Concrete Curing Blankets
Learn how a thick insulated blanket is essential to curing concrete in harsh winter climates. We’ll explain curing blankets, how to use them, why use them, how to “tuck” concrete in to cure, and best practices to cure crack-resistant concrete for stronger structures.
What Are Concrete Curing Blankets?
After concrete is mixed, it’s left to harden within a form structure. This process is called “curing,” and it usually takes up to 28 days. During curing, the concrete dries from the inside out, becoming harder, stronger, more durable, and crack resistant.
But if temperatures drop below 40° F, the water inside the concrete may freeze, and this can create a weaker concrete, causing structural damage down the road. Also, if there is snow or rain while the concrete is curing without a cover, the concrete may absorb the extra moisture, becoming less durable, and take even more time to cure.
For this reason, thick, rainproof, insulated curing blankets are used to hold in the heat; and some curing blankets are even electric for extremely harsh winter conditions.
How to Use Concrete Blankets
Using concrete blankets is very simple. Just lay them on top of the concrete. But there are a few things to consider when selecting the correct blanket:
- Get a current weather forecast for temperature and if rain or snow is predicted.
- Use a temperature gun to measure the ground temp. If the ground is extremely cold, you may want to warm the ground with electric curing blankets before pouring the concrete. Remove the blanket after warming the ground, but before the pour.
- Determine the sizes and number of blankets you’ll need. Be sure you have enough to cover the entire surface, overlapping all seams. Check with a White Cap sales associate or online for sizes and pricing. Be sure to include this cost in your project budget.
- Estimate how much insulation is needed. Usually a single blanket is enough, but for some jobs, heated electric blankets or multiple layers may be needed. Your experienced White Cap sales associate can help you.
- Plan on using extra blankets around the edges and corners. This is where most heat loss will occur. Either get thicker blankets or stack them.
When to Use a Blanket
Cold temperatures drastically impact concrete as it cures. Curing blankets aren’t used in warm regions. Northern regions and climates with mild winters that receive snow or freezing temperatures infrequently will need curing blankets. The same is true for states like Alaska where it’s almost always too cold for concrete work.Approximately 15% to 20% of mixed concrete is water. During curing, most of the water slowly evaporates as the concrete strengthens. But when that water freezes, it can expand up to 10% in volume, destroying internal bonds, causing the concrete to become flaky, and even turn into powder. The concrete’s structure, strength and durability is dramatically weakened or destroyed.
R-factor Insulation
Concrete blankets are insulated to keep heat in and cold air out. Blankets offer an R-factor which will vary from manufacturer to manufacturer. Some companies boast of 6-layer foam insulated blankets, but it’s pretty rare to require that many layers.If you need help in choosing the best curing blankets for your projects or want information about waterproofing and R-factor values, talk to an experienced concrete White Cap associate.
Waterproof
Most blankets have a waterproof polyethylene exterior shell covering. The interior is made from the same material so if water seeps through the exterior shell, it won’t reach the concrete.The Types of Concrete Blankets
Curing blankets come in two main types: Electrical and insulated.
Electric Blankets
Working similar to the electric blankets on your bed, electric concrete curing blankets use electric wire coils and loam insulation to trap heat in. Electric blankets can be used with or without electricity.
Insulated Blankets
Made with a heavy polyethylene outer shell that keeps the internal polypropylene foam insulator dry, both layers are water resistant, keeping rain, ice, and snow out while keeping the concrete interior just moist enough as it cures.
Wet Cure Blankets
This rarely-used blanket is not heavily insulated and not used in very cold areas. But it works great in dry zones. You can wet the concrete down if it’s drying too quickly, then cover with a wet cure blanket. Moisture will be locked in, preventing rapid drying.
The Benefits of Using Concrete Curing Blankets
The perfect concrete placement is around 70° F in low humidity. Concrete needs to be not too dry, not too cold, not too humid. When environmental conditions are not “just right” then adjustments must be made.
Here are some curing blanket benefits:
- Curing blankets allow concrete work to be done in cold climates as well as hotter zones.
- Blankets 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.
- They’re easy to fold up, transport and re-use.
- Blankets can speed up the rate at which concrete cures.
- They’re tough and durable.
- All blankets are easy to use. After finishing, just lay them on top of the concrete to be cured.
Once the curing blankets bring the concrete’s temperature up to 50˚ F you should keep them in place for at least a few days. You can check the concrete’s temperature with an infrared gun or use the Maturity Method. This is a non-invasive method to test the compressive strength of curing concrete in real-time. Using a chart, a "maturity index value” can be calculated by referencing the concrete's temperature, cure time and elevation.
Concrete Blankets Best Practices
- Make sure you have enough blankets to overlap seams.
- Create thicker layers on each corner, overlapping as necessary.
- Curing blankets come in a variety of sizes. Make sure you have enough to cover the entire surface to be cured.
- All the concrete surface should be covered. If there’s even a small area of exposed concrete heat will escape.
- With proper planning, concrete work can continue into late fall.
- The longer concrete can cure, the stronger it becomes.
- At 50° F, it takes nearly 6 days to cure the same concrete project that would cure in 3 days at 70° F. Once temperatures reach 32° F or below, curing time is significantly longer, and you run the risk of the concrete freezing.
