Hot Weather Concreting: Tips for Pouring in Heat
Hot weather concreting means planning around fast setting and rapid evaporation. When air temperatures climb into the 90s, or wind and low humidity dry the surface quickly, concrete can stiffen before it is finished, form plastic shrinkage cracks, develop cold joints, or end up with a weak, dusty surface. The fixes are about timing, cooling, and fast curing.
Concrete calculator →What heat does to concrete
- Faster setting: less time to place and finish.
- Higher water demand: crews are tempted to add water, which weakens the mix.
- Rapid evaporation: the surface dries faster than bleed water rises, causing cracks.
- Lower long-term strength if the concrete cures hot and dry.
Planning the pour
- Pour early in the morning or in the evening.
- Order a retarder to slow setting. Ask the plant for its hot weather mix.
- Have enough crew for the slab size. Heat shortens the window.
- Schedule trucks closely to avoid cold joints. See concrete cold joint.
- Have curing materials ready before the first truck arrives.
Cooling the job
- Dampen the base and forms so they do not pull water from the concrete, without leaving puddles.
- Shade the work area if possible.
- Use windbreaks on windy days.
- Plants can use chilled water or ice in the mix for big jobs.
Evaporation retarders
Spray-on evaporation retarders form a thin film that slows surface moisture loss between finishing steps. They are not curing compounds, but they help prevent plastic shrinkage cracks.
Finishing
Avoid adding water to the surface to make it easier to finish. That leads to crazing and dusting. See concrete crazing. Finish promptly and avoid overworking.
Curing
Start curing as soon as finishing is done:
- Curing compound sprayed evenly. See concrete curing compound.
- Wet curing with soaker hoses, wet burlap, or curing blankets. See wet curing concrete.
- Plastic sheeting weighted at edges.
Keep curing for at least 7 days for best results.
Warning signs
| Sign | What it means |
|---|---|
| Surface drying before finishing | Evaporation too fast |
| Short parallel cracks | Plastic shrinkage |
| Hard to finish, tearing | Mix setting too fast |
Bagged concrete in the heat
Hand-mixed bags set just as fast in hot weather, and small crews fall behind easily. Keep bags in the shade so the mix starts cooler, use cool water from an indoor tap rather than a hose that has sat in the sun, and mix smaller batches so each one is placed within a few minutes. Wet the forms and base just before each section. If you are working alone, a fast-setting post mix is fine for posts, but for a slab it is better to wait for a cooler morning or bring in more help.
Bottom line
In hot weather, pour early, use a retarder, dampen the base, shade and windbreak when possible, never add water to the surface, and start curing immediately. Those steps prevent most hot weather cracks and weak surfaces.
Questions people ask
What temperature is too hot to pour concrete?
Many guidelines flag concrete temperatures above about 90°F as hot weather concreting that needs extra precautions.
Should I wet the ground before pouring concrete in hot weather?
Dampen the base without leaving standing water.
What is a concrete retarder?
An admixture that slows setting, giving more time to place and finish.
Can I spray water on concrete while finishing?
Avoid it. Adding water to the surface weakens it and causes crazing.
How long should concrete cure in hot weather?
At least 7 days of moist curing or a curing compound is a common goal.
Related guides
- Concrete Cold Joint: What It Is and How to Avoid It
- Concrete Crazing: Fine Surface Cracks and Causes
- Concrete Curing Compound: What It Does and How to Use
- Wet Curing Concrete: Methods, Timing, and How Long
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