Institute and local requirements. Be sure to:
- Perform adequate surface preparation. Every slab needs some kind of sub-base that lets water through, such as sand or crushed stone, says Clark Branum, director of technical services at Brickform Products in Rancho Cucamonga, Calif. Make the bed level to ensure that the deck has a consistent thickness. If the concrete is uneven, it will hydrate at different rates, causing stress that can result in cracking.
- Don’t place the concrete until all standing water is gone. Extra water will affect how the concrete sets. The ACI frowns upon pre-wetting the surface. If you insist, Branum says, do it the day before so that the water can seep well into the surface.
- Allow the proper thickness and support. The deck should be at least 4 inches thick — 6 inches if extra reinforcement is needed. While many installers use wire mesh, steel rebar may be necessary if ground movement is expected.
- Add proper control joints. Place joints where they will best control the cracking. Don’t try to tailor them to the texture.
- Do not immediately seal the deck. Branum estimates that 80 percent of customer complaints result from installers who seal the stamped concrete too soon. The concrete needs to hydrate, and to do that, water must be able to escape. Sealing the material too soon traps water inside. Salts come to the surface, resulting in efflorescence. “The calcium hydroxide is white no matter what color the concrete is,” Branum says. “As soon as you add a brown, buff, tan or green, [the efflorescence] shows up in a big way.” The concrete should cure at least 14 days, but his company recommends waiting 28 days before sealing.