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At a recent stamped concrete class in October, at the Decorative Concrete Institute in Georgia, I was reminded of the importance of having an understanding of different mix designs as the seasons change.

It was a tremendous learning experience for the students as the temperatures fluctuated as much as 35 degrees from day to day. Concrete isn't a generic product that is exactly the same every time you order it. There will always be variations, however slight. Sometimes those variations are intentional so you can tailor the concrete to meet the specific project requirements. Most professional stamp contractors have several mixes they like to use under different circumstances, often based on weather conditions and the size of the project. They may have a summer mix and a winter mix or even a floor mix for interior jobs.

Just because a certain mix works well for a contractor in certain regions of the country is no insurance that the same mix will produce the results you need in your environment. The best mix is the one that works in your area for your purposes and gives you predictable results.

The first day of the seminar, our first 4-yd. pour was at 9:30 a.m. The temperature was approximately 38 degrees F. I ordered a mix that consisted of a 2-percent non-calcium based accelerating admixture (NCA). A dry shake color hardener was used with the first chosen color covering the entire surface with 100-percent coverage, and then a contrasting color hardener used as an accent color. We finished the final stamping and touch-up at approximately 12:30 p.m., roughly three hours later. Our next 4-yd. load was the same day and the same mix poured at 1 p.m., but only consisted of 1-percent NCA. The temperature was approximately 60 degrees F at the time of placement. We completed our stamping and final detailing by 3 p.m., but the mix had less accelerator in it. The students were amazed by the effects ambient temperature had on the setting time of the concrete and ultimately the time to stamp the pad.

The second day consisted of pouring and stamping an 8-yd. pad. We poured the concrete at 9 a.m. with temperatures approximately 55 degrees F at the time of placement. This was the same mix design as the previous day's concrete, but because of the temperature and area to be stamped, we did not order any NCA in the mix. This area never received direct sunlight because of an overhead awning, and we were finished stamping and detailing at 12:30 p.m. with temperatures exceeding 65 degrees F. Our next 4-yd. pour was at 1 p.m. in direct sunlight with a temperature of almost 70 degrees F. As a test, we included 1-percent NCA to evaluate the setting characteristics. After using 100-percent color hardener in a multitude of colors as our coloring method, we used liquid release and seamless texture skins. We finished in just under two hours.