Hot Weather Concrete Pouring Guide

Concrete and heat have a complicated relationship. Some of the most damaging concrete failures happen not in the dead of winter but during the hottest days of summer. Slabs that crack before the finishers even leave the site. Walls that set so fast the crew cannot vibrate them properly. Flatwork that develops a maze of plastic shrinkage cracks within two hours of placement.

The problem is not that concrete cannot be placed in hot weather. Contractors in Arizona, Texas, Florida, and other warm climates pour concrete all summer long. The problem is that hot weather demands adjustments to nearly every part of the process, and many contractors do not make them until something goes wrong.

This guide covers the challenges of hot weather concreting, the specific steps you need to take, and how to avoid the failures that ruin good concrete on hot days.

Why Heat Is the Enemy of Good Concrete

Heat accelerates everything about concrete that you want to control. Hydration speeds up, water evaporates faster, workability disappears, and the window for proper placement and finishing shrinks dramatically.

Here is what heat does to concrete:

Faster Hydration and Set Time

The chemical reaction between cement and water (hydration) is temperature-dependent. For every 18°F (10°C) increase in concrete temperature, the rate of hydration roughly doubles. This means:

• A mix that gives you 90 minutes of workability at 70°F might give you only 45 minutes at 90°F
• Slump loss during transit is accelerated, meaning the concrete arriving on site is stiffer than expected
• Initial set may occur before placement and consolidation are complete, leading to cold joints and poor vibration

Increased Water Demand

Hot concrete needs more water to maintain the same slump. But adding water at the job site to restore workability increases the water-to-cement ratio, which directly reduces strength, increases shrinkage, and hurts durability.

This is one of the most common mistakes in hot weather: the concrete arrives stiff, someone adds water to make it workable, and the final product is weaker than designed.

Rapid Moisture Evaporation

High air temperature, low humidity, and wind all accelerate evaporation from the concrete surface. When evaporation exceeds the rate of bleed water rising to the surface, the top layer dries out while the concrete below is still plastic.

This differential shrinkage is what causes plastic shrinkage cracks, one of the most visible and frustrating problems in hot weather concreting.

Higher Early Strength, Lower Ultimate Strength

Concrete placed at high temperatures gains strength faster in the first few days. This might seem like a benefit, but it comes at a cost. The rapid hydration produces a cement paste with a less organized crystalline structure, resulting in lower 28-day strength and reduced long-term durability.

Concrete placed at 90°F may have 7-day strengths 10% to 15% higher than concrete placed at 73°F, but 28-day strengths that are 5% to 10% lower. Over time, this gap can widen.

Increased Risk of Thermal Cracking

In thicker sections (foundation walls, mat foundations, grade beams), the heat generated by hydration cannot escape quickly from the interior. In hot weather, the concrete starts at a higher temperature, so the peak internal temperature is even higher. The temperature differential between the hot interior and the cooler surface creates thermal stresses that can crack the element.

ACI 305: Hot Weather Concreting Guidelines

ACI 305R, “Guide to Hot Weather Concreting,” is the industry standard reference. Unlike cold weather guidelines that define conditions by specific temperatures, ACI 305 takes a broader approach.

Hot weather conditions exist when any of these factors are present:

• High ambient temperature
• High concrete temperature
• Low relative humidity
• High wind speed
• Direct solar radiation

The standard recognizes that hot weather problems are not caused by temperature alone. A 90°F day with 70% humidity and calm winds is much less aggressive than an 85°F day with 15% humidity and 20 mph winds.

ACI 305 recommendations include:

• Keep concrete temperature as low as practical at placement
• Use concrete materials and proportions with a satisfactory record in hot weather
• Plan and execute the work to reduce delays during placement
• Begin curing as soon as practical
• Protect against moisture loss from exposed surfaces

Cooling the Concrete

The single most effective thing you can do for hot weather concrete is lower the temperature of the concrete itself before it arrives on site.

