What Are Concrete Blankets?

Concrete curing blankets keep the concrete warm as it dries and cures. When temperatures drop below 40 degrees Fahrenheit, water inside the concrete mixture can freeze and cause structural damage. During the curing process concrete warms up from the inside. Concrete blankets lock heat in while keeping the cold out. They prevent water from freezing which allows curing to occur. This is why they’re also called curing blankets. Most are just thick insulated blankets, but some designs have electric heaters built in, which can keep concrete warm when insulation alone isn’t enough.

Concrete is made by mixing sand, cement and stone with water. Cement is the active ingredient that chemically reacts with water to harden and strengthen over time. This is called curing and takes around 28 days to complete.

As curing occurs, concrete dries out and grows increasingly stronger. But for this too happen it can’t be too cold or the water will freeze, which can crack or deteriorate the slab. Concrete blankets prevent this from happening.

If small cracks form in your concrete, fill them immediately with a concrete crack filler to prevent them from getting worse.

I’ve been a mason for over 25 years and have seen concrete slabs completely destroyed because they froze before curing strong enough to resist freezing on their own. When pouring concrete in cold weather, curing blankets are essential.

Blankets are applied after the concrete is pumped in place, spread out, and worked with a concrete tamper, screeds, floats, shaping tools, sponges, and trowels. They’re the last step that protects your slab so it can cure properly in cold weather.

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Why Are Concrete Blankets Needed

Temperature has a big impact on concrete as it cures. In warm climates, a concrete blanket isn’t needed because the temperature required for curing is already correct. But what about here in the Northeast where it routinely gets below freezing or in states like Alaska that are almost always too cold for concrete work. Not only are the working conditions cold, but the concrete mixture itself can freeze. To prevent this from happening concrete blankets are used to cover the concrete and keep it warm.

Approximately 15 to 20% of a concrete mixture is water. During the curing process, much of that water is slowly evaporated out as the concrete strengthens. When concrete freezes, its strength is drastically reduced. Water inside the concrete expands as it freezes which destroys the internal structure of the concrete. Water can expand 10 percent in volume when it freezes. This breaks internal bonds and causes the concrete to be flaky and weak. In some extreme cases the concrete can even deteriorate and turn back to powder.

Freezing should be avoided for at least the first few days after the concrete is poured. More importantly, it should be prevented during the first few hours when the concrete mixture is still wet. The more water there is in the concrete the more damage can occur after a freeze.

How To Use A Concrete Blanket

Using a concrete blanket is very simple to do. You just lay them right on top of the concrete. But there’s a few things to consider when selecting the right blanket.

The first thing you should do is assess the temperature of the ground and the weather. Try to pour on a warm day and at a time of day when the temperature is it’s warmest. The air temperature is easy to figure out but for the ground we use a temperature gun. Just point it at the ground and it will tell you it’s temperature. For some concrete jobs in extreme cold you may have to warm the ground up first. Electric powered concrete blankets are great for this. Just lay them on the surface and plug them in, the blankets will do all the work.

Next you need to figure out how much insulation is needed. Usually a single blanket is enough but for some jobs heated electric blankets or multiple layers may be needed.

We almost always use more blankets around the edges and corners. This is where most of your heat loss will occur because it’s next to earth. You can either get thicker blankets or stack them on top of each other.

Curing blankets come in a variety of sizes. Make sure you have enough to cover the entire surface. Watch your seams. When you pay out the blankets all the concrete should be covered. It’s easy to miss a seam here or there so lay them carefully. If there’s even a small area of exposed concrete heat will escape.

Curing Blankets Lock In Moisture

Not only do concrete blankets help maintain a temperature above 40 degrees, but they also lock in moisture. Moisture is a very important part of the curing process. It’s needed to prevent cracks and rapid drying. Working with concrete in extremely hot and dry weather is just as challenging as in the cold.

When it’s hot, masons will spray water on the concrete’s surface to keep it moist. The concrete needs to dry out, but it has to be done slowly. Rapid drying isn’t as bad as freezing but it’s still a big problem. In cold climates, you can actually have both problems happening at the same time. Many cold climates are also very dry. When water evaporates from the surface it can freeze as soon as it hits the air. So how do you keep the concrete’s surface moist? With a concrete blanket.

