How do you remove black stains from concrete sidewalk? (2023)

Why is my concrete sidewalk turning black?

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.

Sponge the bleach solution onto the stained surfaces and work it in with a scrub brush. Keep the stained areas damp for five minutes, sponging on more of the bleach solution as needed to keep it from drying. Then rinse thoroughly with water.

If you have greenish-black stuff on your concrete patio, it's probably mold, mildew, or moss. Damp or moist conditions from rain or humidity can encourage mold and mildew to grow in those nooks and cracks of concrete pavers or bricks.

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.

In other words, Rolf, your friend is correct: chewing gum makes those black dots that mar white concrete. The culprits are those who litter sidewalks with their castaways. Other persistent stains are caused by coffee, cola and other acidic liquids, but the spots are made by squashed gum.

The best solution is to scrub and clean the affected areas with a mold-killing detergent, like RMR-86 Instant Mold & Mildew Stain Remover, or a simple solution of household bleach and water. Be sure to scrub aggressively to get down into the pores of the concrete.

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.

As the water evaporates to the surface and soaks into the cement that is an ingredient of concrete, it leaves behind darker spots where the cement contains more moisture. These will fade over time as the water eventually soaks into or evaporates out of the slab.

You can also use hydrogen peroxide-based cleaners instead of dish soap. Let it sit on the wet stain for about 10 minutes or so, then scrub in a circular motion until the stain is removed.

Etching – Vinegar's ability to dissolve CaCO3 will dull your marble, travertine, concrete and terrazzo surfaces. It may “clean” the surface but it is also dissolving pits into the finish and effectively dulling it.

What stains concrete permanently?

Acid staining is a chemical reaction that permanently changes the color of the concrete surface. If you want to stain old concrete, using a true acid stain is always the best option.

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.

Although concrete stain is permanent and won't flake off like paint, it penetrates only the top layer of the concrete surface and will eventually wear away as the surface is worn by traffic or weather exposure.

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.

You can fill a spray bottle with a 50/50 mixture of vinegar and water, adding a few drops of liquid dish soap. Spray this solution directly onto the concrete, letting it rest for around half an hour. If you leave it on too long, the vinegar can eat through concrete parts.

Rinse the bleach off with a hose. If those stubborn stains aren't coming off, mix oxygen bleach with water to make a paste that's the same consistency as peanut butter. Apply to stained areas and let it sit for an hour.

Homeowners often use baking soda and a stiff brush to remove their driveway stains; pour a generous amount of baking soda over the stain and scrub it well with the brush. Let it sit for at least 30 minutes so that the baking soda has time to remove stain particles, then rise off with a hose.

Concrete discoloration is not a rare event

The use of too much or not enough water. The use of calcium chloride. Improper concrete laying techniques. Outside temperatures.

You might think that pressure washing is the best way to remove algae. However, the force of the water can cause your shingles to lose their protective granules. Pressure washing can even tear shingles off your roof! Some homeowners also try to get rid of algae by using bleach.

Your black algae problem typically won't go away on its own. Not without fixing the cause first – and even then, established algae in your tank will probably require a little effort on your part to banish it for good.

Does vinegar damage concrete driveways?

Vinegar does not dissolve concrete itself but can degrade the cement that binds concrete together. As a weak, dilute acid, vinegar will cause only minor damage to concrete but can take the shine off polished surfaces. It can, however, be used to remove small amounts of cement from tools.

If you don't have tea tree oil or don't want to use it, this homemade concrete cleaner will still be effective due to the addition of baking soda and peroxide. They work together as an anti-fungal, but also whiten and remove the stains from mildew.

What chemical will clean concrete? If you have mildew stains, the best chemical to clean concrete is trisodium phosphate. Combine two tablespoons of the chemical with two tablespoons of powdered laundry detergent and one-quart water. Then, apply it to the stained area and scrub using a stiff brush.

Although it's possible to scatter the OxiClean powder on the wet concrete and then scrub with a stiff broom, you'll probably get a more uniform result by mixing the powder with water first. Use four scoops of powder per gallon of water. The powder mixes best into warm-to-hot water.

Factors influencing the discoloration are calcium chloride mixtures, cement alkalis, hard surfaces, inadequate or insufficient curing, wet subsurface, varying proportions of aqueous cement on the surface, and changes in the concrete mixture. Discoloration from these causes appears very soon after concreting.

Black mold growth on concrete takes on the appearance of black spots, larger circular formations, or complex solid growth over an entire wall. Black mold in small amounts could also be mistaken for common mildew around damp basement areas but is much more dangerous.

If you neglected cleaning your concrete patio for some time, use a detergent such as Dawn or Ajax dishwashing liquid mixed with water to help brighten the surface.

If you need to get rid of rust from concrete, your best bet is to use some WD-40 Multi-Use Product, and some elbow grease. WD-40 is specially formulated to be a penetrant, so when you spray it on a rusted surface, it gets to work right away by getting under the rust.

Clean Concrete Floors With Bleach

As a gentler cleaner, bleach can't harm concrete's durable material. Aside from being an effective cleaner and stain remover, it also acts as a disinfectant to the concrete surface.

These two common household materials can serve as natural cleaners to remove grime and keep your surfaces clean. Because vinegar and baking soda are on opposite ends of the pH scale, they can be combined and used as effective cleaning solutions.

What not to clean with vinegar?

Combine 1/4 cup of liquid bleach with 1 gallon of hot water in a large bucket. To avoid damaging your lawn or walkways, always dilute your bleach and control your runoff when rinsing. Soak your brush in the solution and scrub the entire area until it's fully saturated.

Vinegar is a natural and safe alternative to cleaning concrete with harsh chemicals. In the case of algae and mold, it does a better job than bleach, and it is better in the long term for killing these infestations. Oftentimes, vinegar can be found in your home or garage.

Concrete driveways are prone to dirt, residue, mold or mildew. Yes, you can clean them with bleach. In fact, bleach not only removes many stains, but it also deodorizes and kills mold and mildew when used properly.

For a natural solution for getting rid of black mold, combine one part baking soda with five parts distilled white vinegar and five parts water in a spray bottle. Alternatively, you can use a chemical-based mold and mildew remover, all-purpose cleaners, bleach or dish soap.

White vinegar is a mildly acidic product that cleans, deodorizes, and disinfects. It can also kill 82% of mold species, including black mold, on porous and non-porous surfaces. You can use it safely on most surfaces, and its offensive odor goes away quickly. Pour undiluted white vinegar into a spray bottle.

Vinegar truly is better than bleach at killing mold. The EPA does not recommend using bleach to kill or remove mold, except in special circumstances. In most cases, “a background level of mold spores will remain” after the application of bleach.

You can also use hydrogen peroxide-based cleaners instead of dish soap. Let it sit on the wet stain for about 10 minutes or so, then scrub in a circular motion until the stain is removed.

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.