Can my new concrete freeze in Tucson AZ?
Wow! Your new concrete is on the ground and it looks phenomenal. The finish turned out better than you could have ever expected. What an amazing Crew! Whoa wait … they are putting plastic on the concrete to protect it from freezing… Can my new concrete really freeze?
As a long time Finisher, I always dreaded the days when my freshly poured masterpiece had to be covered with plastic. We avoid it as much as possible because the plastic will leave a lasting effect on the concrete in most cases. From noticeable marking to a ghost images that only appears in the rain, plastic makes it’s presence known. Don’t even get me started on insulated concrete blankets.
So, when is it necessary to cover with plastic or concrete blankets? The obvious time is when rain starts falling from the sky. The concrete needs to be covered before the top washes away. Freezing on the other hand has way more variables. In Minnesota we played the hard freeze at the end of every season. My Father established the rules I use today with years of trial and error. (Dad knew his stuff but go to concrete.org and search “guide to cold weather concreting” if you want the official stance from the powers that be)
Let me try to explain the way it was told to me. The length of the freeze has to factor in. What time did it drop below freezing and how long was it there? If it is forecasted to hit 32 degrees for one hour at 7am even a 2500 psi concrete will be producing enough heat to ward off the freeze. A 4000 psi will be good down to 27 degrees. So, what if it is forecasted to drop below freezing at midnight and stay cold til 9am? At this point the prolonged cold may do real damage to the concrete, as it freezes the water still inside. As a rule of thumb, when working with 4000 psi concrete or higher, Dad always said anything below 27 degrees fahrenheit is an automatic cover with a minimum of 6 mil plastic if a short freeze is expected. Prolonged freezes below 27 get the blankets. The cover is there to hold in the heat the concrete is producing. If covering is required and temps remain forecasted below 27, for multiple nights, keep covered for at least the first three days.
I hope that helps to explain. It’s not a major problem in Tucson but we do see freezing temps every year. If it is going to be cold during your project, you may want to have a conversation with your Contractor about the game plan.
Thank you for taking a look