Black spots show up on patio slabs when mould and algae have taken root in the pores of the flags, so while it is possible to remove them, you're going to need the help of one of the best patio cleaners.
Wash patio slabs with white vinegar
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.
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.
Simply put, black stains on flagstones are caused by certain types of mold and mildew. These fungi find their way onto the stones either from their spores landing on the stones or from simply extending onto the stones from patches of mold or mildew right beside them—a pretty common occurrence for garden pavers.
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.
Sanding and chiselling will leave unsightly marks on your paving, bleaching can work well but you have to be careful not to kill your plants and dilute your bleach to the correct level, some people recommend using this method only in the winter months to avoid damage to plants but you still need to be really careful ...
A solution of one cup bleach to four litres of water should do the trick. However,some stones may be discoloured by this so it is best to do a test run first. Another option is to use an undiluted five per cent white vinegar solution. Simply apply to the pavers and scrub with a soft-bristled brush.
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.
On the other hand, baking soda is useful because it is slightly abrasive, which is excellent for the rough surfaces of paving slabs. When it is mixed with water, it can dissolve dirt and grease, and like vinegar, you'll only need a brush or broom when cleaning.
Remove those ugly green and black mold stains on your deck with Wet & Forget Xtreme Reach™ Hose End. Spray your wood or composite deck with Wet & Forget no-rinse cleaner. Allow the surface to dry (4-5 hours). Let Mother Nature do the rest of the work for you!
Patio Magic contains a fungicide that will kill off the following: Lichens (mostly black spots, sometimes white, on patios, concrete and blocks). Mould. Algae.
With bleach, you want it to be a 5:1 (water:bleach) mixture and only use it on natural paving slabs such as stone. It will damage porcelain and other man-made materials. Also, remember to wear protective clothing so the bleach doesn't damage your skin.
How to Get Rid of Lichen. Believe it or not, you can treat your patio with something available, cheap, and effective: bleach or the stronger compound, sodium hypochlorite.
Vinegar is acidic. It can kill the lichen, which makes it easier to scrape it off the surface. Remove organic matter from the roof such as twigs, leaves and other debris. It can become a substrate in the future!
A cheap and effective remedy to get rid of lichen is by using detergent and bleach. Simply mix 3/4th cups of bleach in one gallon of water. Spray this on all places where you see lichen grow. Keep this mixture for 15 minutes and then remove all the leaves and wash the roof with plain water.
You can use bleach and water. You'll want to use one part bleach, 10 parts water to create a good cleaning mixture. Or you can do like the professional painters do, and use TSP or trisodium phosphate for a great cleaning solution.
'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.
Similar to cleaning pavers with muriatic acid, avoid an intense concentration of bleach, as it can damage the pavers.
Lichens are extremely tough to get rid of, so you'll need some specialist cleaning supplies to do the job. Look for a patio cleaner that contains sodium hypochlorite, also known as dairy bleach.
Let the solution sit: Allow the bleach solution to sit on the patio for 10-15 minutes. This will give it time to break down any dirt and grime. Rinse the patio: Use the garden hose or pressure washer to rinse off the bleach solution, starting at the opposite end from where you applied it.
White vinegar is good for cleaning pavers, though it's also acidic enough to erode the stones' surface. Diluted vinegar can be used safely to clean paving stones, though it should be used sparingly and infrequently to protect your paving from damage.
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.