Cooling Mix Water

Water has the highest heat capacity of any concrete ingredient. Lowering the water temperature has the greatest effect on concrete temperature per degree of cooling.

Rule of thumb: Reducing mix water temperature by 10°F lowers concrete temperature by approximately 2°F. Reducing aggregate temperature by 10°F lowers concrete temperature by approximately 5°F (because there is much more aggregate than water in the mix).

Methods for cooling water:

• Refrigerated water storage at the batch plant
• Adding ice as part of the mix water (must be fully melted by the time mixing is complete)
• Chilled water delivery from ice companies

Using ice: Ice is one of the most effective cooling methods. The phase change from solid to liquid absorbs a large amount of heat. Flaked or crushed ice is preferred over block ice because it melts faster during mixing. The ice must be completely melted before the concrete leaves the mixer, or you will have pockets of excess water in the mix.

Cooling Aggregates

Aggregates make up 60% to 75% of the concrete volume, so their temperature has a major impact on concrete temperature. Aggregate stockpiles sitting in direct sun can reach 120°F or higher.

Methods:

• Spray stockpiles with water to cool by evaporation (account for the additional moisture in your mix design)
• Shade aggregate bins from direct sun
• Use lighter-colored aggregate if available (absorbs less solar radiation)

Liquid Nitrogen

For large projects with strict temperature requirements, liquid nitrogen can be injected into the mixer drum at the batch plant. This brings concrete temperature down rapidly and precisely. It is expensive ($20 to $40 per cubic yard for the nitrogen alone) but may be the only way to meet specifications calling for placement temperatures below 70°F on a 100°F day.

Mix Design Adjustments

Work with your ready-mix supplier to adjust the mix for hot weather conditions.

Cement type: Type II cement generates less heat during hydration than Type I. Blended cements with fly ash or slag also reduce heat generation and extend set times, giving you more working time.

Supplementary cementitious materials (SCMs): Replacing 15% to 30% of the portland cement with fly ash or 30% to 50% with slag reduces the heat of hydration, slows early strength gain, and extends workability. The tradeoff is slower early strength development, which may affect form stripping schedules.

Retarding admixtures: Chemical retarders slow the hydration process, extending set time and workability. These are almost always used in hot weather concreting. The dosage needs to be adjusted for the actual temperature conditions, so coordinate with your supplier.

Avoid adding water at the site. If the concrete arrives with lower slump than expected, use a mid-range water reducer or superplasticizer to restore workability without increasing the water content. Adding water is the most damaging thing you can do to a hot weather mix.

Air entrainment: Hot weather makes air entrainment harder to maintain. Higher concrete temperatures and longer mixing times tend to reduce the air content. Test air at the point of placement (not at the truck) and work with your supplier to adjust dosing.

Planning the Pour

Timing

The simplest way to avoid hot weather problems is to pour when it is not hot.

• Early morning pours: Starting at 4:00 or 5:00 AM means the bulk of placement and finishing happens before peak temperatures. This is the most common approach.
• Night pours: For large pours in extreme heat, working through the night eliminates solar radiation and drops ambient temperatures by 15°F to 30°F. Night pours require lighting, traffic control (if applicable), and crew scheduling adjustments.
• Avoid midday placement. Placing concrete between noon and 4:00 PM during peak summer is asking for problems.

Speed

Everything moves faster in hot weather, so your placement plan needs to keep pace.

• Minimize time from batching to placement. Keep haul times under 45 minutes in hot weather. Longer hauls mean more slump loss and higher concrete temperatures on arrival.
• Increase crew size for finishing. You have less time between placement and initial set, so you need more finishers to cover the area before the concrete gets away from them.
• Stage materials and equipment in advance. Do not waste minutes looking for a bull float or waiting for a pump hose extension. Everything should be positioned and ready.
• Reduce batch sizes if necessary. Smaller loads mean less time per truck, which means less time for the concrete to lose workability.

