Pouring Concrete in Summer: Heat Precautions

Pouring Concrete in Summer Heat: Complete Protection Guide

Summer heat creates major challenges for concrete placement. High temperatures cause rapid setting, excessive water loss, and thermal cracking. Without proper precautions, your concrete will fail. This guide covers exactly how to handle hot weather concrete placement successfully.

Why Heat is a Problem

High temperatures (above 90°F) cause:

• Rapid hydration: Concrete sets too fast, making finishing difficult or impossible
• Excessive evaporation: Water evaporates before it can hydrate cement, weakening the concrete
• Thermal cracking: Temperature differences between surface and interior create stress cracks
• Plastic shrinkage cracking: Surface dries faster than interior, causing cracks
• Reduced strength: Poor hydration results in weaker concrete

Critical Temperature Threshold: 90°F

Once temperatures exceed 90°F, special precautions become mandatory. The risk of failure increases dramatically above this threshold.

Step 1: Use Ice Water in the Mix

Start with cold concrete by using ice water in the mix.

How It Works

Adding ice to the mix water lowers the concrete temperature. This gives you more working time and slows the hydration process.

Implementation

1. Order concrete with ice water: Request this from your ready-mix supplier
2. Target mix temperature: Aim for 65-75°F initial temperature
3. Work with supplier: They'll adjust water temperature and may add ice to achieve this

Why It Matters

Every 10°F increase in concrete temperature reduces working time by approximately 20-30%. Starting with cooler concrete buys you critical time for proper placement and finishing.

Step 2: Add Retarder

Chemical retarders slow the hydration process, extending your working time.

How Retarders Work

Retarders delay the chemical reaction between cement and water, giving you more time to place, consolidate, and finish the concrete before it sets.

Types of Retarders

• Ready-mix retarder: Added by supplier during batching
• Field-applied retarder: Sprayed on surface after placing

Application

1. Request retarder in mix: Specify when ordering concrete
2. Dosage: Supplier will determine proper amount based on temperature and conditions
3. Timing critical: Retarder must be added during batching, not after

Important Notes

• Don't over-retard—can cause permanent strength reduction
• Work with experienced supplier to get dosage right
• Test on small area first if possible

Step 3: Spray Evaporation Retarder

Evaporation retarders form a film on the surface that slows water loss.

How It Works

Evaporation retarders create a thin membrane on the concrete surface that prevents water from escaping. This keeps the surface moist longer, allowing proper hydration.

Application Process

1. Apply immediately after screeding: Before concrete starts to set
2. Spray evenly: Cover entire surface
3. Reapply if needed: If surface starts to dry
4. Remove before finishing: Wipe off or allow to dissipate before final troweling

Product Types

• Commercial evaporation retarders: Specially formulated products
• Alternative: Water misting can help, but evaporation retarder is more effective

Step 4: Pour Early Morning

Timing your pour for the coolest part of the day is critical.

Best Time: Early Morning

• Optimal window: 5:00 AM to 9:00 AM
• Why: Lowest temperatures of the day
• Benefit: Gives you several hours before peak heat

Avoid Mid-Day

• Worst time: 11:00 AM to 3:00 PM
• Why: Peak temperatures, maximum sun exposure
• Risk: Concrete will set too fast, excessive evaporation

Late Afternoon/Early Evening

• Alternative: After 4:00 PM
• Consideration: Temperatures dropping, but less daylight for finishing
• Use if: Morning not possible, but have adequate lighting

Additional Hot Weather Precautions

Cool the Subgrade

Hot ground heats the concrete from below:

• Mist subgrade with water before placing concrete
• Keep it wet and cool
• This prevents bottom heating while top cools

Shade the Work Area

Direct sun significantly increases surface temperature:

• Set up shade screens or tarps
• Keep concrete out of direct sun during placement
• Continue shading during initial curing

Cool Your Tools

Hot tools can cause problems:

• Keep tools in shade
• Cool with water if needed
• Hot screeds or trowels can scorch concrete surface

Have Extra Help Ready

Hot weather concrete moves fast:

• Have full crew ready before truck arrives
• Work quickly and efficiently
• No delays—concrete won't wait

Monitoring During Placement

Watch for These Signs

• Concrete setting too fast: Getting stiff before you can finish it
• Surface drying: Cracking or "checking" on surface
• Plastic shrinkage: Cracks appearing during placement

If Problems Occur

• Stop placement: Don't continue if concrete is setting
• Mist with water: Keep surface moist
• Consider rescheduling: Better to wait than create a failure

Post-Placement Protection

Immediate Curing

Start curing immediately after finishing:

• Apply curing compound or cover with wet burlap
• Keep surface continuously moist
• Don't let it dry out

Extended Protection

Continue protection for several days:

• Keep covered and moist
• Protect from direct sun
• Mist with water as needed

When to Reschedule

Consider rescheduling if:

• Temperatures exceed 95°F
• High humidity makes it feel even hotter
• Strong winds increase evaporation
• You don't have proper equipment/precautions

The Bottom Line

Pouring concrete above 90°F requires ice water mix, retarder, and evaporation retarder. Pour early morning (5-9 AM) to avoid peak heat. Protect with shade, keep subgrade cool, and cure immediately. Without these precautions, hot weather will cause rapid setting, excessive evaporation, and cracking. When done correctly with proper precautions, summer concrete can succeed, but it requires careful planning and execution.

Need to pour in hot weather? Contact Local Concrete Contractor. We have the experience, equipment, and techniques to handle summer concrete placement successfully.