Although the steps and landings shown here have little square footage, they will require more skilled help to stamp the horizontal and vertical impressions than a much larger placement.
Joe Nasvik Although the steps and landings shown here have little square footage, they will require more skilled help to stamp the horizontal and vertical impressions than a much larger placement.

Based on the sales of color and stamps, most manufacturers of these products will tell you that stamped concrete still represents the largest segment of the decorative concrete business. It's also one of the most difficult of the decorative products to install because there are more finishing steps to complete in a narrow time frame compared to plain concrete. There are also several installation conditions that affect the outcome: weather, pattern layout, determining the right amount of labor for a job, and using durable concrete mix designs that are well-suited for stamping concrete.

Weather conditions

Colored concrete that bleeds for very long, either before or after initial set, results in more efflorescence that causes whitish blemishes on colored, finished surfaces. The best way to avoid the condition is to be sure that initial set occurs approximately three hours or less from the time of batching. This can be achieved by adding accelerating admixtures to the concrete either at the ready-mix plant or in the ready-mix truck when it arrives onsite.

The look of stamped concrete is affected greatly by surface crusting. It happens when the surface of fresh concrete loses excessive amounts of water due to weather conditions. It also happens when the sun heats up colored concrete causing the surface of a slab to set before the bottom does. The result is a hard, crusty surface and concrete below that moves under the force of the stamp being impressed. The mushy, ill-defined impressions with little texture that result have numerous small cracks between pattern lines. The best solution is to check the weather beforehand so you can determine whether surface crusting conditions are present. Use an onsite weather meter to do this. Decide first on the advisability of placing concrete that day. If you do decide to proceed, employ methods to manage surface crusting.

Forming and pattern layout

If you are texturing the surface of a slab only, there are few significant issues involving layout and forming. Patterning, however, requires planning and forethought. You must consider how the lines of a pattern should relate to buildings and landscape. Long straight lines or regular bond lines in a pattern must occur in the right relationship to form lines. When a pattern moves around an obstruction, such as a planter, bringing the pattern back together requires careful planning and layout work.

Staffing a project

It would be nice if contractors could work out a formula for labor based on the square footage of a project. But every job has its own level of difficulty, so deciding on the right amount of labor is more difficult. Profits suffer when a job is overstaffed. But quality suffers when there isn't enough. Labor costs more when concrete can't be placed by the chute on the truck, when placements are long and narrow such as in a parkway, and when more handstamping and detailing is required.

Durable concrete mixes

Concrete mixes for floor construction using 1½-inch top-sized aggregates have great performance characteristics, but not for stamped concrete. Large aggregates don't permit very deep impressions and they dimple the surface. Impressions more than ½ inch deep work best when top aggregates are ½ inch or less because stamp blades can easily move the stones to the side. The problem with small aggregate mixes, however, is that more cement must be added to the mix to fill the increased number of voids between aggregates, which increases water demand, resulting in more shrinkage and cracking. Mixes also should be adjusted to manage seasonal weather changes to maintain the best impression quality. You should consult with your ready-mix supplier or someone who is expert in developing mix designs to help you with this.