Subgrade and Form Preparation

Hot subgrades and forms steal moisture from the bottom of the pour.

• Moisten the subgrade before placement. It should be damp, not muddy. A dry subgrade will suck water out of the concrete, causing the bottom of the slab to dehydrate.
• Cool metal forms by spraying with water before placement. Dark steel forms in direct sun can reach 150°F or higher.
• Never pour on hot, dry subgrade. The concrete will lose moisture from the bottom while it is evaporating from the top, creating a double-drying condition that leads to curling and cracking.

Placement and Finishing

Reduce Exposure Time

The clock starts as soon as concrete is exposed to air. Every square foot of exposed surface is losing moisture.

• Do not dump and spread too far ahead of the finishing crew. Place and finish in a continuous operation with minimal lag time.
• Use sunshades over fresh concrete if possible. Even temporary shade from a portable canopy reduces surface temperature and evaporation rate.
• Apply evaporation retarder (monomolecular film) to the surface immediately after screeding. This product forms an invisible film on the surface that reduces evaporation by up to 80%. It is not a curing compound; it is a temporary measure to reduce moisture loss during finishing. It dissipates during troweling.

Finishing in the Heat

• Do not start finishing operations while bleed water is present on the surface. This rule applies in all weather, but in hot weather the bleed water may appear and disappear quickly, tempting finishers to start too early or work bleed water into the surface.
• Watch for rapid surface drying. If the surface starts to look matte or dry before finishing is complete, apply evaporation retarder or mist lightly with water (fogging, not soaking).
• Complete finishing operations quickly. The window between initial set and final set is compressed in hot weather. If you miss the window, you get surface defects that cannot be corrected.

Fogging

Fogging is the application of a fine mist of water over the concrete surface to increase humidity and reduce evaporation. It is different from spraying or ponding. The droplets should be so fine they feel like fog, not rain.

When to fog: When the evaporation rate at the surface exceeds 0.25 lb/ft²/hour (use the ACI evaporation rate nomograph to calculate). Conditions with high temperature, low humidity, and wind often exceed this threshold.

Caution: Do not fog so heavily that water collects on the surface. Standing water on fresh concrete before it has set will weaken the surface layer.

Curing: The Most Critical Step

If you do nothing else right in hot weather concreting, get curing right. Inadequate curing in hot conditions is the single biggest cause of concrete surface failures.

Start curing immediately after finishing. In hot weather, this might mean within 20 to 30 minutes of placement.

Curing Methods for Hot Weather

Curing compounds: Spray-on membrane-forming compounds that seal moisture in. Apply immediately after finishing at the manufacturer’s recommended rate. Do not thin the compound. One coat may not be enough in extreme conditions; apply two coats in perpendicular directions.

Wet curing: Covering the surface with wet burlap, cotton mats, or similar materials, then keeping them continuously wet for at least 7 days. This is the gold standard for curing but is labor-intensive. The coverings must never be allowed to dry out, as dry burlap will actually wick moisture out of the concrete.

Ponding: Flooding the surface with 1 to 2 inches of water, contained by earth dams or plastic sheeting around the perimeter. Very effective but only practical for flat, level surfaces.

Plastic sheeting: Placed directly on the concrete surface after finishing. Seals in moisture effectively but can cause discoloration (dark and light patches) if the sheeting is not in full contact with the surface. This matters for decorative or architectural concrete.

Curing Duration

In hot weather, cure for a minimum of 7 days. For concrete with supplementary cementitious materials (fly ash, slag), extend curing to 10 to 14 days because these mixes gain strength more slowly.

Many contractors pull curing measures after 3 days because the surface “looks hard.” In hot weather, the surface might look hard but the concrete has not developed adequate strength and durability through its full depth. Three days is not enough.

