Concrete is one of the most versatile and widely used construction materials on earth. It’s strong, durable, low maintenance, fire resistant, simple to use, and can be made to fit any size or shape, from unfathomably massive structures to humble stepping stones.
Yet, whether you're a concrete contractor or a homeowner wanting to pour your own concrete slab, you know that getting concrete poured, set, and cured can be a more difficult process than many think.
Here at Gra-Rock, we've been in the ready-mix concrete business for years, and we understand the frustration of working with concrete in different weather conditions. While concrete is fairly simple to pour, its durability and longevity are often dependent on heat, cold, humidity, or rain.
If you are planning a concrete pour or have experienced unsatisfactory results from other concrete pours, this article is for you! We’ll give you tips and tricks for pouring concrete in any weather and help you understand how concrete works so you can become a pouring concrete.
Ready to dive in? Let’s get started!
How Concrete Sets and Cures
Before we get into practical tips for pouring concrete in any weather, let’s make sure we have a clear understanding of what concrete is and how it works.
First of all, concrete is not cement! Cement, which is crushed limestone and clay heated to high temperatures in a kiln, is just one of the key ingredients in concrete. To make concrete, you need a combination of the following:
Sand (fine aggregate)
Gravel (coarse aggregate)
(If you want to know more about concrete, read our Beginner's Guide to Ready-Mix Concrete.)
If you’ve ever used a bag of ready-mix concrete, you’ve received the first three ingredients already measured and mixed, and your job is simply to add the last ingredient: water. When you do that, voila! You have concrete that can be used in a myriad of applications.
Understanding concrete’s relationship with water is extremely important in mastering the art of pouring concrete in inclement weather.
Concrete does not actually “dry” as the water evaporates. Instead, concrete sets and cures through a chemical reaction called hydration. The water actually becomes an essential part of the cured concrete.
But wait—what’s actually happening in the chemical reaction of hydration?
What is Hydration?
When the chemical properties of cement interact with water, compounds like tobermorite gel and calcium hydroxide begin forming on the outside of the cement particles. The growth on the outside of the cement particles results in a strong, interlocking rod structure.
Although the primary work of hydration happens within 5 hours of contact with water, the process of hydration will continue slowly for a very long time.
This is why you shouldn’t let the concrete dry out while it's curing. Lack of water can prematurely stop the hydration process keeping the concrete from reaching its full strength. In fact, as long as you avoid washing out the cement, concrete can be placed and cured completely underwater!
How the Weather Affects Concrete
This sheds some light on why weather can affect the strength of concrete. If the concrete sets and cures too quickly due to heat, low humidity, wind, or cold, the strength of the concrete is compromised.
This doesn’t mean that more water is always better in pouring concrete. Extra water often causes even bigger problems than a water deficit.
When there is too much water in your concrete mix, the chemical bonds will be separated from each other by large areas of water. This reduces the strength of cured concrete.
More water results in increased porosity, meaning that the hardened concrete will have many canals, which can affect any color or finish that may be applied to the surface.
Once cured, concrete with too much water will also have a much greater risk of shrinkage and cracks, especially in freeze-and-thaw climates, meaning that it will be particularly weak.
Pro tip: If you want to ensure that your concrete has the proper ratio of cement, aggregate, and water, contact your local ready-mix concrete supplier!
It’s likely they have a mix that fit your needs, and the concrete will be delivered straight to you, making the whole process much less of a headache.
But now that we understand how concrete works, let's look into how different weather affects concrete.
Pouring Concrete in Cold Weather
The first question to ask about pouring concrete in cold weather is, “How cold is too cold?”
The American Concrete Institute defines that concrete will be exposed to cold weather when the following conditions exist:
The average daily temperature is less than 40 degrees Fahrenheit (5 Celsius)
The air temperature is not greater than 50 degrees Fahrenheit (10 Celsius) for more than 12 of the 24-day hours.
If you are pouring concrete in conditions cooler than those listed above, you should take extra precautions to make sure your concrete will set and cure properly.
Here are a few tips to ensure you have a successful pour:
Prepare the pour site by removing any snow or ice, ice, or standing from the work area. Never pour concrete over frozen ground!
Start your pour in the early morning so the concrete can soak up the full effect of the afternoon sun while it is still setting.
