Question 1

What is a safe evaporation rate for concrete?

Accepted Answer

ACI 305R recommends taking precautions when the concrete evaporation rate exceeds 0.15 lb/ft²/hr. Above this threshold, surface moisture evaporates faster than bleed water can replace it, causing plastic shrinkage cracking — especially critical with blended cements like Type 1L. PourDay calculates your real-time evaporation rate automatically using live weather data for your job site zip code.

Question 2

How do I know if it's safe to pour concrete today?

Accepted Answer

Safe pour conditions depend on four variables: air temperature, relative humidity, wind speed at 18 inches above the slab, and concrete temperature. PourDay plugs your real-time job site weather into the ACI 305R evaporation formula and gives you a GO, CAUTION, or NO GO result in seconds — no math, no nomograph.

Question 3

How do I prevent plastic shrinkage cracking in concrete?

Accepted Answer

Plastic shrinkage cracking is caused by high evaporation conditions pulling moisture from fresh concrete before bleed water can replace it. When evaporation rates exceed 0.15 lb/ft²/hr, use evaporation retarders, erect wind breaks, adjust pour timing, or lower concrete temperature. PourDay shows you the real-time evaporation rate for your exact job site so you can make that call proactively.

Question 4

What is PourDay?

Accepted Answer

PourDay is a free mobile app that gives concrete contractors a real-time concrete evaporation rate calculator using the ACI 305R formula, 16-day job site forecasts, and a pour log — helping crews make accurate go/no-go pour decisions before leaving the yard.

Question 5

How does PourDay calculate evaporation rate?

Accepted Answer

PourDay uses the ACI 305R evaporation rate formula, combining air temperature, concrete temperature, relative humidity, and wind speed from live weather data to calculate surface moisture loss. Conditions are scored as GO, CAUTION, or NO GO based on the 0.15 lb/ft²/hr ACI threshold.

Question 6

Is PourDay free?

Accepted Answer

Yes, PourDay is completely free for contractors. No subscription, no paywall, no premium tier.

Question 7

What is ACI 305R?

Accepted Answer

ACI 305R is the American Concrete Institute's guide for hot weather concreting. It defines evaporation rate thresholds — specifically 0.15 lb/ft²/hr — that indicate when plastic shrinkage cracking risk increases, especially important with modern blended cements like Type 1L.

Question 8

Can I track multiple job sites?

Accepted Answer

Yes, PourDay supports up to 10 saved locations. Each location gets its own real-time evaporation rate, 16-day forecast, and pour condition scoring.

Concrete Guides for Contractors.

Plastic Shrinkage Cracking in Concrete

Concrete Evaporation Rate: The Complete ACI 305R Guide

Concrete Curing: Time, Methods & How Evaporation Affects It

ACI 305R Explained: Hot Weather Concreting

Concrete Retarder vs Accelerator: When to Use Each

Concrete Slump Test: What It Means for Pour Conditions

Free Evaporation Rate Calculator

Know Before You Pour.