Evaporation Rate: The Number You Need to Know

The ACI 305 evaporation rate chart (or nomograph) is the most important tool for hot weather concreting. It calculates the rate of moisture evaporation from a concrete surface based on four variables:

1. Air temperature
2. Relative humidity
3. Concrete temperature
4. Wind speed

Critical threshold: When the evaporation rate exceeds 0.20 lb/ft²/hour, precautionary measures are required. Above 0.25 lb/ft²/hour, plastic shrinkage cracking is highly likely without intervention.

Example scenarios:

That last scenario is not unusual in the desert Southwest or parts of Texas during summer. At 0.55 lb/ft²/hr, you are fighting a losing battle without aggressive evaporation control.

Download the ACI evaporation rate chart and keep it on the job site. Calculate the rate before every hot weather pour. It takes 60 seconds and tells you exactly what precautions you need.

Common Hot Weather Concrete Failures

Plastic Shrinkage Cracks

What they look like: Shallow cracks, typically 1 to 3 feet long, appearing in a random or semi-parallel pattern within the first few hours after placement. They usually appear on the surface while the concrete is still plastic (before it has set).

Cause: Surface moisture evaporates faster than bleed water replaces it. The surface shrinks while the interior does not, creating tension that opens cracks.

Prevention: Control evaporation rate through fogging, evaporation retarders, windbreaks, and sunshades. Begin curing immediately after finishing.

Crusting

What it looks like: The top surface sets and skins over while the concrete beneath is still workable. When finishers try to trowel, the crust tears and leaves a rough, uneven surface.

Cause: Rapid evaporation dries the surface layer, causing it to set before the underlying concrete. Common in hot, windy, low-humidity conditions.

Prevention: Fogging, evaporation retarders, and retarding admixtures help keep the surface from setting ahead of the interior.

Cold Joints

What they look like: Visible lines in walls, columns, or slabs where one layer of concrete has set before the next layer is placed. The joint between layers is weak and may leak water.

Cause: Delays between loads of concrete allow the surface of the previously placed layer to set before the next load arrives. In hot weather, even a 30-minute delay can create a cold joint.

Prevention: Schedule tight delivery intervals, have backup trucks available, and apply retarder to exposed surfaces during any delays.

Reduced Long-Term Strength

What it looks like: 28-day cylinder breaks come back below design strength even though 7-day breaks looked good.

Cause: High placement temperatures produced rapid early hydration with a disorganized crystal structure. The concrete “peaked” early and did not develop full strength.

Prevention: Lower concrete placement temperature, use SCMs to slow hydration, and maintain proper curing for the full recommended duration.

Thermal Cracking in Mass Concrete

What it looks like: Deep cracks appearing in thick elements (mat foundations, thick walls, large footings) within the first week.

Cause: The interior of the element reaches very high temperatures from hydration heat. The surface cools faster, creating a temperature differential that exceeds the tensile strength of the concrete. The higher the starting temperature, the worse this gets.

Prevention: Lower placement temperature, use low-heat cements and SCMs, install cooling pipes in mass concrete elements, and insulate the surface to reduce the temperature gradient.

Cost Impacts of Hot Weather Concreting

Like cold weather, hot weather adds cost to concrete work. Budget for it.

For a 200-CY pour in extreme heat, expect $3,000 to $10,000 in additional hot weather costs. Night pours add crew premium costs on top of that.

Documentation

Just like cold weather, document your hot weather pours thoroughly.

Record:

• Air temperature, humidity, and wind speed at the time of pour
• Concrete temperature at delivery and at placement
• Evaporation rate calculation
• Mix design and any adjustments (retarders, ice, chilled water)
• Placement start and finish times
• Curing method applied and time of application
• Finishing start and completion times
• Any problems observed (rapid set, cracking, crusting)
• Cylinder data (field-cured and lab-cured for comparison)

This documentation protects you when questions arise about concrete quality months or years later.

ACI 305 Hot Weather Requirements in Practice

ACI 305R is the foundational reference document, but understanding how to apply it on actual job sites requires more than reading the standard. Here is how the key provisions translate into daily decisions for concrete contractors.

