Hot-Weather Concrete: Placement, Evaporation, and Curing
Planning concrete work in hot, dry, sunny, or windy conditions without relying on uncontrolled water addition.
Editorial review: 2026-09-29 · How we review technical content
Key takeaways
- Concrete can experience hot-weather problems from a combination of high ambient temperature, high concrete temperature, low relative humidity, solar radiation, and wind. These conditions can accelerate slump loss and set, increase evaporation, complicate finishing, and increase plastic-shrinkage cracking risk. A moderate air temperature with low humidity and strong wind can be more demanding than a hotter calm, humid day.
- Schedule placements for cooler periods when practical, shade aggregate or equipment, cool mixing water or use other producer measures when necessary, and reduce unnecessary haul/standby time. Ensure enough labor and equipment are available to place, strike off, finish, joint, and cure at the accelerated pace.
- Do not chase hot-weather slump loss with repeated unrecorded water additions. Work with the producer on water-reducing or retarding admixtures and the approved mixture. Any water added at the site should remain within mixture/specification limits and be documented.
Hot weather is more than air temperature
Concrete can experience hot-weather problems from a combination of high ambient temperature, high concrete temperature, low relative humidity, solar radiation, and wind. These conditions can accelerate slump loss and set, increase evaporation, complicate finishing, and increase plastic-shrinkage cracking risk. A moderate air temperature with low humidity and strong wind can be more demanding than a hotter calm, humid day.
ACI hot-weather guidance emphasizes planning concrete temperature, production, delivery, placement, protection, and curing as a system. A generic air-temperature cutoff is not a substitute for project requirements.
Plan before trucks arrive
Schedule placements for cooler periods when practical, shade aggregate or equipment, cool mixing water or use other producer measures when necessary, and reduce unnecessary haul/standby time. Ensure enough labor and equipment are available to place, strike off, finish, joint, and cure at the accelerated pace.
Prepare windbreaks, sunshades, fogging equipment where appropriate, evaporation reducer if allowed, and curing materials. Moisten absorptive subgrades/forms when permitted, but remove standing water and do not use surface water as a finishing lubricant.
Water and workability
Do not chase hot-weather slump loss with repeated unrecorded water additions. Work with the producer on water-reducing or retarding admixtures and the approved mixture. Any water added at the site should remain within mixture/specification limits and be documented.
Avoid sprinkling water onto a slab surface for finishing. Adding water at the surface can weaken the paste, increase dusting/scaling risk, and create color variation.
Curing immediately after finishing
The gap between final finishing and effective curing is especially important in hot weather. Apply the selected curing system promptly and continuously. Keep wet-curing materials wet; secure plastic against wind; apply curing compounds at the specified rate without leaving thin areas.
Monitor changing wind and humidity during the pour. Conditions at 7 a.m. may not represent those at noon, and a placement that begins comfortably can enter a high-evaporation period before finishing is complete.
Field checklist
- Review temperature, humidity, sun, and wind—not temperature alone.
- Coordinate mixture/admixtures with the producer.
- Staff for faster placement and finishing.
- Do not use surface water as a finishing aid.
- Start effective curing promptly.
References & further reading
- ACI 305 — Hot Weather Concrete resources — Hot-weather placement, protection, evaporation, and curing considerations.
- ACI PRC-308-26 — Curing of Concrete—Guide — Current ACI guidance on external curing practices and monitoring.
- ACI SPEC-301-20 — Specifications for Concrete Construction — Reference specification used when incorporated into project specifications.
- ACI PRC-302.1-15 — Guide to Concrete Floor and Slab Construction — Construction guidance for slabs-on-ground and suspended floors.
- ACI PRC-360R-10 — Guide to Design of Slabs-on-Ground — Planning/design reference for nonstructural slabs-on-ground; structural slabs may fall under ACI 318.
- NRMCA Concrete In Practice (CIP) — Industry education covering common concrete field problems and practices.