Simply put, black stains on
Vinegar is a safe and effective mold removal solution, but if this method doesn't prove to be effective, then a heavier-duty weapon may be deployed: bleach. One cup of bleach mixed with a gallon of water should do the trick. Simply combine the bleach and water in a spray bottle and apply directly to the 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.
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.
Algae can create black stains as well. Algae needs moisture, and brick walls located underneath roof drainage or in shady, humid areas can quickly develop algal growth. Different types of algae can create different colored stains. Brick stains can result from black, green or red algae.
Instead of using the classic mold-killing treatment of chlorine, bleach, and water – which only kills the mold and doesn't also remove dead mold spores – you'll want to use undiluted vinegar.
Porous paving slabs allows rainwater to soak in the porous surface and are a hotbed for lichen stains and black spots to take hold on your patio. Fortunately this problem can be easily rectified with a good cleaning product. It does not need a professional cleaner to clean it off. You can DIY with Black Spot Remover.
Black stains on stone are quite often caused by a cyanobacteria (Gloeocapsa sp. that not only stain the stone black, but also increase water absorption by penetrating veins in the stone (or marble, for example) leading to honeycomb weathering damage to the stonework.
To clean paver slabs, you can use a detergent, such as Dawn, or a vinegar-water solution that is gentle enough to effectively clean without causing damage to your concrete pavers.
The acetic acid in vinegar is a little stronger than acid rain, so exposing your pavers to this substance can lead to bleaching, corrosion and the loss of protective sealant.
Try Concrete Stain
The simplest path to reviving tired pavers is to apply an acrylic-based semitransparent concrete stain, such as Behr Premium Semi-transparent Concrete Stain ($27/gal.; Home Depot) or Valspar Semi-transparent Concrete Stain ($28/gal.; Lowe's).
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.
Islamic tradition holds that the Black Stone fell from Jannah to show Adam and Eve where to build an altar, which became the first temple on Earth. Muslims believe that the stone was originally pure and dazzling white, but has since turned black because of the sins of the people who touch it.
Desert varnish is the thin red-to-black coating found on exposed rock surfaces in arid regions. Varnish is composed of clay minerals, oxides and hydroxides of manganese and/or iron, as well as other particles such as sand grains and trace elements. The most distinctive elements are manganese (Mn) and iron (Fe).
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 ...
There are many environmental factors that can change how paving stones look. The two most common that you'll encounter are sunlight and water. The sun can make stones look lighter and might bring out certain colors while water can darken stones.
You can't cover your patio with copper sheets, but you can spray on a liquid solution of copper that will soak into the surface of the 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.
Avoid Leaving Moisture
Mold requires water and moisture to fester and grow. So if you manage to rid the area of water, the mold won't be able to grow. Patio maintenance involves keeping the area dry and clean thoroughly.
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.
WD-40 may remove paint stuck to brick if applied directly and in large quantities, allowing it to sit on the surface for a few hours.
Cleaning bricks with vinegar is an effective and natural way to remove dirt and stains. However, it is essential to follow proper techniques to ensure the brick surface's safety and achieve the best possible results.
Bleach (For Mold, Mildew, and Moss): A bleach mixture is ideal for removing mold, mildew, and moss from exterior brick walls. Combine a tablespoon of bleach with a gallon of warm water in a bucket, then apply the bleach with a sponge to the brick. Use a scrub to tackle hard-to-reach areas or difficult stains.
Water and mild dish soap is a popular cleaning solution because it's easy to find at home and it won't damage brick, but it will tackle stains. The BIA recommends using hot water for surface cleaning with a detergent. White vinegar and water, another common household cleaner, can also be used on mildew.