The problem is that black moss or algae grows in the paver cracks. It can be removed by pressure washing, but it comes right back.
Use a Pressure Washer
If you have a small amount of mold or algae, you may find that the first two steps of drying out and sweeping the area is enough to remove it. If this is not the case, pressure washing is often quite effective in removing mold and algae from pavers, bricks or concrete.
The mold on pavers problem occurs when algae and/or mold and other fungal types grow on damp or moisture-laden pavers. The answer is to eliminate the presence of moisture from underneath. Without moisture, the algae/mold cannot survive. The key is a proper installation with the substrate being the most vital component.
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.
Green or black algae, mold and mildew, lichen, and moss can all grow on your outdoor concrete surfaces. These ugly growths spoil the appearance of your concrete, and some growths can even cause damage.
Black mold, a type of mold that can potentially pose health risks to humans. It produces mycotoxins, which are toxic substances that can be released into the air when the mold is disturbed or when it grows on damp or decaying materials.
White vinegar and baking soda solutions will need to be worked into the slabs in order to activate. Some patio cleaners will do most of the work for you, and you may find after leaving it to sit on your patio for 24 hours that most of the black spots have lifted.
Lichen black stains on brick
These damp conditions provide a fertile breeding ground for black spot growth stains – otherwise known as lichen. Lichen breed within the porous, uneven brick surface.
Black algae (Gloeocaspa Magma) appears on your driveway as dark grey or black streaks and smears. Black algae is a type of fungus that thrives in moist areas, in both the sun and shade. From a distance, it looks like ordinary garden dirt, but you can't wash it away with the hose.
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.
If your pavers have been sealed, which is a service that we offer, it's a lot easier to maintain and it does slow down mold growth for the simple fact that when your pavers are unsealed, that moisture will sit in the joints and make mold grow. Mold likes damp, dark areas.
The most common complaint we hear from our clients is “the weeds are growing in the cracks between the pavers and I'm sick of dealing with it!” Contrary to popular belief, they don't grow from under the pavers. Instead, airborne weed seeds blow around and drop to the paver surface.
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.
Scrub with Bleach and Water
Prepare a 50/50 solution of bleach and clean water to use with a soft nylon brush or pad. Allow the bleach and water solution to sit for about 15 minutes after the first scrubbing session, then finish the job by rinsing with clean water and using natural stone cleaner and sealant.
'Bleach will kill mold spores growing across a hard surface, but if the mold has extended below the surface, then white vinegar is the best choice,' she says. 'The vinegar will penetrate to kill the mold and mildew at the root, preventing it from regrowing.
Getting Rid of Mold and Black Stains
For this cleaning, you're going to simply need oxygen bleach and warm water. First, move away or cover any plants around the area where you're going to apply the solution. Bleach is a very nocive material for any biological life, that's precisely why it works so well against mold.
Chlorine bleach.
The chemical is harsh enough to kill the mould. It must, however, be diluted because it produces toxic fumes.
Mold is a type of fungus that develops in warm, moist conditions. It can look black, white, green, blue, brown, purple, or gray in color. Mildew—another type of fungus— often appears powdery and white, but it may look black, brown, yellow, or gray.
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.
Remember, if black spot stains are left for longer than 2-3 years, the algae roots can sometimes penetrate the pool interior and discolour your pool surface permanently.
Shock Your Pool
Shocking increases your pool's chlorine and other chemical levels and is a black algae killer. Now, because black algae are so difficult to kill, we recommend using four times the recommended dosage for your size pool.
In the same way that baking soda can be a spot treatment for black algae, household borax does the same for blue and green algae. Simply use the borax to scrub away algae that's sticking to your pool walls, then use the brush to dislodge it. Follow up by vacuuming up or scooping out the free-floating algae.
One of the best things for household stains is white vinegar, and the same can be said for how it targets stubborn garden dirt. This eco-friendly solution is made up of equal parts vinegar and water, which is then left to soak into the patio to correct any discolouration and also remove tough marks.
This is a common problem. It could either be mildew, or a reaction from tannin in the wood. Given that you have black residue on rocks, it may be mildew.