Hot Weather Concrete: 5 Tips to Prevent Rapid Drying and Cracking
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When temperatures rise above 90°F (32°C), pouring concrete becomes a race against time. High heat, low humidity, and wind create a "perfect storm" that causes the water in the mix to evaporate too quickly. This leads to "plastic shrinkage cracks," which look like spiderwebs across your beautiful new slab.
1. The Early Bird Gets the Best Pour
Schedule your concrete delivery for the earliest possible slot—usually 6:00 or 7:00 AM. The ground is cooler, the air is more humid, and you'll be finished before the punishing midday sun hits the wet concrete. If the temperature is expected to be over 100°F, many professionals will wait for a cooler day entirely.
2. Dampen the Sub-Base
A dry gravel base acts like a sponge, sucking the water right out of the bottom of your concrete. Lightly mist your gravel with a hose right before the pour. You want it damp, but with no standing puddles. This keeps the moisture in the concrete where it belongs.
3. Use "Set Retarders"
Talk to your ready-mix supplier about adding a "retarder" admixture. This chemical slows down the hydration process, giving you an extra 30 to 60 minutes of "workability" time to get the concrete leveled and finished before it gets too hard to move.
4. Don't Add Too Much Water on Site
It's tempting to tell the driver to "wet it up" so it flows easier in the heat. Resist this urge! Extra water dilutes the cement paste and dramatically lowers the strength of your slab. If you need more flow, ask for a "superplasticizer" instead.
5. Begin Curing Immediately
In hot weather, start your curing process the moment you finish the final pass with the trowel. Use a spray-on curing compound or a fine mist of water. Keeping the surface moist is the only way to prevent the top layer from drying faster than the bottom layer, which is the primary cause of curling and cracking.
Plan your hot-weather pour carefully by using our instant concrete calculator to ensure you have all your tools and help ready before the truck arrives.