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 on the surface of new concrete can be from several factors including inconsistent mixtures, too much or not enough water, low quality materials, poor workmanship, the use of calcium chloride, environmental issues, or issues created during the pore or during the curing process.
How long does it take concrete to turn from GREY to white? In warm, sunny weather, concrete should be nearly its final color after about two weeks. In cooler, damp or overcast weather, the concrete will take at least a month or longer to reach its final color.
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.
Although the bulk of the hydration process takes place in the hours and days immediately after the pour, concrete needs 28 days to fully dry. While the slab will harden and lighten in color before 28 days, don't be fooled into thinking it's done hydrating.
Going from a light to a dark color can be achieved with tinted sealers and colored coatings. But to go from dark to light, without making the surface look like it has been painted, often requires application of a micro-thin colored overlay.
There are two ways you can take a dark stain and make the final shade lighter. First option would be to dilute the acid stain itself. Second option would be to wash the stain off earlier in the process. In addition a second test patch should be done before completing the project.
The higher the water content of the mix, the lighter the color. Control of the water/cement ratio is vital for consistent color from batch to batch. These are factors beyond the pigment that can play a role in the final appearance of the product.
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.
Can I use a gray concrete and still get a white countertop? No. A true white color can only be achieved using a white cement mix. Add white concrete pigment to a gray concrete mix to create a sleek “ash” look that's popular in modern homes.
Iron oxide, which is present in some of the raw materials used in the manufacture of cement, is responsible for the grey color of OPC.
It contains a high amount of iron oxide and manganese oxide, which end up giving the cement that classic grey colour. It contains iron and manganese, but not in oxide forms, which end up giving the cement its white colour.
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.
Simply fill a spray bottle with equal parts water and vinegar (or water and baking soda), and add a little bit of liquid dish detergent. Spray the mixture on your concrete surface and let it sit for about 30 minutes. Then scrub and rinse your concrete.
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. Case in point would be random plastic or lumber placed on a concrete slab 24 hours after installation.
The biggest reasons why concrete changes color are calcium chloride, water, installation methods and the overall mix of your concrete. A low water to cement ratio affects the hydration of the cement which creates a darker color.
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.
White vinegar and a little scrubbing with a brush is a very effective, eco-friendly way to remove rust stains from concrete—even those that are decades old. Pour the white vinegar directly onto the stain, allow the liquid to penetrate the area for 20 minutes, and scrub with a stiff-bristled brush.
Pressure washing is one of the fastest, most effective ways to get your concrete white again. Concrete can change color over time due to pollen, algae, or dirt buildup, but a good pressure wash can easily remove dirt and stains and make your concrete look new again.
In warm, sunny weather, concrete should be nearly its final color after about two weeks. In cooler, damp or overcast weather, the concrete will take at least a month or longer to reach its final color.
Sealers, particularly solvent-based sealers, will darken concrete. If unevenly applied, it will create light areas where there is less sealer, and darker areas where there's more. If applied by sprayer, it may appear like “stripes”. Uneven roller application may leave darkened roller marks.
When the concrete is polished, tiny layers of the top of the surface are removed. Often times, for reasons described above, the paste on the top of the concrete may be darker than the paste just millimeters below. This condition may be corrected many times by deeper grinding to achieve a uniform color.
Will Vinegar Damage Concrete? Cleaning concrete with vinegar will not damage it! However, saturating concrete for an extended period will damage the cement that binds concrete together. Over time, vinegar erodes the concrete itself, so be careful.
To start, you'll need to have the existing surface mechanically ground down, both to prime the concrete to accept a new stain and to remove as much of the offending color as possible.
White washing is simply mixing white paint and water to lighten wood. The more paint you add to your mixture, the less opaque the finished look will be. So, if you're looking to just lighten your wood without covering the wood grain, then use mostly water with a few drops of paint.