Concrete Tip of the Day #6: Surviving the Extremes – Hot and Cold Weather Concreting

Concrete doesn’t like surprises—especially not from Mother Nature. Whether the sun is blazing or a chill is in the air, temperature extremes can severely impact concrete performance. Here’s how to get it right every season.

🔥 Hot Weather Concreting: Beat the Heat

When it’s too hot, concrete loses moisture too fast and sets too quickly. This can lead to:

• Strength reduction

• Shrinkage and surface cracking

• Poor finish and crazing

  
  

Key Precautions:

• Delay pours in high winds or heat unless proper shade and moisture control are in place

• Dampen subgrade, forms, and reinforcing before placing

• Use retarders or polypropylene fibres

• Avoid delays—place and finish fast

• Cover concrete with wet hessian, polythene, or apply anti-evaporative sprays

• Start curing early and maintain ~21°C as much as possible

  
  

❄️ Cold Weather Concreting: Don’t Let It Freeze

In cold conditions, hydration slows—and in freezing temperatures, it can stop. Early frost damage can permanently weaken concrete.

Risks:

• Strength loss

• Surface scaling or spalling

• Delayed setting and poor finish

  
  

Smart Strategies:

• Never pour on frozen ground

• Use accelerators and low slump (80mm) mixes

• Insulate slabs with straw and plastic (or polystyrene)

• Start early in the day and avoid water-based curing if frost is expected

• Use curing compounds after the first night

• Avoid sealing fresh concrete unless the product is designed for cold temps

• Limit temperature drops to ≤20°C in 24 hours to avoid thermal shock

  
  

📘 What NZS 3109 Says

According to Clause 7.2.1, concrete should not be placed below 5°C on a falling thermometer or 2°C on a rising thermometer—unless proper precautions are taken.

You’re contractually responsible to protect the quality and durability of the pour. If conditions fall outside spec, document decisions and be ready to delay work if needed.

Remember:Concrete doesn’t forgive environmental abuse. Plan well, act fast, and protect early age concrete like a newborn—it’s worth every precaution.

✅ Stay tuned for the next episode of Concrete Tip of the Day!