Curing blankets not only prevent freezing but also lock in moisture where you want it. As the concrete evaporates, moisture it’s locked in by the blanket and kept on the surface.

Concrete Blankets Are Waterproof

Another common feature of concrete blankets is that they’re waterproof. The outer covering is made from a tough material called polyethylene. It feels just like a heavy weight tarp.

The inside is made from polypropylene foam insulation which is also waterproof. If water should get through the outer shell it won’t penetrate through the internal foam.

Controlling moisture is a very important part of curing concrete. Moisture you don’t want has to be kept out while moisture you do want is kept in. A waterproof vapor barrier is a great way to do it.

Insulation

Insulation reduces the heat transferred between objects. It keeps warm concrete warm by preventing heat loss and keeping cold air out. This is an important concept to understand as we learn more about the different types of concrete blankets.

A concrete blanket doesn’t actually produce heat. This is also true of the blankets you use at home. Blankets make you feel warm by locking in your own warmth and keeping the cold out. They lock warmth in and keep cold out with a layer of insulation inside the blanket. The insulation is measured in what’s called an R-Value. The higher the value the better it is at insulating. In terms of a blanket, different materials and greater thicknesses will produce a more insulated blanket.

Insulation helps lock in and regulate temperatures, not increase them. For example, let’s say you put 100 F coffee in an insulated thermos. If it’s well insulated, the temperature can remain at 100 F for 8 hours or more. However, if the thermos is poorly insulated it could drop in temperature very quickly. But the temperature inside the thermos will never get hotter than 100 F unless something else heats it up. The insulation holds in and regulates the temperature inside the thermos but it doesn’t heat the coffee. The same is true of concrete blankets. A curing blanket will lock in the heat created during curing and keep cold air out, but they don’t actually heat the concrete.

Types Of Concrete Blankets

Builders have been using creative methods to keep concrete warm as it cures for centuries. In the past, bushels of straw or hay were piled on concrete once it hardened a bit and could support the weight. But these days we use insulation in the form of a blanket.

Curing blankets come in two main types.

Electric Blankets

Electric blankets work just like the kind you’d use in your own home. Rather than simply providing insulation to trap in heat and keep cold out, electric blankets actively heat the concrete below.

Electric blankets have wire coils running through them that heat up when electrified. This is in additional to their insulation. When the insulation in the blanket isn’t enough to keep the concrete warm, plug in the blanket to produce more heat.

These are often used in extremely cold temperatures where insulation isn’t enough. They can also be used when more heat is needed than the concrete can produce on it’s own. Don’t forget that in very cold climates, the ground is also quite cold. Since there’s no way to prevent the cold earth from touching your concrete and sapping it’s heat, you can add more to compensate for the heat loss by powering the blanket.

Insulation Blankets

These are typically made with a polyethylene outer shell which protects the internal polypropylene foam insulation. Both layers are water resistant and help keep the concrete dry. The other layer feels sort of like a waterproof plastic tarp with foam inside. Being water resistant not only helps keep rain and snow out but also locks moisture in at the concrete surface where you want it.

Wet Cure Blankets

Another type of concrete blanket that we rarely use is called at wet cure blanket. These are not heavily insulated and not typically used in very cold climates. But they work really well in dry ones. If your concrete is drying too quickly, you can wet it down and cover it with a wet cure blanket. The blanket will lock in moisture and prevent rapid drying.

Benefits Of Using Concrete Blankets

Concrete is effected by the environment in which you use it. The ideal temperature for pouring concrete is around 70 F. Not too dry or too humid. If it’s too humid the concrete could have issues evaporating it’s water, too dry and it could evaporate too fast. Too hot and you could get rapid drying, too cold and you’ll have freezing issues. It’s not that easy pouring concrete in the elements. But that’s where concrete blankets can help.

When the weather’s too cold, a curing blanket will keep temperatures where you need them. They’ll also keep moisture at the surface, help regulate evaporation and keep the concrete dry from outside water like rain or snow. Since almost all concrete blankets are water resistant they also double as a vapor barrier.

