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What is Concrete Discoloration?
Concrete discoloration is the change in the color of concrete. When concrete not mixed properly it shows diffrent color from its original color.
Concrete discoloration manifests itself as darkening, streaks, stains and color variations. Concrete surface discoloration has many causes and different solutions.
Surface discoloration of new concrete can be caused by uneven mixing, too much or too little water, poor material quality, poor finish, use of calcium chloride, environmental issues, problems in porosity or during the curing process. It could be due to several factors such as: Sometimes the cause is obvious, sometimes it’s just a guessing game. It is important to check with your concrete contractor or concrete manufacturer before attempting to remove surface darkening stains. The most common methods of removing dark stains involve repeated surface rinsing and scrubbing with warm water or acid washing of concrete surfaces. After the concrete has fully cured, if discoloration persists after trying these methods, it may be time to apply a concrete coating to hide the discoloration. If you just want to erase the discoloration rather than cover it up, consider regular cleaning or a concrete coating.
If the cleaning method doesn’t work for you and you want to cover up the discoloration, you’ll need to use a sealer. Penetrating sealers don’t change the appearance of concrete, but acid stains and acrylic sealers do. Acidic stains create a marble-like finish where the acrylic sealer darkens the surface and leaves a low to high gloss finish. When applying acrylic sealer, be sure to apply a solvent-based acrylic and apply the product to a test area first to ensure the desired and consistent finish. The acrylic finish completely hides any underlying discoloration.
Causes of Concrete Discoloration
2. Low Quality Materials
Maintaining consistency throughout the injection process, especially during mixed dosing, is critical to avoiding heterochromatic stains. Different batches of concrete delivered to the site result in inconsistent colors.
Furthermore, it is difficult to produce a consistent concrete mix as it is composed of different materials with inherent variability. The constituents of concrete mixtures are cement, cementitious additives, sand, water, admixtures and sometimes fibers. Achieving consistent interactions between these materials in different batches of concrete is difficult.
Therefore, to achieve the best possible consistency in concrete mixes from different batches, all concrete components must meet his ASTM standards.
2. Add Water on Site
Contractors can add water to concrete batches to improve workability and make finishing as easy as possible. Changing the mix on-site without proper mixing produces concrete with a mottled appearance. When installed side by side, the difference in concrete color is noticeable. For example, when water is added to the batch and concrete is poured next to previous uncured concrete.
3. Discoloration of Cement
Another cause of concrete discoloration is the discoloration of cement used in ready-mixed concrete plants. The color of individual cements depends on the firing or grinding conditions during cement manufacture. Mold against discoloration if one type of cement is replaced by another during ongoing paving, or if a conditioned mixture is placed adjacent to concrete made with cement from another source You can observe the effect of the color of cement that does not fit.
4. Use of Cement Substitutes
Using recycled products such as slag or fly ash as a partial replacement for cement can result in color variations based on the percentage of recycled material in the mix, the ratio of water to cementitious materials, and how the concrete hardens. There is a nature.
Slugs initially have a light green or bluish tinge and lighten over time, while fly ash produces a range of shades from buff to brown.
5. Addition of Calcium Chloride
Calcium chloride is commonly added to concrete mixes to speed up setting time. This substance is responsible for the dark appearance of concrete, especially when its dosage reaches 2% of the cement weight.
If the mixture is not well mixed after the addition of calcium chloride, the color problem will be exacerbated, resulting in a more irregular or mottled concrete color.
6. Placement of Objects During Curing Process
Any plastic, wood, or debris left on the colored concrete during the curing process will cause the surface to become patchy in color and lighter in color where the material was sitting. This problem is known as differential cure. This is caused by different moisture levels on the concrete surface during the critical first days and weeks after pouring. Uniform curing is therefore important to produce a consistent colored concrete surface.
Plastic sheets applied to concrete to improve hardening play an important role in discoloration of the concrete surface. Discoloration caused by creases or air pockets in plastic or brine covers leads to so-called leopard spots.
Prevention of Concrete Discoloration
- Do not use calcium chloride in concrete.
- Do not alter the concrete installation method, such as changing the concrete mix, formwork, finish or curing. Severe and permanent discoloration may occur.
- We use consistent concrete raw materials that are continuously supplied from batch to batch.
- Proper pouring, finishing and timely curing of concrete reduce discoloration.
- Low quality ingredients should not be used.