Why Does Concrete Discolor? Causes and Prevention
Concrete can discolor for a variety of reasons, and identifying the cause of the discoloration can help determine the best way to fix it. There are also many ways to prevent concrete discoloration from occurring on the job site that start before the concrete even dries. Because concrete discoloration can take on many forms, learning how to identify concrete discoloration and its cause will help inform the next steps.
How to Identify Concrete Discoloration
Concrete discoloration can occur for several reasons, and appropriate steps are necessary to prevent or minimize the issue. Here are some common types of concrete discoloration and how to identify them:
If a white, powdery substance appears on the surface of concrete, this is known as efflorescence. This type of concrete discoloration can occur when salts migrate to the surface of the concrete. Efflorescence can change both the appearance and texture of the concrete.
Rust stains typically appear like brownish-red stains on the surface of the concrete. This type of concrete discoloration typically occurs because of iron or steel corrosion within the concrete. Steel reinforcements or metal objects on the concrete can lead to rust stains.
Oil & Grease Stains
If dark, discolored areas appear on the surface of concrete, this could be a result of oil and grease stains. This type of discoloration is typically caused by spills of oil or grease and can occur in areas where vehicles are parked.
If the surface of the concrete changes colors gradually, this is known as fading. This type of concrete discoloration can be identified by comparing the color of the concrete to its original color. An unaffected area of concrete may highlight the difference in concrete discoloration caused by fading.
When concrete is poured, it goes through what is known as a curing process, where the concrete mixture solidifies. If the concrete is not cured properly, this could result in concrete discoloration. Poor curing may lead to uneven color and texture of the concrete surface.
Causes of Concrete Discoloration
Identifying the cause of concrete discoloration is an important factor in determining the most appropriate methods for repair. Concrete discoloration can be caused by a variety of factors, including:
Inconsistent Concrete Materials and Mix
Inconsistency in the concrete materials and mix can result in concrete discoloration in multiple ways. If there are variations in the aggregate, then the type and size may affect the final color of the concrete. The color of concrete may also vary depending on the source and whether multiple types of cement are used in the same concrete mix. Inconsistent materials and concrete mix can also result in other issues with concrete, including cracking or poor strength.
Replacing Cement with Other Recycled Materials
Replacing cement with other recycled materials, such as fly ash or slag, can result in a variation in the color and texture of the concrete. Some recycled materials may have a different chemical composition, which can affect the final color and appearance.
Adding Extra Water to Concrete
Extra water in the concrete mixture can also cause concrete discoloration. If the concrete is colored using pigments, adding too much water can dilute the pigment concentration and result in a lighter or inconsistent color. Uneven hydration can also result in uneven coloration or a mottled appearance.
Inferior Concrete Build
Poor mixing, poor curing, and poor finishing can all lead to concrete discoloration. The concrete must be mixed properly before pouring and allowed proper curing time; otherwise, it can result in uneven coloration. Poor quality materials and poor installation could also result in concrete discoloration.
Placing Too Much Calcium Chloride on Concrete
Too much calcium chloride in concrete can also affect the coloring of concrete in several ways. Calcium chloride can react with pigments used for coloring concrete, which can result in fading or discoloration. Concrete may darken, especially in areas exposed to sunlight frequently, due to calcium chloride in the mixture.
Excessive Humidity and High Temperatures During Concrete Curing
Excessive humidity and high temperatures can affect the concrete curing process and potentially impact the results in a negative way. Excessive humidity may slow down the drying time of concrete during the curing process. High humidity can also result in increased water content in the air, adding extra moisture to the concrete mix.
Tips for Preventing Discolored Concrete
- Use high-quality materials throughout the entire process for concrete pouring, curing, and finishing
- Follow proper mixing procedures and manufacturer’s instructions on concrete mix
- Follow the proper curing process and keep the concrete moist
- Avoid excessive use of accelerators like calcium chloride and always use correct proportions
- Control the pouring and curing environment by protecting the area from direct sunlight or excessive humidity
Can You Remove Any Concrete Discoloration?
It is possible to remove concrete discoloration depending on the cause and severity of the issue. Concrete discoloration can be improved or removed in some cases using methods including pressure washing, surface grinding, acid washing, and sealing the surface. If the discoloration is too severe to be removed, staining or painting the concrete may be an option for creating a more even surface.
Forming America has all the tools you need to make your concrete pouring and curing a success. Learn more about our rental options or buy concrete forming products online and get started on your next project today.