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 will continue to lighten until it is fully cured. Allow the concrete to cure at least 30 days before inspecting it for color match or appearance.
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.
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.
Slump of the concrete
Slump is a measure of viscosity. The more water added to concrete, the lighter the color is likely to be. Concrete placed and finished at a lower slump (dryer) will usually turn out darker and a closer match to the color chart.
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.
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.
If the concrete can cure consistently, the end result is usually a quality concrete product with consistent color and finish. If a foreign object retards the movement of moisture out of the concrete or traps moisture at the surface, a curing differential occurs, resulting in a color shift in the concrete surface.
This problem is called curing differential, caused by different levels of moisture at the surface of concrete during the critical first few days to weeks after pouring concrete. So, uniform curing is key to producing a consistent color concrete surface.
Concrete that is not moist-cured at all dries too rapidly, and reaches less than half its potential design strength. It will also have a greater number of shrinkage cracks.
The color of the sand affects the color of the concrete. High-strength concrete with a low proportion of water-cement is darker than low-strength concrete with a high water-cement ratio. proper placement, finishing, and processing timely curing.
In many cases, this is because of efflorescence. Efflorescence is that white powdery substance on the surface of your concrete that can appear over time. It can occur on anything containing portland cement and is commonly seen on concrete floors.
If the desire is to lighten the color, the best results I have seen come from pulling some of the initial stain out of the concrete. By using the carrier on which the stain is based (water, acidic water, acetone, alcohol, etc.), you can usually pull some or all of the color back out.
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.
Usually this white or off-white discoloration to concrete and masonry forms when soluble salts and other water dispersible materials come to the surface through capillary voids as a result of temperature changes, moist migration, condensation, rain, dew, and/or too much water in the mix.
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.
What are the causes of concrete discoloration? Concrete discoloration is a change of designated color due to calcium chloride in concrete, cement and additives, improper curing, environmental conditions, and faulty finishing works. What are the drawbacks of a high concentration acid solution on concrete?
This image shows that when a surface is covered by water boundary, the light beams that face the surface, will absorb to it. So there would be less light beams in the area for arriving to our eyes. As a result, we see the material darker.
By seven days, your concrete should be cured to at least 70 percent of its full strength. You will probably be able to drive on it without damaging it, although you may want to hold off on rolling heavy equipment over it. In 28 days, you can treat your concrete as fully hardened.
Curing times for concrete
Technically, concrete never stops curing. In fact, concrete gets stronger and stronger as time goes on. But, as far as we're concerned, to reach a practical strength, most industrial concrete mixes have a 28 day curing period.
Dark, blotchy appearance — When properly laid, concrete should look all the same shade, rather than showing dark blotches here and there. Light discolorations — Discolored concrete can also be seen in occasional patches of lighter than normal concrete in the overall 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.
DO spray new concrete with water. One of the most common methods for curing concrete is to hose it down frequently with water—five to 10 times per day, or as often as you can—for the first seven days. Known as “moist curing,” this allows the moisture in the concrete to evaporate slowly.