Can I pour concrete in hot weather or cold weather?
Q: I want to pour a new sidewalk for my house, but I’m waiting for the best weather to pour concrete. What’s the ideal temperature?
A: First, let’s talk about curing. “Curing” is what happens right after you place and finish your concrete. Think about it like making a cake. Once you pour the batter into the pan, you have to bake it at the optimum temperature and time to get a tasty, fluffy dessert. Concrete is very similar. Proper curing requires the temperature and the right amount of moisture. The wrong amount can lead to weak, soggy, or cracked concrete, much like an undercooked or overcooked cake.
Concrete requires water for the cement powder to glue the rocks and sand together; not enough or too much water means the glue won’t work properly. In fact, lab tests show that concrete can lose as much as 50 percent of its potential strength if it dries without enough moisture. Cured correctly, concrete is more watertight, has a better surface hardness, and will better withstand surface wear and abrasion.
To answer your question: the best time to pour concrete is in mild temperatures above 50°F (10°C), but more importantly during a time when that temperature will stay about the same for weeks. Uniform temperature is important to properly develop strength and avoid cracking.
Q: My family wants to put in an in-ground pool this summer, but it’s really hot outside. How can I ensure the concrete sets up correctly in high heat?
When concrete is poured in hot temperatures, it generally sets up right away, but will ultimately lead to lower overall strength over time. It is important to use proper techniques during the initial cure time to prevent the concrete from drying out too fast.
Here are a few ways to maintain a consistent temperature and adequate moisture:
Layer burlap or cotton mats and rugs on top of the concrete and soak with a sprinkler or hose. Don’t let them dry out!
Cover concrete in straw and sprinkle regularly, covering with a tarp after each watering.
Directly water with a hose or sprinkler.
Create a “pond” (also known as “wet curing”) on top of the concrete with a barrier to prevent water escape.
Use chemical curing agents to help prevent rapid evaporation (this is the most common method)
More ideas from Concrete in Practice here.
Q: We’re pouring a patio in our backyard this winter to be ready in time for spring. What should I keep in mind for cold temps?
The primary downside to pouring concrete in cold weather is that it takes longer to cure. It requires more time to gain strength, which means it needs more time before forms and molds can be removed and the next step of construction can begin.
The key to cold weather concrete placement is insulation materials! As with hot weather, it’s important not to allow concrete to cool faster than a rate of 5°F (3°C) per hour for the first 24 hours. If it’s going to freeze at night, skip any kind of wet curing. Use insulating materials to protect concrete from freezing for at least the first 48 hours.