Use a low slump and minimal water-to-cement ratio. This will reduce water bleeding and the set time, which allows less time for the water in the concrete to freeze.
Use a product to speed up the set time of the concrete, like SpeedSet or calcium chloride.
Use concrete curing blankets to prevent freezing and keep the concrete at an optimal curing temperature. Make sure to keep the concrete from freezing for a minimum of 3 days. You can use these same products to protect the ground from freezing that you will pour the concrete on.
The temperature of any items to be embedded in the concrete (rebar, wire mesh, etc.) needs to be above freezing before coming into contact with fresh concrete.
Do not begin final finishing operations while bleed water is present.
Request a heated mix from your concrete supplier.
Set up a heated enclosure. If combustion heaters are used, remember to vent outside to prevent carbonation!
Use a waterproofing concrete sealer as a curing compound instead of water curing.
Once the concrete is hard, don’t use any de-icing salts. These corrode the surface and allow water to permeate, freeze, and eventually crack your fine work.
By following these tips when pouring concrete in cold weather, you will ensure a quality pour!
Pouring Concrete in Hot Weather
So, if you live in a climate that doesn’t experience cold or freezing temperatures, you can safely pour concrete all year long, right?
Remember, hydration is the most important aspect of achieving strong, durable concrete. Hot temperatures cause concrete to have a deficit of water and not be set correctly.
When the summer months get really hot, it can be a little too much of a good thing. In fact, concrete cures best in a range between 70° to 80° F. As your temperature approaches 90° F, however, you’ll start to run into problems.
“Hot weather” is more than just temperature. Days of low relative humidity, as well as days with high wind speeds, also are grouped into “hot weather.”
Remember that maintaining an appropriate level of moisture in the concrete is the highest priority. Warm temperatures, low humidity, and high wind speeds increase the rate of evaporation, making it more challenging to retain moisture in the concrete.
If outdoor temperatures are nearing 90 degrees Fahrenheit, or if the day is dry and windy, you should take precautions to ensure a good concrete pour.
Here are a few tips to ensure a good concrete pour in hot weather:
Use a large size and amount of coarse aggregate particles if hot weather is likely to occur during the concrete placement. Larger aggregates will minimize the probability of having concrete shrink due to environmental conditions.
If possible, avoid pouring concrete at noon or during the afternoon.
Consider using hot weather admixtures like recycled plastic additives. This will make your mix easier to work with and increase its setting time so it can cure to greater strength.
Request chilled water from your concrete supplier, or if mixing your own concrete use an industrial chiller.
Use sunshades or windbreaks to reduce possible harsh conditions.
Once water has been added to the mix, reduce your mixing time. Over-mixing will create more water loss through evaporation.
All necessary equipment should remain covered until the last moment before use. Keep chutes, conveyors, and accessories under a roof if possible and spray some water over them regularly.
When placing concrete for a slab, first dampen the subgrade.
Use cool water to dampen side forms for slabs or walls.
Call for all hands on deck. Due to faster set times, you will need as much manpower as possible to get the job done quickly.
Pouring concrete in the summer heat can be challenging for both our bodies and the concrete! Using the tips and tricks listed above will help concrete set and cure properly and ensure that you feel great about the job you did!
Pouring Concrete in Rainy Weather
Pouring concrete in the rain may be the biggest challenge you face in regard to getting a great result.
If possible, simply avoid pouring concrete in the rain! You will definitely want to steer clear of torrential rain or prolonged periods of rain.
However, if you experience a long period of damp weather and you’re facing a project deadline, or if you just get stuck in an unexpected downpour, here are a few steps you can take to help your cause:
Make sure you have a great drainage system. This ensures that no rainwater will pool in trenches dug for footers, foundations, and slabs.
If possible, tent the pour with tarps to keep rain from mixing with the concrete. The more water that mixes with semi-solid concrete, the more likely it is to fail.
Don’t work the rainwater into the concrete surface!
Don’t soak up rainwater with dry cement. This will impair the finish and further weaken the top layer of concrete.
Once the rain passes, use a float to push the water off the edge of the slab before you start finishing.
Sometimes the weather makes it difficult to create a perfect concrete pour, which is why it's best to be informed about how to pour concrete in all weather conditions.
But beyond that, it's also a good idea to focus on the elements you can control, such as finding a ready-mix concrete supplier you can trust.
