Concrete Evaporation Rate Calculator (USA)
Concrete Evaporation Rate Calculator — USA
Instantly calculate the moisture evaporation rate from fresh concrete surfaces using the official ACI 305R formula. Know your plastic shrinkage cracking risk before you pour — based on air temp, concrete temp, humidity & wind speed.
💧 Concrete Evaporation Rate Calculator — USA (ACI 305R)
Enter your site conditions to calculate evaporation rate and plastic shrinkage cracking risk level.
Ambient air temperature at the pour site. Typical US summer: 75–100°F.
Fresh concrete temperature at delivery. ACI 305R max recommended: 95°F.
Site relative humidity (RH). Check local weather or use a hygrometer on site.
Wind speed at slab surface level — typically lower than reported weather station speed.
Enter slab area to calculate total moisture loss per hour (optional).
Helps refine precaution recommendations for your region.
📋 Calculation Summary
🛡️ Recommended Precautions
⚠️ ACI 305R Evaporation Rate Risk Scale
💧 Concrete Surface Evaporation — How the ACI 305R Formula Works
Evaporation Rate depends on: Air Temp · Concrete Temp · Humidity · Wind Speed
What Is Concrete Evaporation Rate & Why Does It Matter in the USA?
The concrete evaporation rate is the speed at which water evaporates from the surface of freshly placed concrete before it has set. When this rate is too high, the concrete surface dries faster than bleed water can rise to replace lost moisture — causing the surface to shrink and crack while the concrete body is still plastic (unhardened). This is known as plastic shrinkage cracking and is one of the most common and preventable concrete defects on US job sites. According to the American Concrete Institute (ACI), any evaporation rate above 0.20 lb/ft²/hr requires immediate protective action.
🔵 The ACI 305R Critical Threshold — 0.20 lb/ft²/hr
The ACI 305R standard for hot weather concreting establishes 0.20 lb/ft²/hr as the action threshold. Below this rate, normal curing methods are sufficient. At or above this rate, contractors must implement protective measures — fogging, windbreaks, evaporation retarder sprays, or scheduling the pour during cooler hours — before and immediately after finishing the concrete surface.
🌡️ Air Temperature Effect
Every 10°F increase in air temperature approximately doubles the evaporation rate. Pouring concrete when air temperatures exceed 90°F — common in Texas, Arizona, Florida, and Southern California summers — dramatically increases plastic shrinkage cracking risk without proper precautions.
🌬️ Wind Speed Effect
Wind is the single most powerful evaporation accelerator. A 10 mph wind on a warm day can increase the evaporation rate by 3–5× compared to still air. Wind breaks — temporary plywood panels or commercial wind screens — are the most effective and affordable countermeasure on US job sites.
💧 Relative Humidity Effect
Low humidity supercharges evaporation. In arid regions like Nevada, Arizona, New Mexico, and West Texas, relative humidity routinely drops below 20–30% during summer afternoons, pushing evaporation rates to critical levels even at moderate temperatures and wind speeds.
ACI 305R Concrete Evaporation Rate Formula Explained
The ACI 305R evaporation rate formula is the industry-standard method used by engineers and concrete contractors across the United States to predict plastic shrinkage cracking risk before and during a pour. It takes four measurable site conditions and produces an evaporation rate in pounds of water lost per square foot per hour (lb/ft²/hr).
📐 ACI 305R Evaporation Rate Formula (US Imperial Units)
⚠️ Hot Weather Pouring — Plan Ahead, Not After
By the time plastic shrinkage cracks appear on a concrete surface — typically 1–6 hours after placement — the damage is done and cannot be repaired by troweling or wetting the surface. The concrete evaporation rate must be calculated before the pour begins, ideally the night before using the next-day weather forecast. If the rate is predicted to exceed 0.20 lb/ft²/hr, adjust your pour time, pre-wet the sub-base, erect wind breaks, or apply a concrete evaporation retarder spray immediately after screeding.
Concrete Evaporation Rate Reference Table — USA Conditions (2026)
The table below shows calculated evaporation rates under typical US weather scenarios using the ACI 305R formula. Use this as a quick field reference to assess risk without running the full calculation. All values assume a concrete temperature 5°F above air temperature, which is typical for summer morning pours.