• Curing blankets allow concrete work to be done in cold climates.
• Come in a variety of sizes and R-Values.
• Some are heated which is great if you need more heat or are working in an extremely cold environment.
• Easy to fold up, transport and re-use.
• Can speed up the rate at which concrete cures.
• Tough and durable.
• Easy to use. All you do is lay them on top of the concrete.

Other Uses For Concrete Blankets

While curing blankets are mainly used for concrete, they can also be used in maintaining the temperature of the ground or other building materials like brick and stone.

• Pouring concrete over frozen ground or subgrade, like gravel or sand, is a bad idea. As soon as the concrete is poured, it starts rapidly cooling and can even freeze. It’s like pouring liquid into a frozen glass. It could also cause any frozen water caught within the ground to thaw and expand which can make the base uneven. If the ground is uneven it creates a weak spot where concrete can crack. Laying a concrete blanket over the ground for a few days prior to pouring can help regulate the temperature. This is even easier if the blanket is electric.
• Concrete blankets are a great way to prepare cold ground for excavation. This is especially helpful if your digging by hand. The top foot of frozen ground can be very difficult to get through even with machines.
• Brick and stone work use cement to bind materials together. The cold is just as harmful here as it is to poured concrete. Cement won’t bind brick and stone together if it’s too cold. Using a warming blanket can sometimes help.
• Preventing water from freezing is another great way to use concrete blankets. Especially if the blankets are heated. lay them over pipes or buckets of water to stop the freeze.
• A concrete blanket can also be used as a water barrier. Almost all concrete blankets are water proof. Lay them over anything you want to keep dry like bags of Quikrete.

Tips

Concrete blankets are a great way to help concrete cure in very cold weather. Here are a few more tips to help you use them.

• You can check the temperature of concrete with an infrared temperature gun. This can help you regulate it’s temperature with blankets.
• Use more of insulation at the edges and corners. Those are typically the areas where heat loss occurs the most. This is another thing you can check with a temperature gun.
• You can usually remove the blankets after 2-3 days but watch the temperature. If it’s extremely cold then keep them on. I’ll sometimes cover concrete for 7-10 days.
• Don’t use too much water in your concrete mix. This is bad under any circumstance but it’s really bad in cold weather. The extra water makes curing take longer and provides more volume to freeze.
• If you’re using powered warming blankets, make sure to have power on site for as long as you need it.
• Use the waterproof benefits of a curing blanket to keep your concrete dry.

Using concrete blankets during those first few days of curing can be a huge help and possibly the only way to pour concrete in extremely cold conditions. The curing process is essential to creating strong and durable concrete.

Summary: What Are Concrete Blankets?

Concrete curing blankets keep the concrete warm as it dries and cures. When temperatures drop below 40 degrees Fahrenheit, water inside the concrete mixture can freeze and cause structural damage. During the curing process concrete warms up from the inside. Concrete blankets lock heat in while keeping the cold out. They prevent water from freezing which allows curing to occur. This is why they’re also called curing blankets. Most are just thick insulated blankets, but some designs have electric heaters built in, which can keep concrete warm when insulation alone isn’t enough.

Concrete is made by mixing sand, cement and stone with water. Cement is the active ingredient that chemically reacts with water to harden and strengthen over time. This is called curing and takes around 28 days to complete.

As curing occurs, concrete dries out and grows increasingly stronger. But for this too happen it can’t be too cold or the water will freeze, which can crack or deteriorate the slab. Concrete blankets prevent this from happening.

If small cracks form in your concrete, fill them immediately with a concrete crack filler to prevent them from getting worse.

I’ve been a mason for over 25 years and have seen concrete slabs completely destroyed because they froze before curing strong enough to resist freezing on their own. When pouring concrete in cold weather, curing blankets are essential.

Blankets are applied after the concrete is pumped in place, spread out, and worked with a concrete tamper, screeds, floats, shaping tools, sponges, and trowels. They’re the last step that protects your slab so it can cure properly in cold weather.

If you have any questions email or leave a comment below.