Temperature Limits and Specification Language

ACI 305 does not prescribe a single maximum concrete temperature. Instead, it recommends that concrete temperature be “as low as practical” and defers to project specifications for hard limits. In practice, most specifications fall into one of three tiers:

• 90°F to 95°F: Standard commercial and residential work. This is the most common specification limit and covers the majority of projects.
• 80°F to 85°F: Bridge decks, elevated slabs, and structural elements where long-term durability is critical. DOT specifications often use this range.
• 70°F to 75°F: Mass concrete elements, post-tensioned slabs, and high-performance concrete applications. Meeting this limit in summer typically requires liquid nitrogen cooling or ice replacement of mix water.

When the specification says “concrete temperature at placement shall not exceed 90°F,” that means the temperature measured in the concrete as it comes out of the truck or pump - not the air temperature and not the temperature when it was batched. Concrete can gain 2°F to 5°F during transit in hot weather, so your batch temperature needs to be well below the specification limit.

Preconstruction Planning Under ACI 305

ACI 305 emphasizes preconstruction planning as the single most important factor in successful hot weather concreting. This means:

Mock-up pours: For critical elements or first-time hot weather work, place a test section using the actual mix, crew, and equipment planned for production. Evaluate workability, set time, finishing characteristics, and curing effectiveness. Fix problems on the mock-up, not on the production pour.

Contingency plans: Document what happens when conditions exceed your plan. What if the concrete arrives at 92°F when the specification says 90°F? What if a truck is delayed 30 minutes? What if wind picks up unexpectedly? Having written contingency plans prevents field-level panic decisions.

Supplier coordination: Meet with your ready-mix supplier before hot weather season starts. Discuss target temperatures, available cooling methods, retarder dosages, and delivery scheduling. The supplier needs lead time to source ice, adjust plant operations, and schedule drivers for early morning or night pours.

Monitoring and Testing Frequency

ACI 305 recommends increased testing frequency during hot weather conditions. Standard practice for hot weather pours includes:

• Temperature checks on every truck (not every third or fourth truck)
• Slump testing at point of placement, not at the truck discharge
• Air content testing at increased frequency (every 25 to 50 CY instead of every 50 to 100 CY)
• Evaporation rate calculation at least once per hour, or whenever conditions change noticeably

Recording all of this data is essential. Contractors using digital daily logs can capture temperature readings, test results, and weather conditions in real time, creating a defensible record that holds up if questions arise about concrete quality months later.

When to Stop Pouring

ACI 305 does not give a simple “stop pouring at X degrees” rule. Instead, it says to stop when conditions make it impossible to place, consolidate, and finish concrete to specification quality. In practical terms, stop or delay the pour when:

• Concrete temperature at the truck exceeds the specification limit and cannot be brought down
• Evaporation rate exceeds 0.25 lb/ft2/hour and you do not have adequate evaporation control measures in place
• Set time is so accelerated that the finishing crew cannot keep up with the placement rate
• Wind speed exceeds 15 mph and windbreaks are not available

Walking away from a pour is painful and expensive. But placing concrete that fails to meet specifications is more expensive. The cost of a delayed pour is measured in thousands. The cost of a failed pour is measured in tens of thousands or more.

Admixture Selection for Hot Weather Pours

Admixtures are the concrete contractor’s best tools for managing hot weather conditions. Choosing the right admixture - and the right dosage - makes the difference between a successful pour and a disaster.

Retarding Admixtures (ASTM C494 Type B and D)

Retarders slow the hydration of cement, extending set time and workability. In hot weather, they are nearly universal.

Type B (retarding only): Delays initial set by 1 to 3 hours depending on dosage and temperature. Used when the primary concern is extending the working window for placement and finishing.

Type D (water-reducing and retarding): Provides both set retardation and water reduction (5% to 10%). This is the most common choice for hot weather because it addresses two problems simultaneously: faster set times and increased water demand.

