Mold and mildew thrive on moist, shady surfaces. It's actually a fungal growth that can be identified by black, brown, grey, or white spots or streaks that appear on your sidewalk, or other outdoor surfaces. Also, if left untreated, these growths can cause pitting and deterioration on some outdoor surfaces.
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.
Hose the moldy areas of the sidewalk down with a hose to thoroughly moisten them. The moisture will prevent the black mold spores from becoming airborne and spreading.
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.
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.
When rebar rusts, it can expand up to four times its normal size, which causes the concrete to crack and break apart. This type of rot can also be identified by red rust streaks running down a wall where water has seeped out.
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.
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.
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.
For each gallon of water, mix a cup of bleach. Use a scrub brush to scrub the mixture into any algae stains. Wait for 10 to 15 minutes before continuing. Rinse the concrete clean with a hose.
Lichen are white, brown, yellow and black (i.e. "black spot") biological growths that live on slate and concrete tiled roofs, as well as on concrete paths, monoblock drives, brickwork, and occasionally on wall render. Lichen can be very tough to remove and pressure washing alone is ineffective.
Whether your patio is sealed concrete or cement, or even sealed concrete pavers, a bleach and water solution makes it easy to clean away built up soil, stains from leaves and pollen, mold, mildew and algae.
Dish soap and water: Dish soap is a degreaser, and it works well to clean oily and grimy concrete. Create a cleaning solution of warm water and few drops of dish soap and apply it to the surface. Let it sit for a while, then mop the patio and rinse it with fresh water. Repeat the process as many times as needed.
The texture of the surface provides plenty of pores for dirt, moss, and other materials to accumulate. To remove stains and get your sidewalk clean, you'll need something that will also sink in and lift the offending soil.
Black mold, as the name implies, is often dark in color. When searching for black mold, look for circular-shaped spots that are black, dark green or dark brown. Some black mold can also take on shades of orange or have flecks of white within it. Most of the time, black mold has a slightly furry appearance.
While mold only feeds on organic materials, it can grow on any surface, especially concrete. While concrete may not supply an abundance of organic material, it provides just enough mold to spread to other areas of a building.
Pay attention to the color and consistency: We already talked about black mold above, though it's more accurate to say that Stachybotrys chartarum has a greenish-black hue. Toxic mold can also have a grayish, soot-like texture, or a slimy, wet surface. In some cases, you may even notice furry orange or brown spots.
It grows on cotton, wood, and paper products. It sometimes produces toxic chemicals that are found in its airborne spores and fungus fragments. These are called mycotoxins and are dangerous if they're eaten. There's no link to inhaled Stachybotrys chartarum mycotoxins and deadly diseases.
Our top pick is the RMR-86 Instant Mold and Mildew Stain Remover for its versatility and effectiveness on nearly every surface. For those looking for an eco-friendly mold remover with natural ingredients, we recommend CLR Mold and Mildew Clear.
Our top choice for mold and mildew, RMR-86 Instant Mold and Mildew Stain Remover, comes in an easy-to-use spray formula and kills all of these culprits on contact. Other types of stains are caused by manmade products, such as motor oil, paints, cleaners, and solvents.
Contact with wet cement results in cement poisoning. This can result in dermatitis, skin discoloration of dark blue or red followed by fluid-filled blisters that can lead to open sores and even amputation. Prevention is key to avoiding cement burns through the use of personal protective equipment (PPE).
Discoloration of a concrete slab is another possible sign of water damage in an affected area. The presence of water will make one area of the concrete darker than another.
Humidity based mold growth
Concrete is a poor insulator. During the winter months when the temperature drops, the cool surface of a concrete wall can cause condensation. In time this elevated surface moisture creates an environment conducive to mold growth.