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
- 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
- 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