Dosage considerations:

• Standard dosage rates are calibrated for moderate temperatures (65°F to 75°F). In hot weather, you may need to increase the dosage by 25% to 50% to achieve the same retardation effect.
• Over-retardation is a real risk. If you double the dosage on a day that turns out cooler than expected, the concrete may not set for 12 to 24 hours, delaying finishing and protection.
• Work with your admixture supplier to develop temperature-based dosage charts. Knowing the exact dosage for 85°F versus 95°F versus 105°F ambient conditions eliminates guesswork.

Water-Reducing Admixtures (ASTM C494 Type A and F)

Water reducers allow you to achieve target slump with less water, keeping the water-to-cement ratio low even when hot concrete demands more fluidity.

Mid-range water reducers (Type A): Reduce water by 5% to 12%. Good for moderate hot weather conditions where the concrete arrives slightly stiffer than expected.

High-range water reducers/superplasticizers (Type F): Reduce water by 12% to 30%. Essential for hot weather pours where concrete arrives with significant slump loss. A dose of superplasticizer at the job site can restore 4 to 6 inches of slump without adding a drop of water.

Job-site addition of superplasticizer: Many contractors keep superplasticizer on site during hot weather pours. When a truck arrives with lower slump than expected, a measured dose added to the truck drum and mixed for 2 to 3 minutes restores workability. This is far better than adding water, which permanently damages the mix.

Hydration-Stabilizing Admixtures

These specialty admixtures essentially pause hydration for a set period, then allow it to resume normally. They are particularly useful for:

• Long haul distances where transit time exceeds 60 minutes
• Situations where trucks may sit on site waiting for pump availability
• Large pours where the last trucks arrive hours after the first

Stabilizers can hold concrete in a workable state for 2 to 5 hours depending on the product and dosage. They are more expensive than standard retarders ($8 to $15 per cubic yard) but provide a level of schedule insurance that retarders cannot match.

Shrinkage-Reducing Admixtures (SRAs)

SRAs reduce drying shrinkage by lowering the surface tension of pore water in the concrete. In hot weather, where rapid moisture loss amplifies shrinkage forces, SRAs provide an additional layer of protection against cracking.

They do not replace proper curing, but they reduce the consequences of imperfect curing - which is valuable given how difficult it is to maintain perfect curing conditions in 100°F heat.

Fiber Reinforcement as a Supplement

While not technically an admixture, synthetic microfibers (typically polypropylene at 1.0 to 1.5 lb per cubic yard) are commonly added to hot weather mixes to reduce plastic shrinkage cracking. The fibers bridge developing cracks while the concrete is still in a plastic state, preventing them from propagating.

Fibers are not a substitute for proper evaporation control and curing. They are insurance - a secondary line of defense when conditions are aggressive.

Curing Methods Comparison for Hot Weather

Curing is critical in any condition, but hot weather magnifies the consequences of poor curing exponentially. Here is a detailed comparison of curing methods specifically for hot weather performance.

Liquid Curing Compounds

How they work: Spray-applied membranes that form a film on the concrete surface, trapping moisture inside.

Hot weather performance: Good for most applications. The main risk is application timing - in hot weather, the surface may dry enough to prevent good adhesion if you wait too long after finishing. Apply within minutes of final trowel pass.

Pros:

• Fast application over large areas
• No ongoing maintenance required
• Cost-effective ($0.02 to $0.05 per square foot)
• Does not interfere with subsequent construction activities

Cons:

• One-time application - if the membrane is damaged or incomplete, moisture escapes permanently
• Efficiency varies (most compounds retain 75% to 90% of moisture versus perfect wet curing)
• Some compounds interfere with adhesion of floor coverings, coatings, or toppings
• In extreme heat (100°F+), single application may not provide adequate moisture retention

Best practice for hot weather: Apply two coats in perpendicular directions at the full recommended rate. The second coat catches any gaps or thin spots from the first.

