Some Concrete Stamping Details

Like you, I see a lot of the same problems over and over with stamped concrete. A few simple basics can eliminate most of these problems and elevate the public and builder / owner per-ception of stamped concrete. Just the basics.

No. 1: If color control matters you must use color hardener rather than integral color. There is nothing wrong with using integrally colored concrete and we love to sell the color but color hardener has the benefits of producing more accurate color replication and a denser surface, much more resistant to marring and water penetration. Tests done with Absolute Color Hardeners in Osnabrueck Germany showed that there was virtually no water penetration through the Absolute Color Hardener when cured under controlled conditions for 7 days. Integrally colored concrete would not pretend such capability. The final color is more stable using color hardener than integral color because the color hardener consumes the byproducts of hydration (CaOH)for its own hydration whereas these byproducts remain on the surface of integrally colored concrete as a white salt that masks the color.
Additional advantages using color hardener are your ability to choose light and pastel colors not possible using integral colors and substantial savings for colors like blue or high intensity color because you are not paying for all the color hidden in the concrete matrix.

No. 2: Both powder and liquid release can give good antiquing definition but require some common sense to achieve uniformity. As most of you have experienced, uniform set (often very hard to control on a large job) due to shadows or shaded areas, wind, temperature, travel time and so forth, can make your life interesting very fast. A distinct difference between liquid release and powder release is you will impart significantly better detail to the concrete using antique powder release than using liquid release.

No. 3: In the Northwest USA almost all concrete is specified with air entrainment. Air entrainment can result in at least two considerable issues for the installer and; hence, the discriminating customer. First, there is a natural repelling action between the air entrained concrete and the color hardener. For one thing air entrained concrete holds onto the water. There is little or no bleed to make the concrete accept the dry powder cast on the surface unless the concrete has been fatally damaged by adding too much water at the jobsite. Second, there are electrical forces at work somewhat like the repelling of same charges in magnets. These are highly complex chemical phenomena and I won’t waste your time pretending I can adequately address them. The result can be a poorly bonded skin of color on the surface rather that a good marriage of the concrete matrix with the color hardener. The potential for serious spalls is obvious. You have seen them.

No. 4: When stamping with fixed edge texture mats, especially when the pattern is aggressive, you have all seen tears on the shoulder of the joints. This is unsightly and takes some tedious labor to repair. Left unrepaired it is damaging to the decorative concrete reputation everywhere. (Use Absolute Thin Overlay (OLT) or Absolute Concrete Overcoat (OC) to make prefect repairs.)

If you will go to the trouble to order your concrete with no air entrainment you will see almost 100% of these tears disappear. The reason is fairly simple. The dough-like or sponge-like character of air entrained concrete holds onto the rocks. When you stamp and the rock has to move, the concrete mix moves with it and tears. With no air entrainment the rock will move through the concrete matrix and the concrete will fill after it and you will have a perfect cosmetic joint. I know some of you find that hard to believe. Try it. You’ll like it.

Note 5: My opinion is that you can produce better work if you order concrete with no fly ash. Most engineers will not agree with me. Many installers will. It is more of a feel and a sense from experience than studying the research. Have you ever tried to drill an anchor hole in 50 year old concrete, before all the fly ash fuss? Enough said. You may like the greasy feel when you finish fly ash but it is more prone to leave sweat tracks in your stamp pattern than when there is no fly ash. The jury may still be out on this one. Talk to your peers. You guys (and gals) on the front lines have lots of good information to share. You are wisely saying to yourselves, “we are living in a freeze thaw zone.” Yes, you are, but once you apply Color Hardener, the air is gone from the surface. Also, if you seal the surface, you nullify the purpose of the air entrainment.

Now a note of caution: Don’t take it upon yourself to ignore the specification, thinking the customer will appreciate your effort to present a perfect job. You could end up owning the job instead of getting paid for the job. Also, don’t push real hard to get a spec changed. The engineer or architect will sometimes use that as an excuse to blame you for something else that becomes a job problem because you pushed for changes.

Good luck and good concreting. Byron