At Gra-Rock, we deliver quality ready-mix concrete, and we do our best to be stable and reliable.
Whether it's our proven mixes and designs, our guaranteed delivery, or our helpful team of truck drivers, we aim to ensure that you will be happy and confident in your concrete.
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Can you pour concrete in any weather? ›
Temperatures for Pouring Concrete
Elements like volume changes, cracking, humidity, wind speed, and temperature all should be accounted for when pouring concrete. Experts agree that the best temperature for pouring concrete is between 40 °F and 60 °F.
In no case should concrete be allowed to freeze during the first 24 hours after it has been placed. Since cement hydration is an exothermic reaction, the concrete mixture produces some heat on its own.Can you pour concrete in 20 degree weather? ›
Experts agree that the best temperature to pour concrete is between 50-60 °F. The necessary chemical reactions that set and strengthen concrete slow significantly below 50 °F and are almost non-existent below 40 °F.Is it OK if it rains while pouring concrete? ›
Surprisingly, yes, you can pour concrete in the rain. Concrete does not dry, it cures. Curing is a chemical reaction and not a physical one, so rainwater won't kill concrete. Considering concrete can be cast and cured underwater, some rain on your property won't normally harm a job.Can you pour concrete in 25 degree weather? ›
Concrete has many phases and each one is important. The phase in which concrete is moist is known as the plastic phase. During this phase it is crucial to control the temperature of the concrete. If outdoor temperatures fall below 25 degrees Fahrenheit the concrete will most likely freeze.Can you pour concrete if it freezes at night? ›
For it to set correctly, you must protect fresh concrete from freezing during the first 24 hours. If it freezes, it will lose much of its strength. However, with proper safety measures and planning, you can pour concrete successfully even in cold weather conditions.When should I start watering my concrete? ›
Many construction specialists recommend watering it down five to ten times per day, for the first week, starting 2-4 hours after it has been poured. The first two to four hours lets the concrete “finish”, which refers to the setting process.How long does 4 inches of concrete take to cure? ›
How long does four to six inches of concrete take to cure? As stated previously, concrete takes approximately 26-30 days to reach its full strength. If the concrete is professionally poured and floated, the curing process should be sound and ensure proper hardening of the concrete base.Should you spray water on new concrete? ›
Properly curing your concrete improves strength, durability, water tightness, and resistance for many years. The first 7 days after installation you should spray the slab with water 5-10 times per day, or as often as possible. Once the concrete is poured the curing process begins immediately.At what temperature will concrete not set? ›
What Temperature Is Too Cold to Pour Concrete. Concrete sets and forms best between 50 and 60 degrees Fahrenheit. Concrete will cure at 30 degrees, and if the air temperature is between 30 and 40 degrees, you'll want to make sure your mixed concrete maintains a temperature of between 55 and 60 degrees.
What is the minimum temp for pouring concrete? ›
In order to avoid these issues, it's advised to pour concrete at a temperature between 50 to 60°F. Temperatures below 50°F will begin to slow the curing process, and the water in the cement is at risk of freezing at temperatures below 40°F.At what temperature does concrete fail? ›
The threshold of significant degradation of concrete is around 65-93°C (150-200°F). For this reason, current codes and industry standards dealing with reinforced concrete structures specify a maximum temperature limit of about 65-93°C (15O-2OO°F) to ensure predictable concrete behavior.What is the best month to pour concrete? ›
Considering all the factors listed above, the best months for pouring concrete would be June, September, and early October. During these months, the weather will be mild and dry. Therefore, the concrete will set properly.What's the lowest temperature you can pour concrete? ›
In order to avoid these issues, it's advised to pour concrete at a temperature between 50 to 60°F. Temperatures below 50°F will begin to slow the curing process, and the water in the cement is at risk of freezing at temperatures below 40°F.Will concrete cure at 40 degrees? ›
Concrete sets more slowly when it is cold—very slow below 50 degrees Fahrenheit and below 40 degrees Fahrenheit, the hydration reaction basically stops and the concrete doesn't gain strength. Anything below 40 degrees Fahrenheit will slow the curing process and may even stop it altogether.What time of day is best to pour concrete? ›
For example, if you're pouring concrete in Arizona in the summer, you're going to want to do it in the early morning or evening before the heat of the day to avoid setting complications. It's worth mentioning that it's possible to pour concrete at any time of the year.