Wet Burlap Curing

How it works: Saturated burlap sheets placed directly on the finished concrete surface, kept continuously wet.

Hot weather performance: Excellent - this is the gold standard. Wet burlap not only prevents moisture loss but actively cools the concrete surface through evaporation, reducing the temperature differential between surface and interior.

Pros:

• Most effective curing method available
• Cools the surface, reducing thermal stress
• Maintains near-100% humidity at the concrete surface
• Can be reused across multiple pours

Cons:

• Labor-intensive to place and maintain
• Must stay wet continuously - dry burlap actively wicks moisture out of concrete (worse than no curing at all)
• In extreme heat, burlap may need re-wetting every 30 to 60 minutes
• Requires water supply on site throughout the curing period

Best practice for hot weather: Cover burlap with white plastic sheeting to reflect solar radiation and reduce the rate of evaporation from the burlap. This combination dramatically reduces re-wetting frequency.

Ponding or Immersion

How it works: The concrete surface is flooded with water contained by temporary dams.

Hot weather performance: Outstanding. Ponding provides unlimited moisture and significant cooling. A 2-inch layer of water on the surface keeps concrete temperature well below ambient air temperature.

Pros:

• Most effective cooling and moisture retention
• Virtually eliminates any risk of surface drying
• Simple concept with minimal materials

Cons:

• Only works on flat, level surfaces
• Requires containment dams and continuous water supply
• Cannot be used on vertical or sloped surfaces
• Water must be within 20°F of concrete temperature to avoid thermal shock

Best practice for hot weather: Start ponding as soon as the surface is hard enough to resist erosion. Use water that is not drastically colder than the concrete - a sudden cold water application on hot concrete creates thermal stress at the surface.

Plastic Sheeting

How it works: Polyethylene sheets (typically 4 to 6 mil) placed directly on the concrete surface after finishing.

Hot weather performance: Moderate to good. Effective at trapping moisture but does nothing to cool the surface. Under direct sun, the air space beneath clear plastic can actually exceed ambient temperature, accelerating the curing reaction unevenly.

Pros:

• Inexpensive and widely available
• Easy to install
• Good moisture retention when properly sealed at edges

Cons:

• Can cause discoloration (mottled light and dark patches) where sheet is not in full contact
• Clear plastic under direct sun creates greenhouse effect
• White plastic is better but still traps heat
• Must be sealed at edges and seams to prevent wind from lifting

Best practice for hot weather: Use white or opaque plastic to reflect solar radiation. Weight edges and seams thoroughly - wind getting under the plastic defeats the purpose entirely.

Comparison Summary

For critical concrete work in extreme heat, wet burlap covered with white plastic is the recommended approach. For standard commercial flatwork, two coats of curing compound applied immediately after finishing is adequate for most conditions below 95°F.

Scheduling Concrete Pours Around Weather

Weather does not wait for your schedule, but smart scheduling can work around the worst conditions. Contractors who consistently produce quality concrete in hot climates treat weather as a scheduling variable, not an afterthought.

Building Weather Into Your Project Schedule

The biggest scheduling mistake contractors make is treating every pour day the same regardless of season. A pour that takes 4 hours in October may take 6 hours in July because of early morning starts, slower finishing in pre-dawn darkness, and additional curing setup time.

When building your project schedule, account for these hot weather factors:

Earlier start times: Hot weather pours typically start 2 to 3 hours earlier than moderate-weather pours. This means concrete trucks need to be scheduled for 4:00 or 5:00 AM delivery, which requires coordination with the batch plant’s operating hours.

Longer curing periods: If your schedule assumes 3-day cure times for form stripping, hot weather mixes with SCMs may need 5 to 7 days. Build this into the critical path.

Weather hold days: In regions with extreme summer heat (Phoenix, Las Vegas, Dallas, Houston), experienced contractors build 1 to 2 weather hold days per week into the schedule during peak summer months. Using construction scheduling software to manage these contingency windows keeps the project on track even when individual pour days shift.

