The dark gray discoloration is caused by varying degrees of hydration of the cement in the concrete, caused by the varying moisture contents in the localized areas of the total concrete.
Now, the reason the cement is gray has to do with the manufacture of Portland Cement. In cement manufacturing, Iron Ore is used as one of the main constituents, and Iron Ore is black in color, so when it is combined and melted with the other materials it tints the cement gray.
Concrete discoloration is simply the change of the designated color of concrete. This could be due to the presence of calcium chloride in concrete, cement and additives, improper curing, environmental conditions, and faulty finishing works.
In its natural state, concrete has a light gray color. However, over the last few decades it has become common to color concrete a variety of different hues. There are many techniques for coloring concrete that produce different strengths of color.
Cleansing — For mild discoloration, repeatedly flushing the hardened concrete surface with hot water, then scrubbing with a stiff brush, can reduce or remove discolored blotches. Acid treatment — If the discoloration is more severe, a mild acid solution of 1-3% muriatic acid to water can help remove the discoloration.
The dark gray discoloration is caused by varying degrees of hydration of the cement in the concrete, caused by the varying moisture contents in the localized areas of the total concrete.
Discoloration in later life can result from atmospheric or organic coloring; the concrete is just dirty. This type of discoloration is usually removed by high-pressure washing with high-pressure water and, if necessary, chemical cleaning agents. The use of calcium chloride on concrete can discolor the surface.
Bleach is commonly used to whiten concrete and is very effective at doing so if the initial stain is removed beforehand. Bleaching stained concrete white prepares it for any additional coloring treatments that you may wish to apply in the future.
Fresh concrete is always much darker than when it is fully cured and dry. Even uncolored concrete. Wait at least 7 to 10 days until the new concrete has hardened and dried. If the concrete is on a wet subgrade or there's underground water, it may stay dark for as long as it's wet.
Concrete discoloration is not a rare event
Laying concrete isn't an exact science, and there are a variety of factors that can contribute to concrete discoloration from the very beginning. These factors include: Variability in concrete mixtures. The use of too much or not enough water.
If water is used to cure, a lighter color is likely. Be certain to use curing, sealing, and cure-and-seal products approved for use with colored concrete and follow manufacturer's recommendations for application. Concrete will continue to lighten until it is fully cured.
It involves wetting the concrete slab often with water (5-7 times per day) for the first 7 days. This method ensures your concrete slab will be extremely strong and durable, because it allows the moisture to evaporate slowly, preventing cracks and shrinks.
Mold, black algae, green algae, and lichen can grow on your outdoor hard surfaces and make them appear dirty. Not only does it look messy, but it can be slippery and bring harm to your friends and family. Additionally, some strains can cause damage and be difficult to remove.
While the slab will harden and lighten in color before 28 days, don't be fooled into thinking it's done hydrating. If you plan to stain or paint the concrete, doing so before the process is complete can result in changes in the stain color or the paint peeling off.
Use a garden hose or pressure washer, and saturate the concrete surface with lots of water. Then let Mother Nature take effect. Multiple water-soaking cycles may be needed, and there is no guarantee that the color will lighten to the desired shade, if at all.
Gray cement(+) gets its color from raw ingredients that contain iron, manganese, chromium and magnesium oxides. To produce white cement(+), manufacturers must use limestone or other raw ingredients that include very low levels of mentioned oxides.
Most of the concrete hydration process happens in the first few days, but concrete is not fully dry until it reaches 28 days. It can be easy to be fooled into thinking the concrete has fully cured before 28 days because it will lighten and harden earlier. Be sure to wait the full 28 days to stain or paint concrete.
As moisture rises to the surface of the concrete, it carries with it the calcium salts from within the concrete. These react with CO2 at the surface, forming that white powdery dust. It can be worsened by exposure to moisture, such as rain. With no moisture movement, there is no efflorescence.
HOW DOES RAIN AFFECT CONCRETE? Rain falling on top of freshly laid concrete can damage the surface and compromise a level and floated finish.
Vinegar Solution
Vinegar is a multipurpose kitchen product that is excellent for removing cement stains. Vinegar should first be diluted with water in an equal ratio. Apply the solution to the trouble spots, then give it some time to absorb.
Simply adding black pigment to white cement creates lovely shades of gray that are cool in tone (bluish), but natural Portland cement gray is a warm, complex gray that has greenish brown undertones, and those undertones make it difficult to reproduce.
Concrete containing a blended cement of Portland cement and ground granulated blastfurnace slag (ggbs) will sometimes exhibit a blue tinge on the surface, after the form-face has been struck, during the first few days of exposure to air.
Since a non-reactive stain colors the concrete by filling the concrete's pores or by creating a film that sits on the concrete's surface, typical moisture-related problems include flaking, peeling, bubbling, blistering and dark spots. All of these can cause concrete discolorations.