When doing DIY concrete jobs at home or on the job the first question that usually comes to mind is how long does it take to dry? Concrete is everywhere. We use it to build structures like basements or garage floors, driveways, paths, patios, pillars, pavers, and more. So, how long does Concrete take to dry?
Concrete takes 12 to 48 hours to dry before you should walk or stand on it, 10 days before you should drive on it, and it takes 28 days to cure fully. Exact time to dry is dependent upon various factors, such as temperature, relative humidity, its ingredients, and level of hydration.
This article will explore the drying and cure times of various types of concrete, both regular and quick-dry, and how to mix your concrete.
How Long Does Pre-Mixed Concrete Take to Dry?
In the age of mass production, it is not necessary to make concrete from scratch since pre-mixed concrete comes in bags. The pre-mixed and pre-measured bags are not only straightforward to use but also convenient to store.
Before heading to the home improvement store, some basic knowledge of the differences between the various types of pre-mixed cement will save you time and aggravation. There are three basic types of concrete mixes: fast-setting, high-strength, and crack-resistant.
How Long Does Fast-Setting Concrete Take to Dry?
Fast-setting concrete is a blend of fast-setting cement, sand, and gravel, and generally sets in 20 to 40 minutes. It is best suited for posts or slabs, basically anything that needs a quick dry time. After 4 hours fast setting concrete will be cured enough to hold weight.
How Long Does High-Strength Concrete Take to Dry?
High-strength concrete is a mix of cement, sand, and gravel with additives. It sets in approximately 10 to 12 hours. It is best used for foundations, deck or step footers, or putting heavy equipment on. High strength concrete is strong enough to hold weight after 48 hours.
How Long Does Crack-Resistant Concrete Take to Dry?
Crack resistant concrete takes 5 days to cure in warmer weather(70F+) or 7 days to cure in colder weather(less than 70F). rack-resistant cement is a pre-blended mix, similar to high-strength, and best used for patios and walkways. Crack resistant concrete will be at full strength after 28 days.
Before tackling any project, you will need to know how many pounds per square inch (PSI) the concrete will hold once cured. For instance, you will use one PSI if you are building a bench and another if you are building a patio.
Lowe’s Home Centers carry Quikrete, so it is best to first visit Quikrete for specs related to their products (source). Home Depot carries Sakrete, and they also have a website where you will find the specs on their products (source).
Hydraulic Cement, Mortar, and Grout
When determining drying time, it is vital to understand the differences in various types of concrete. The general rule of 24 to 48 hours and 28 days to completely cure is a useful guide. However, there are differences in types of cement, which all contribute to drying or curing time.
Hydraulic cement is a type of cement that uses water, which produces a chemical reaction, to set and dry (source). The most commonly used hydraulic cement is Portland cement. Portland cement is not a brand but, rather, a type of cement comprised of 5 to 15 percent limestone (source).
Mortar is a mixture of fine aggregate material and cement paste. The primary purpose of mortar is to fill the in-between spaces in concrete, bricks, or even around pipes. Grout is a type of mortar or paste used when filling the crevices between floor tiles, around tubs, sinks, anywhere there is a small space to fill (source).
Drying or Curing Concrete
On average, you can walk on cement approximately 12 hours after pouring, and a post should be set in 20 to 30 minutes if you use quick-setting cement. However, quick-setting concrete needs more time to cure before it is dry enough to stand on.
If not properly cured, the cement will be weak and will not hold up to everyday stress or weather. If you apply too much weight on it before it cures, you could break your brand new concrete before you ever get to use it.
Curing the concrete that you have painstakingly poured, leveled, and smoothed is the most critical step in your project. Concrete takes up to 28 days to dry or cure full. For it to be strong and resist cracking, it must be kept hydrated during the curing process.
The first few days after you have poured the concrete are especially critical. Water needs to be on the surface of the cement. If water is not on top of the concrete, it will dry too quickly, which produces a weaker product. Before you make a swimming pool out of your concrete, lets go over exactly how to keep your concrete hydrated.
How to Hydrate Concrete During the Curing Process
The best way to keep your concrete hydrated is to spray water on it from your hose over the first seven days after the initial pour. Moist curing, or keeping the concrete wet, makes for a 50 percent stronger outcome. However, this only applies in hot weather, and you should not use this method during months where temperatures get below 60 degrees.
You also need to keep your concrete covered. You can find concrete curing blankets, or a polyethylene sheet 4mm or thicker will work just fine. Give the surface of the concrete a thorough dousing with the hose, cover it, and use heavy objects such as bricks to hold it down. Do not put the weights on the concrete. Repeat this process every day over the first seven.
When you are spraying your concrete with water, do not let it come straight out of the hose and onto the concrete. That will create a lot of divots all over your slab where ever the water hits. Instead, use a nozzle with a misting setting. By using a misting nozzle, the small drops of water will not cause any cosmetic damage.
The Pond-Curing Method
A method known as pond-curing is just as effective as moist curing and takes less time with some additional effort. Once you have poured the slab, build a temporary dirt berm around it. Then flood the area with one foot of water. The concrete slab will now cure in three days rather than seven.
The drawback to pond-curing is the immense amount of soil needed to build the berms. For the average homeowner, the pond-curing method is impractical and you are better off misting your concrete daily.
Curing compounds contain soluble emulsions, are readily available, and offer a much simpler solution to the other methods. You spray the emulsions onto the surface, and they form a protective film over it. Water is then unable to evaporate, and curing happens at a consistent rate.
Curing compounds do vary. Some will disintegrate in about 14 days, and others will need to be scrubbed off with a scrub brush once cured.
Another permanent option is the Quikrete Acrylic Concrete Cure, which penetrates the surface and virtually waterproofs the concrete. Its main advantage is a freshly-poured look every day.
Before purchasing a curing compound, thoroughly read the label. The closer the product meets your specific needs, the more exceptional your project will look.
Cement or Concrete?
While all concrete is cement, not all cement is concrete. In other words, cement is an ingredient in concrete.
Cement is unique but not strong enough on its own. It is a binding agent used to make all the ingredients in concrete stay together. Cement comes from clay or limestone, which are both rich in calcium and silica.
To be used as a binding agent, you must add water, and the cement is ready when it has the consistency of paste. The amount of water used will affect drying time and workability.
Concrete is an aggregate mixture of cement and rocks and sand. It is considered one of the strongest and most durable materials in the world. Concrete is plastic like, not rigid when poured, and can be shaped and molded before drying.
There are other ingredients used in concrete and, if mixing your own concrete, you need to choose them carefully. As aggregates comprise a large portion of the concrete volume, the type and size will make a tremendous difference.
Be certain your aggregates are clean and that your water is low in chemicals like sulfates and alkalis. These may affect the cement’s chemical properties and cause the concrete to be less stable and durable (source).
An excellent high-quality cement paste, such as Portland cement, is produced by lowering the cement’s water content without sacrificing its moldability. Using less water is not a problem as long as you pour the concrete correctly and do not take too long to consolidate or spread it. You don’t want it to cure or dry too quickly.
Drying and curing are very similar terms and, although similar, there is a difference. When your project is dry, you may walk on it or even put those gorgeous flowerpots down. However, the time the cement takes to cure is the time in which it will become substantially stable.
Fast-drying cement will be dry within 20 to 30 minutes and, depending on the type of cement mix you are using, the drying time increases. However, no matter how quickly the cement dries, it still takes up to 28 days to fully cure.
You have taken a lot of time to plan and execute your project. Do not get excited and put weight on the concrete before it’s ready. Wait for it to cure fully, and you will enjoy the fruits of your labor for years to come.