Crew rotation: Night pours require different crew scheduling. If your team is working 4:00 AM starts, they cannot also work afternoon tasks. Plan crew assignments around pour schedules, not the other way around.

Using Weather Forecasts Effectively

A 10-day forecast is useful for planning. A 48-hour forecast is what you actually use for go/no-go decisions.

72 hours before the pour: Check the extended forecast. If extreme heat is predicted, confirm ice and chilled water availability with your supplier. Alert finishing crews about the early start time.

24 hours before the pour: Make the go/no-go decision based on the detailed forecast. Check predicted temperature, humidity, and wind speed for the specific hours of your pour. Calculate the expected evaporation rate. If conditions will be marginal, prepare contingency measures.

Morning of the pour: Check actual conditions against the forecast. Measure air temperature, humidity, and wind speed on site. Calculate the real evaporation rate. If conditions are significantly worse than forecast, you still have time to delay or add precautions.

Coordinating With Your Ready-Mix Supplier

Your supplier needs advance notice for hot weather pours, especially if cooling measures are required.

Ice orders: Batch plants do not keep unlimited ice on hand. Order 48 to 72 hours in advance for pours requiring ice-cooled concrete. For large pours (100+ CY), confirm the supplier’s ice-making or delivery capacity.

Delivery spacing: In hot weather, you want trucks arriving every 8 to 12 minutes for continuous placement. Gaps longer than 15 to 20 minutes risk cold joints. Coordinate your delivery schedule based on your placement rate and have backup trucks staged for delays.

Plant start time: If your first truck needs to arrive at 5:00 AM, the batch plant needs to be operating by 4:15 AM. Not all plants run pre-dawn shifts during the week, and weekend availability may be limited. Confirm operating hours early in the planning process.

Tracking and Documenting Weather Decisions

Every pour should have a weather record, but hot weather pours demand detailed documentation of why decisions were made. When you decide to pour at 4:00 AM instead of 7:00 AM, or delay a pour by one day due to extreme heat, record the reasoning.

This documentation serves multiple purposes:

• Protects you in disputes about schedule delays caused by weather
• Creates a historical record for estimating future hot weather projects
• Demonstrates due diligence if concrete quality questions arise later

Contractors using digital daily log tools can attach weather data, temperature readings, and photos directly to each pour record, creating a complete history that paper logs cannot match. When a project owner questions why a pour was delayed, pulling up the weather data and evaporation rate calculations from that specific day ends the conversation.

Seasonal Pour Planning

Experienced concrete contractors in hot climates plan their annual schedules to front-load the most critical or temperature-sensitive pours into cooler months. Mass concrete elements, post-tensioned slabs, and architectural concrete go into the schedule for October through April when possible. Standard flatwork and non-critical pours fill the summer months.

This is not always possible - project timelines do not always allow seasonal optimization. But when you have scheduling flexibility, using it to avoid placing critical concrete during the most extreme heat saves time, money, and risk. Project scheduling tools that give you a clear view of all upcoming pours across multiple projects make this kind of strategic planning practical rather than theoretical.

Putting It All Together

Hot weather concreting comes down to four principles:

1. Keep the concrete cool. Lower the temperature before it arrives on site. Do not rely on job-site measures to compensate for hot concrete.

2. Keep the concrete wet. Control evaporation from placement through the end of curing. Every square foot of exposed surface is losing moisture every second.

3. Work fast. The window for proper placement, consolidation, and finishing is compressed. Plan accordingly and crew up.

4. Cure aggressively. Start curing immediately and maintain it for at least 7 days. Shortcuts in curing are the leading cause of surface failures in hot weather.

None of this is complicated. It just requires planning, coordination with your ready-mix supplier, and discipline from your field crew. The contractors who pour great concrete in 100-degree heat are not doing anything secret. They are doing the basics, consistently, every time.