As we head into the fall season, have you ever had trouble with the surface of your concrete drying out and becoming less workable? You may have also had this problem come up in the springtime when the days are getting warmer, but it still cools down at night. The surface of the concrete becomes dry and crusty, but the concrete underneath it is still soft. When you try to stamp it, you get a bunch of tinny surface cracks. If this has happened to you, we might have a few things that could help.
The reason this happens is that the ground is cold from the overnight temperatures and so are the materials that make up the concrete. So, when this cold concrete is poured onto the cold ground, it doesn't want to set up very fast. But if the sun is out and the wind is blowing, the surface of the concrete will start to dry out and skin over. This will make for a really bad day no matter how you are trying to finish your concrete. There are however, a few things we can do to fight back against this problem.
Some Solutions -
The first thing is to use a finishing aid or evaporation retarder. The one that I have the most experience with is Control Finish. Which is a finishing aid as opposed to an evaporation retarder like Deco-Film. The difference is that a finishing aid will add moisture to the surface and a retarder will retain the moisture that is already in the concrete. Finishing aids are made to float into the concrete, while evaporation retarders are meant to be sprayed on after floating and not worked in.
Control Finish typically works best for stamped concrete, especially when using color hardeners. Deco-Film works great for broom finished concrete or on large areas that may be hard to reach.
Another thing that can be helpful is to use accelerator to speed up the set time of the concrete. This may not seem logical since we are trying to keep the top from drying out too fast, but the main point is that we need to get the bottom of the concrete and the surface to set up as uniformly as possible. This may mean slowing down the top or it might mean speeding up the bottom. In some cases, it may even mean a little of both. Using accelerators this time of year can be tricky and you need to work with your ready-mix plant for proper dosage. Make sure you are using a Non-Chloride Accelerator (NCA), this will be more forgiving than calcium flake and does not affect the color in decorative concrete.
Final Thoughts -
As we transition from summer into fall, and you start to notice the surface of your concrete crusting over and becoming hard to work with, just remember that there are things you can do to reduce the effects of this problem.
- Jeff Hershberger