Heatwave delays concrete pours

The UK June heatwave caused construction sites to postpone concrete pours as temperatures exceeded 35C.

With more hot weather anticipated, the Health & Safety Executive (HSE) said that employers should view extreme hot weather as a health hazard. The UK Health Security Agency (UKHSA) issued red heat health alert warnings for most of England and Wales in June 2026.

Many construction sites responded to the warnings by limiting activities. Major concrete pours on the HS2 sites were postponed. Water and sun cream were available on site, and regular breaks were taken during the hottest periods.

At the Hinkley Point C site, priority was given to indoor work in the underground galleries where workers are kept cool by thick concrete structures.

Temperatures over 25 °C cause issues with concrete flooring pours as water evaporates too quickly. This can reduce the strength of the structure’s concrete and increase the risk of cracking and shrinkage. The timing of pours can be changed to avoid the hottest hours of the day. Before the pour, cement and aggregates should be stored in a cool, dry area. The sub-base can be damped to prevent moisture absorption.

Though there is no legal maximum temperature for working, the HSE says that very hot weather should be treated as a health hazard. Employers must support all workers when temperatures rise. There should be good ventilation, access to drinking water and weather-appropriate personal protective equipment (PPE) provided. The HSE said that employers should consider having more staff on a work shift to enable increased staff breaks.