Everyone's Guide To Pouring Concrete In Any Weather

Concrete is one of Earth's most versatile and widely used construction materials. It’s strong, durable, low maintenance, fire resistant, simple to use, and can be made to fit any size or shape, from massive skyscrapers 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.

Why?

The weather.

Here at Gra-Rock, we've been in the ready-mix concrete business for years, and we understand the frustration that comes with working with concrete in various weather conditions. While concrete is fairly simple to pour, its durability and longevity are often dependent on factors such as heat, cold, humidity, or rain.

If you are planning a concrete pour or have experienced unsatisfactory results from previous 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 pro at pouring concrete.

Ready to dive in? Let’s get started!

No time to read? Here's a TL:DR

• The blog post offers a guide for pouring concrete in various weather conditions, emphasizing that a successful outcome depends on managing factors such as heat, cold, humidity, and rain.

• For cold weather (below 40°F), tips include removing snow and ice, pouring early in the day, and using curing blankets to prevent the concrete from freezing.

• For hot weather, the article recommends using larger aggregates, pouring the concrete in the morning or evening, and using sunshades to protect it.

• For rainy weather, the primary recommendation is to avoid pouring if possible. If necessary, ensure good drainage and use tarps to prevent excess water from mixing with the concrete.

Interested in learning more? Keep reading below!

How Concrete Sets and Cures

Before we delve into practical tips for pouring concrete in any weather, let’s ensure we have a clear understanding of what concrete is and how it works.

First of all, concrete is not just cement! However, cement, which is crushed limestone and clay heated to high temperatures in a kiln, is one of the key ingredients in concrete. To make concrete, you need a combination of the following:

• Cement

• Sand (fine aggregate)

• Gravel (coarse aggregate)

• Water

(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 already received the first three ingredients, which are measured and mixed. Your job is to add the last ingredient: water. Mix, and voila! You have concrete you can use for any small project.

Understanding the relationship between concrete and water is crucial in mastering the art of pouring concrete in inclement weather.

It's a common misconception that concrete "dries." 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. You don't want all the water to evaporate from your pour, or you've got problems!

But wait—what’s actually happening in the chemical reaction of hydration?

What is Hydration?

When cement's chemical properties interact with water, compounds such as tobermorite gel and calcium hydroxide begin to form on the surface of the cement particles. This growth results in a strong, interlocking rod structure.

Although the primary work of hydration occurs within 5 hours of contact with water, the hydration process will continue slowly for a very long time.

This is why you shouldn’t let the concrete dry out while it's curing. A lack of water can prematurely halt the hydration process, preventing the concrete from reaching its full strength. In fact, as long as you avoid washing out the cement, concrete can be successfully placed and cured completely underwater!

How the Weather Affects Concrete

This doesn’t mean that more water is always better when pouring concrete. Extra water creates even bigger problems than water deficiency.

When there is too much water in your concrete mix, the chemical bonds between the particles will be separated by large areas of water. This also 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 excessive water will also be more prone to shrinkage and cracking, especially in freeze-thaw climates, making it particularly weak.

Pro tip: Contact your local ready-mix concrete supplier to ensure that your concrete has the proper ratio of cement, aggregate, and water!

They likely have a mix that fits your needs, and the concrete will be delivered straight to you, making the whole process much less of a headache.

Now that we understand how concrete works, let's examine how different weather conditions affect concrete.

Pouring Concrete in Cold Weather

The first question to ask about pouring concrete in cold weather is, “How cold is too cold?”

Here's how the American Concrete Institute defines cold weather:

• The average daily temperature is less than 40° Fahrenheit (5° Celsius)

• The air temperature is not greater than 50°F (10 °C) for more than 12 of the 24-hour days.

If you are pouring concrete in conditions cooler than those listed above, you should take extra precautions to ensure your concrete sets and cures properly.

Here are a few tips to ensure you have a successful pour in cold weather:

• Remove snow and ice from the work area to prepare the pour site for construction. Never pour concrete over frozen ground!

• Start your pour in the early morning so the concrete can absorb the full sun's effect throughout the day.

• Use a low slump and a 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 setting time of the concrete, such as SpeedSet or calcium chloride.

• Use concrete curing blankets to prevent freezing and keep the concrete at an optimal curing temperature. Ensure that the concrete is kept from freezing for a minimum of 3 days. You can use these same products to protect the ground from freezing on which the concrete will be poured.

• The temperature of any items to be embedded in the concrete (such as rebar or wire mesh) must 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 them outside to prevent carbon monoxide poisoning.

• Use a waterproofing concrete sealer as a curing compound instead of water curing.

• Once the concrete is hardened, refrain from using de-icing salts. These corrode the surface, allowing water to permeate, freeze, and eventually crack your fine work.

By following these tips when pouring concrete in cold weather, you up your chances of 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?

Wrong.

Remember, hydration is the most critical aspect of achieving strong, durable concrete. Hot temperatures cause concrete to have a water deficit and prevent it from setting correctly.

Concrete cures best in a range between 70° F and 80° F. So, while higher temperatures are nice, you’ll start running into problems as they approach 90° F.

These issues are most severe on days with low relative humidity and high wind speeds.

Remember, maintaining an appropriate level of moisture in the concrete is paramount. 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°F or if the day is hot, dry, and windy, take precautions to correct for the high temperatures.

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 shrinkage due to environmental conditions.

• If possible, avoid pouring concrete during the noon hour or the afternoon.

• Consider using hot weather admixtures, such as recycled plastic additives, to enhance the durability of your concrete. This will make your mix easier to work with and increase its setting time, allowing it to cure to a 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 the risk of harsh conditions.

• Once water has been added to the mix, reduce your mixing time. Over-mixing will result in increased water loss through evaporation.

• All necessary equipment should remain covered until the last moment before use. If possible, keep chutes, conveyors, and accessories under a roof 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 the concrete set and cure properly, ensuring that you feel great about the job you did.

NOTE: Make sure to have plenty of liquid on hand for your crew, too! Pouring concrete in hot weather is hard work.

Pouring Concrete in Rainy Weather

Probably the biggest challenge you'll face when pouring concrete is rain.

Whenever possible, avoid pouring concrete in the rain! Rain causes all sorts of issues. If there is torrential rain or prolonged periods of rain, reschedule the project for another day.

However, if you experience a long period of damp weather and you’re facing a project deadline, or if you get stuck in an unexpected downpour, here are a few steps you can take to help your cause:

• Ensure you have an effective drainage system. This ensures that rainwater does not 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 let rainwater soak into 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.

Conclusion

Sometimes, the weather makes concrete pouring difficult. That's why it's best to be informed about how to pour concrete in all weather conditions. Focus on the elements you can control, such as finding a reliable ready-mix concrete supplier.

At Gra-Rock, we deliver quality ready-mix concrete and strive to be a stable and reliable provider.

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.

We offer educational resources, including:

- Pouring Concrete In Hard-to-Reach Places

- Understanding Concrete Strength: From PSI To Tips For Pouring Concrete

- Concrete Rebar: Everything You Need To Know [plus 8 Main Types]

Contact us today to get the concrete you need and the customer service you deserve!