Curing and drying are often used interchangeably, but, in fact, they are different. Curing is the process of controlling the rate and extent of moisture loss from concrete during cement hydration to achieve the desired properties for its intended use. Hydration refers to the chemical reaction that occurs between cement and water that contribute to setting and hardening. This requires maintaining enough relative humidity (greater than 80%) and a temperature above 40 degrees Fahrenheit for a period ranging between seven and 14 days—depending on the mixture. Techniques to achieve these proper curing requirements range from spraying the concrete surface with water in warm conditions to using heating coils and insulating blankets in freezing conditions. After the appropriate curing period, the cement will be adequately hydrated, and the concrete will be ready for full use.
Normal concrete will set in 30 to 90 minutes, depending on the humidity and temperature. However, you should ensure the concrete is properly cured before moving anything large onto it or exposing the surface to heavy foot traffic. Curing can take between seven and 14 days.
The minimum curing recommendation is seven days, provided that the temperature is more than 40 degrees Fahrenheit. However, compressive strengths of concrete mixtures vary, and each requires a different curing period. So, a good rule of thumb is to wait between seven and 14 days before full use.
The strength of concrete is measured in pounds per square inch (PSI) and is a measurement of the concrete’s ability to carry loads or handle compression. The higher the number, the stronger the concrete. Below are the most common concrete ratings every homeowner should know for general residential uses.
- 2,500 PSI: Useful for driveways and walkways. However, some may choose a stronger concrete to avoid excessive cracking.
- 3,000 PSI: A good choice for most residential applications. This can be used for driveways, patios and sidewalks. Its durability helps defend against freeze-thaw cycles of harsh winters.
- 3,500 PSI: This is a good choice whenever heavy loads are expected to be moved or stored, such as RV pads.
- 4,000 PSI: Typically used in large warehouse and factories, for the homeowner, 4,000 PSI concrete can be a good option for backyard workshops or sheds, due to its surface durability.
There are only three things certain in life: death, taxes and cracks in concrete. There are four main reasons concrete cracks:
- Too much water in the mix: A common problem with concrete used in residential work is excess water added to the mix. This could be an attempt to make the mix easier to work with, or just in error. Either way, too much water can dramatically reduce the strength of concrete and lead to cracking.
- Concrete drying too fast: Hydration, the chemical reaction that allows concrete to properly cure and harden, requires water. When concrete dries too fast, the water evaporates rapidly. This means there isn’t enough water present for long enough to cause the chemical reaction needed for a strong finished product.
- Improper strength of concrete used: Strength of concrete is measured in pounds per square inch (PSI). Using concrete that’s not strong enough for your project will undoubtedly lead to excessive cracking. Read our answer to the question, “What strength of concrete is right for me?” for guidance on what PSI you should use for a given project. Otherwise, consult with your concrete supplier to ensure the concrete is strong enough for the intended application.
- No joints: Possibly the best way to reduce cracking in concrete is by properly utilizing joints. These are either expansion or control joints. Since concrete is bound to crack, control joints are “planned” cracks. Omitting control joints from a concrete surface will only encourage the concrete to crack more—and wherever it needs in order to expand or contract. And expansion joints act as a type of “shock absorber” next to an adjacent surface to allow for the concrete’s natural movement. For more about concrete joints, read our “Why Use Concrete Joints” blog entry.
Cracks in your concrete? Read our “How-To: Repair Cracks in Concrete in Three Easy Steps” blog for an easy way to repair them.
Concrete is a mixture of three ingredients: cement, water and aggregate. It’s a material that is plastic in one form, but incredibly strong once dried. And it’s one of the most widely used building materials. In fact, it’s the second most consumed substance in the world, behind water. About 10 billion tons of concrete are produced every year.
Concrete is a mixture of three ingredients: cement, water and aggregate. Cement is simply an ingredient in concrete. It’s the binding agent—the material that ties the three ingredients together to achieve the hard, finished product we all know.
Portland cement is the most common type of cement used in concrete mixtures. It is a fine powder made from limestone and clay that has been superheated, then pulverized.
There are hundreds of different types of concrete typically used for industrial applications: prestressed concrete, precast concrete, shotcrete, lightweight concrete, high-density concrete and so much more. But for the homeowner, there are four main types you should know about:
- Normal strength concrete: This is the typical concrete made from the mixture of cement, water and aggregate that is used in too many residential (and industrial) applications to list. The strength of normal concrete can vary from 2,500 PSI to 4,000 PSI, depending on the mixture and intended use.
- Plain concrete: Refers to normal strength concretes with no reinforcement added.
- Reinforced concrete: Refers to normal strength concretes to which reinforcement has been added to improve tensile strength. Reinforcement typically comes in the form of steel bars, rods or mesh.
- Decorative concrete: There are two types of decorative concrete: colored and stamped. Stains and dyes add color to change the appearance of both interior and exterior concrete surfaces. And they can be added either during pouring or even to existing concrete. There‘s a vast selection of hues to choose from to achieve the desired effect. And stamped concrete is an easier and less time-consuming method for creating beautiful, multi-dimensional walkways and patios that look similar to more expensive landscape materials such as stones or pavers.
The most user-friendly method of removing stains in concrete is to use a premixed concrete stain remover, available at Intermountain Concrete Specialties. The two most common stains in concrete are oil and paint. If you’re looking for a home remedy, there are a couple of options— depending on the stain itself. Removing each requires a slightly different approach.
- Oil: Oil stains won’t scrub away. You’ll need to “pull” the oil out of the concrete. To do so, mix trisodium phosphate (available at most home centers) with water and an absorbent material (we recommend kitty litter crushed into a fine powder) to make a smooth paste. Apply some to the stain and wait until the paste dries. Then, sweep it away. If you’re dealing with an older stain, one application likely won’t get rid of it all. Be patient and repeat as needed.
- Paint: You can remove paint from concrete in a similar fashion as removing it from wood. Add a paint stripper to an absorbent material (such as kitty litter crushed into a fine powder) to form a smooth paste. Note: Paint strippers can be hazardous. Use only in a well-ventilated area and wear a respirator equipped with a vapor cartridge. Apply a thin layer of the mixture on top of the stain and wait 10 to 20 minutes for the paint stripper to work. Then, scrape with a plastic scraper. Next, scrub the area with a nylon or light steel brush and a little bit of water to remove any softened paint particles. Finally, rinse the entire area with plenty of water. As with oil stains, paint can be stubborn. Practice patience and repeat as necessary.