Stamped, Patterned® & Colored Concrete
Back in 1994, a neighbor of mine installed a new sidewalk. Soon after it was completed, my wife and I walked past it. As I approached the sidewalk from a distance, I thought that it was a flagstone walkway. However, upon closer inspection (on my hands and knees!), I determined that it was actually concrete!
The deep color and realistic texture and pattern had fooled me. The sidewalk was absolutely gorgeous. The concrete was actually multi-colored. There were various shades of medium to dark green. It was impressive to say the least.
How is it Done?
Stamped concrete is nothing new. As a child, I did it to a neighbor's retaining wall one day with a stick. Boy, did I get into trouble! Actually, stamped concrete has come a long way in the past 25 years. Close to 100 different patterns are available, as well as numerous color options. The process is not that difficult, however, professional results will not be obtained by a first time DIY'r.
Patterned® or stamped concrete is really no different than regular concrete. It simply has a different texture and/or color at the surface. You do all of the preparation, form work, etc. as you would ordinary concrete. Reinforcing steel, thickness requirements, etc. are also the same.
The ingredients, however, do vary. Regular concrete often contains stones that can be as large as 1 to 1 1/4 inch in diameter. These size stones do not work well with patterned, stamped concrete. The maximum size of the aggregate (stones) should not exceed 3/8 inch in diameter. Here in Cincinnati, we refer to this gravel as pea gravel.
The concrete that is poured must be a certain consistency. It cannot be too stiff. If so, it will be difficult, if not impossible to imprint the concrete. The moisture content and fluid nature of the concrete will vary depending upon the outdoor conditions.
The concrete is placed, screeded and bullfloated just like ordinary concrete. Often it may be troweled before the stamping process. However, do not trowel more than one time! You may bring too much bleed water to the surface.
Should you decide to color the concrete, the color is often added before the stamping process is started. Coloration can be achieved by ordering colored concrete (VERY expensive) or adding the color once the concrete has arrived. Color is added on site by shaking special dried pigments on top of the wet concrete. The pigments are then troweled into the concrete. These pigments can often penetrate 1/8 to 1/4 inch. This second method works well in most instances. However, if the concrete chips, uncolored concrete below will be exposed.
Concrete can also be stained after it is installed. However, different color results are very common. The stain can be absorbed differently because of finishing techniques and concrete characteristics. Concrete staining is an art!
Plenty of Help
Stamping concrete requires plenty of experienced help. You need to work fast to imprint the concrete.
The stamping patterns or pads are often walked on by the installer or tamped with a large wooden mallet. These patterns can be driven up to one inch deep into the plastic concrete mixture.
If stamping pads are used, they often need to be treated with a form release agent so the concrete does not adhere to each pad. This is necessary to prevent concrete from clogging the pattern. Thin plastic sheeting can also be spread over the concrete to prevent fouling of the pads.
If you go to this much trouble and expense to install patterned Concrete®, you surely do not want it to crack. Well guess what? Concrete shrinks and cracks as it dries! It is a known fact. You need to make sure that control joints are placed at intervals of 10 feet or less. These joints must penetrate a minimum of one-fourth the thickness of the slab. Saw cutting works well in stamped concrete.
I would also recommend the use of 1/2 inch steel reinforcing bars in the the concrete. These bars will prevent cracks from widening when they do develop. In addition, the steel bars prevent displacement between two adjacent pieces of concrete. Steel is very inexpensive and takes little time to install prior to the pour. Be sure your concrete has this steel.