If your concrete has ugly charcoal-gray or black streaks or splotches, black algae is probably the culprit. Black algae can grow on many outdoor surfaces such as concrete or roof shingles and will thrive as long as there is moisture and sunlight.
Vinegar or baking soda: These natural cleaners work well to clean cement patios with stubborn charcoal or rust spots. Mix equal parts vinegar and water, scrub the patio with the mixture, then give it a good rinse. If stains don't dissolve, try undiluted vinegar.
Blackening of the surface is common when the concrete is “burned by late and vigorous troweling”. The more the troweling effort, the more compacted and dense the concrete surface becomes. The result is a reduction in the moisture content (water cement ratio) at the surface.
Vinegar and Baking Soda
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.
You can't cover your patio with copper sheets, but you can spray on a liquid solution of copper that will soak into the top surface of the concrete pavers. This copper will stop the growth of the pesky green and black organisms in their tracks. The easiest way to apply the copper is to buy copper sulfate crystals.
Spraying a vinegar solution (1 cup of vinegar per gallon of water) onto the surface, saturating it fully, should kill most strains of mold. Vinegar spray can be followed by power washing or manual hand scrubbing to remove the dead mold.
Use a mixture of water and white vinegar to spray down the area and kill the algae. Rinse the surface alga off the concrete with a water hose. Next, pour white vinegar directly on the surface and scrub using a brush. Use a vigorous back and forth motion.
Yes, you can use vinegar to remove mold from concrete. This household product is better than bleach when removing mold. Bleach may only remove surface-level mold, causing the latter to return over time. Mold, however, will die once it encounters vinegar.
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 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.
While it is designed to last for years after the initial application, the concrete can be made white again with diligence and the proper materials. Bleach is commonly used to whiten concrete and is very effective at doing so if the initial stain is removed beforehand.
The acid that molds produce can degrade concrete, compromising its strength and integrity. While mold may not find enough nourishment in concrete alone, it can feed on moisture, algae, bacteria, salts, dust, pollen, dirt, dead skin, and other particles trapped within it.
The patio black spots that grow on your garden stonework are actually spots of black lichen. The spores from the black lichen start life as tiny dust-like spores growing on the underside of leaves on trees and plants. These spores are carried, by the wind and the rain, onto your stonework in their millions.
Use a mild grease-cutting detergent such as Dawn or Ajax dishwashing liquid mixed with water and a natural or synthetic bristle scrub brush to help brighten the patio surface.
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.
Cleaning concrete with muriatic acid can be a highly effective solution if used correctly, providing ultra-bright white concrete and removal of many types of stains. In one application, you can remove rust stains, oil stains, algae, and paint splatter with a quick chemical application followed by pressure washing.
Mix one cup of bleach to 1 gallon of water. It can then be sprayed onto the concrete and scrubbed. Most of the mold should be removed through this method. A less aggressive method is to mix 1 cup of vinegar with 2/3 cups of water in a spray bottle.
Experts say they can do the trick for the patio as well. 'You can remove black spots easily from patios in an eco-friendly, low-cost way, with white vinegar,' says Laura Harnett, Founder, Seep. 'It has antifungal and antibacterial properties and will also stop the mould or lichen growing back.
When everything's ready, sweep or vacuum the steps to remove loose dirt and debris. Then mix three-fourths to a cup of bleach with one gallon of water, and sponge it onto all the areas where you see the green stains. Keep sponging on more as needed so the concrete stays wet for five to 10 minutes.
The black algae will take advantage of the surplus of nutrients and utilize them to grow and spread throughout the tank. Black Beard Algae can be a result of poor water quality, poor maintenance, overdosing fertilizers, low levels or fluctuating levels of CO2, too much light, or a combination of all of these.
Many aquarists dislike Black algae because of its stubborn nature, which is extremely hard to get rid of. Your black algae problem typically won't go away on its own.
Even if the black spots disappear, there may be “roots” beneath the surface, which is why scrubbing alone won't take care of the problem. Use chlorine tablets. Break a tablet in half and rub it directly onto the surfaces affected by black algae. This will help kill the roots and prevent it form growing back.