| Scenario | Air Temp (°F) | Humidity (%) | Wind (mph) | Evaporation Rate | Risk Level |
|---|---|---|---|---|---|
| Cool Morning Pour | 65°F | 70% | 5 mph | 0.04 lb/ft²/hr | ✅ Low Risk |
| Mild Spring Day | 75°F | 55% | 8 mph | 0.10 lb/ft²/hr | ✅ Low–Moderate |
| Warm Summer Afternoon | 85°F | 45% | 10 mph | 0.19 lb/ft²/hr | ⚠️ Moderate — Monitor |
| Hot Summer Day (South USA) | 90°F | 40% | 15 mph | 0.31 lb/ft²/hr | 🔴 HIGH — Action Required |
| Desert Afternoon (AZ / NV) | 100°F | 20% | 15 mph | 0.60 lb/ft²/hr | 🔴 CRITICAL — Reschedule |
| Windy Hot Day | 88°F | 35% | 25 mph | 0.55 lb/ft²/hr | 🔴 CRITICAL — Wind Break Needed |
| Overcast Humid Day | 78°F | 80% | 5 mph | 0.03 lb/ft²/hr | ✅ Very Low Risk |
✅ Cool Morning Pour
⚠️ Warm Summer Afternoon
🔴 Hot Summer Day (South USA)
🔴 Desert Afternoon (AZ / NV)
🔴 Windy Hot Day
✅ Overcast Humid Day
How to Reduce Concrete Evaporation Rate on US Job Sites
When your concrete evaporation rate calculation shows a moderate or high risk, these field-proven precautions — recommended by ACI 305R and used by professional concrete contractors across the USA — can significantly reduce plastic shrinkage cracking risk and protect your slab finish.
🌬️ Erect Wind Breaks
Temporary plywood panels or commercial wind screens around the pour area can reduce wind speed at slab level by 60–80%. This is the single most cost-effective precaution when wind speed exceeds 10 mph on a warm day. Stakes and plywood cost under $50 for a typical residential slab.
💦 Apply Evaporation Retarder
Concrete evaporation retarder sprays (such as Confilm by BASF or Eucobar) form a monomolecular film on the freshly screeded surface that reduces evaporation by 60–80%. Apply immediately after screeding and before final finishing. Cost is approximately $30–$60 per gallon covering 500–800 sq ft.
🌅 Schedule Pours for Early Morning
In Southern and desert US states, scheduling pours to begin at dawn (5–7 AM) and finish before noon takes advantage of cooler temperatures, higher morning humidity, and lower wind speeds — typically reducing evaporation rates by 40–70% compared to midday pours in the same conditions.
🔵 Pre-Cool the Concrete Before Delivery
In hot weather, request that your ready-mix supplier use chilled mix water or ice to lower the concrete delivery temperature. ACI 305R recommends keeping fresh concrete at or below 85–90°F at the point of placement. Every 10°F reduction in concrete temperature reduces the evaporation rate by approximately 20–25%. Major US ready-mix suppliers including Quikrete and regional batch plants can accommodate this request with 24–48 hours advance notice.
❓ Frequently Asked Questions — Concrete Evaporation Rate Calculator (USA)
- Low (<0.10 lb/ft²/hr): Normal curing practices — no special precautions needed
- Moderate (0.10–0.20 lb/ft²/hr): Monitor conditions, have precautions ready
- High (0.20–0.50 lb/ft²/hr): Immediate action required — wind breaks, retarder spray, or fogging
- Critical (>0.50 lb/ft²/hr): Consider rescheduling — pour only with full precaution suite in place
- Calculate evaporation rate before the pour using ACI 305R formula
- Apply an evaporation retarder spray immediately after screeding
- Erect wind breaks when wind exceeds 10 mph
- Use fogging or misting near (not on) the concrete surface
- Schedule pours in early morning during hot weather months
- Add polypropylene or steel fiber reinforcement to concrete mix
- Below 90°F air temp: Generally safe with standard hot weather precautions
- 90–100°F air temp: Higher risk — requires evaporation retarder, wind breaks, and pre-cooled mix water
- Above 100°F air temp: Very high risk — reschedule to early morning or evening; use ice in mix water and chilled aggregates
- Concrete delivery temp above 95°F: ACI 305R recommends rejecting the load
- Air temperature: Use a digital thermometer at pour site level (not the truck cab or shaded area)
- Concrete temperature: Insert a calibrated concrete thermometer 3–4 inches into the fresh mix immediately after discharge
- Relative humidity: Use a digital hygrometer or psychrometer at the job site — do not rely solely on weather apps which measure conditions at the weather station
- Wind speed: Use a pocket anemometer held at slab surface height — wind is typically 30–50% lower at ground level than at the 10-meter weather station height
📚 Trusted US Concrete & Hot Weather Concreting Resources
Official standards and guides used by US concrete engineers and contractors for evaporation rate management.
ACI 305R — Hot Weather Concreting
Official US StandardACI 305R is the official American Concrete Institute guide for hot weather concreting, covering the evaporation rate formula, plastic shrinkage cracking prevention, mix design adjustments, and field precautions for high-temperature and high-wind conditions across the USA.
ACI Formulas & ToolsPortland Cement Association — Hot Weather Guide
Industry ReferenceThe Portland Cement Association (PCA) provides detailed guidance on hot weather concreting practices, evaporation rate charts, mix water temperature control, and curing best practices for residential and commercial concrete construction across US climates.
Read PCA GuideQuikrete — Hot Weather Concreting Tips
DIY & Contractor GuideQuikrete's hot weather concreting guide covers practical steps for homeowners and contractors to protect fresh concrete during high-temperature pours — including evaporation retarders, proper curing timing, and scheduling recommendations for summer projects across the USA.
Quikrete Hot Weather Guide