Have you ever been faced with the challenge of stamping concrete in cold weather? Maybe the temps have dropped a little sooner than expected or you might have that one last stamp job left for the year. Of course, we would all rather just wait for a better day or even until next spring. But, here in the real world, that's not always an option. Being based out of Ohio, we have had to deal with this issue at the beginning and end of every concrete season. Here are some tips that we have leaned over the years that might help you out.
1. Extra Cement
Just simply adding an extra 1/2 sack of cement can be a great way to get your concrete to set up faster without adding any accelerator. This would be our go-to move in early fall or late spring. So, if you want your concrete to set up a little faster, try ordering 6.5 sack instead of 6.
Accelerators are obviously the star of the show. Adding accelerator to your concrete will be the most effective thing you can do to speed things up. However, it is important to understand the different types of accelerators. The main two types are Calcium Chloride, and NCA (Non-Chloride Accelerator). Concrete dosed with Calcium Chloride will set faster than if it had been dosed with NCA. If you are just pouring standard (Gary) structural concrete, Calcium is a great choice. Decorative concrete on the other hand is a different story. Calcium Chloride is corrosive to steel reinforcement, increased efflorescence and tends to negatively affect the color of the concrete. So, when pouring stamped or any other kind of decorative concrete, the best recommendation is to stay away from Calcium Chloride. If you are new to NCA, the biggest thing to understand is the dosage. You will need roughly twice the dosage of NCA compared to Calcium. Example: you will need 2% NCA to gain the same effect as 1% Calcium.
3. Hot Water
Is you ready-mix plant running hot water? Hot water can go a long way in amplifying the effects of extra cement and accelerators. The time of year that ready mix plants start and stop running hot water will vary depending on what part of country you live in. Make sure to work with you local ready-mix supplier to stay in tune with what is happening at the plant.
4. Pour in the Morning
Pouring in the morning is good practice all year around. In the summer months we do this to avoid stamping in the heat of the day. In cold weather conditions morning pours are important because you will need extra time on the ground for concrete to set up enough that you can stamp it. Pouring at 2:00 in the afternoon on a cool day will likely result in stamping after dark. So, get your concrete poured in the morning, so you can stamp it in the daylight.
5. Pour at Lower Slump
Pouring at the right slump is important any time of the year. In cold weather make sure to adjust accordingly. Remember, we are trying to speed up the set time of our concrete so it will hold our weight and we can get it stamped. Pouring at a 6" slump will only slow things down.
6. Powder release
This tip only applies to those using Liquid Release. Switching to powder release in cold weather wont necessarily speed up the set time of concrete, but it will allow you to stamp it sooner and will give you a better end product. As the concrete sets slower in cold temps, it also takes longer to get rid of the bleed water. If your concrete gets to the point where it is ready to stamp but the surface is still a little bit sloppy, using liquid release will result in a lot of "pull up" on your stamps. Using powder release will lessen the "pull up" problem as well as leaving you with more defined and crisp impression.
7. Color Hardener
Using color hardener in the cold weather is another way to use up some of that slop on the surface of your concrete. color hardener also contains Portland Cement which will help speed things up. This cooler time of year is also a great opportunity to get comfortable with color hardener. It can be challenging using color hardener for the first time during the hot time of the year.
8. Covering the Sub-Grade up the night before
The temperature of sub-grade that you are pouring on is crucial in how fast the concrete will set up. Just like in the summer time when you spray water on your base to cool it down, covering it up at night before will keep it warm and will go a long way in helping your concrete set faster.
9. Concrete Blankets
The need to cover your concrete blankets might be the determining factor in deciding to hold off on pouring concrete. If you are pouring with integral color, this would probably be a smart choice. Color Hardener on the other hand is a different story. Cure lines and discoloration don't seem to be a problem when using color hardener. This topic can come with a lot of debate in the decorative concrete industry. Some would say "don't do it" while others might say "don't worry about it". From my experience, both sides are right. It all depends on how you colored the concrete.
10. Seal Next Spring
The final step in any stamped concrete job is applying the sealer. Unlike concrete, there is nothing you can add to decorative concrete sealer to make it more usable in cold weather. Applying sealer in temperatures under the recommended range will most likely end up with call back next year, and we would never recommend pushing the limits in this area. However, this does not mean that you cant pour and stamp the concrete. You just might have to wait until next spring to seal it. Make sure that your end user understands that the concrete is unsealed, but it will be fine next spring as long as they don't throw salt or anything else corrosive on it over the winter.
Please feel free to send us an email with any questions you might have about stamping in cold weather or any other topic relating to decorative concrete.