Alternative Curing Methods
Some contractors are using chemical alternatives to curing membranes or blankets. These curing products are available in low or zero VOC solutions and can reduce or eliminate cracking due to curing, and often exceed requirements of water curing specifications. Ask your White Cap representative for more details.
Concrete Sealing in Cold Weather
A few degrees warmer or colder can be the difference between a long-lasting durable seal or a flaky, white powdery finish which may require replacing. And, that could mean the difference between profit and loss. Keep reading to understand how temperature and other factors can affect a sealer’s application.
Why Seal Concrete?
You can seal concrete within the first 2-28 days after pouring, or wait 6 months; it’s your choice. Whether it’s a concrete patio, hospital and school floors, or a commercial building, interior and exterior concrete needs to be sealed, and here’s why. - Sealers provide protection against water absorption and surface abrasions.
- Sealed concrete is more resistant to:
-
- Cracking, spalling, and pitting
- Freeze-thaw and salt damage
- Staining
- Mold and mildew
- Efflorescence
- Dusting
- Deterioration caused by surface abrasions
- Deterioration caused by water abrasions
Before applying a sealer, there are a couple issues that you should consider for an ideal application:
- Moisture
- Temperature
How Moisture and Temperature Affects the Application of a Sealer
After applying a sealer, there is a chemical reaction that happens during the drying and curing process that forms a hard, durable film that creates the seal. The temperature when you apply the sealer can either slow the process (too cold) or speed it up (too warm).All sealers have a minimum film-forming temperature, (MFT). If the temperature falls below or above the MFT, cross-linking won’t occur, and the sealer’s film will not join or harden properly. Signs of a failed MFT are white hazing, white dusting, and delaminating.
Ideally, sealers should be applied at temperatures between 50° F and 89° F for a proper film forming to occur.
Also during cold weather, other factors can influence how quickly or how slowly the sealer cures on top of the concrete. A local weather forecast should provide answers about:
- Time of day you plan to seal the concrete.
- Wind velocity during the time period for applying sealer.
- The amount of sunshine for the day and 48 hours after.
- Humidity levels for the day that the sealer will be applied. If high humidity is expected, you may consider rescheduling the application to a low humidity day.
- Dew point which influences humidity (higher dewpoint = higher humidity).
- Temperature – quickly obtained from a weather app.
- Concrete temperature may be obtained by using an infrared temperature gun.
The quality and the finished look of the sealer will be determined by these factors. This information will give you the option of rescheduling if necessary.
Every Sealer Has Unique Application Requirements
Be sure to read the manufacturer’s instructions on application because each product should specify the MFT for an optimal finish. If you have questions, ask a White Cap sales associate; they’re specially trained on sealer types, application techniques, and determining the best conditions for a successful application.Types of Sealers
The type of sealer you use depends on if the concrete is fully cured or if you want to seal concrete 2-28 days after placement while it cures.Silicate sealers are very popular because they increase the concrete’s strength while others chose a water-repellent sealer which protects again freeze-thaw damage and salt.
The type of sealer you use will depend upon how you want the finished product to look after being sealed and how often you want to reseal it.
- Silicate Concrete Sealer: Increases the strength and density of concrete, and reduces dusting, and deterioration caused by weak concrete and surface abrasions.
- Silicate Siloxane Water Repellent Sealer: Reduces absorption of water and other liquids on the surface and reduces deterioration and staining caused by water absorption. Sealed concrete is more resistant to freeze-thaw, salt damage, mold, mildew, and efflorescence.
- Siliconate Water Repellent Sealer: Reduces absorption of water and other liquids on the surface and reduces deterioration and staining caused by water absorption. Sealed concrete is more resistant to freeze-thaw, salt damage, mold, mildew, and efflorescence.
- Acrylic Concrete Sealer: Enhances and protects concrete with a wet look in low or high gloss finishes.
Solvents
Sealers are based on specific solvents. Avoid using a water-based sealer during cold temperatures because the sealer will dry slowly, and you’re taking a risk that the weather could change while the sealer is drying and curing. Also, water-based sealers may freeze when the temperature drops below freezing. Acetone is the fastest-drying solvent, and it’s best for cold climates.Spraying v. Rolling Applications
Spraying is recommended when applying sealers in cold weather because it leaves even, thin coats for the best cure.Some sealers are best applied by spraying because not every sealer is formulated for rolling. It depends on the solvents in the sealer. Slow-evaporating solvents are best for rolling.
If you spray on a sealer, back-roll on the primer’s first application. This will work the material into the surface, and it improves the adhesion. Some contractors sealing decorative surfaces, especially large areas, will use the spray/back-roll method.
Application Tips
- Whether spraying or rolling, apply sealer in thin layers.
- If you’re rolling on a sealer, dip your roller into the sealer often. Always lay the roller down next to the last area rolled to see where you stopped.
- Using a long nap roller helps cover more area and apply more volume for better coverage.
- Before applying a sealer, use a very light degreaser, followed by lots of water for interior concrete. For exterior surfaces, use a light acid solution with a thorough powerwashing.
- Be sure to let the cleaned concrete dry thoroughly before applying a sealer.
- Avoid applying sealer during the hottest part of the day. When the sun is overhead bearing down on the sealer, it will create an unattractive plastic sheen. Wait until late afternoon to apply sealer to exterior concrete.