How does concrete get so dirty?
Concrete has small holes, pockets, and cracks that can build up dirt in them. Dirt, along with water from condensation or rain, can lead to organic material, such as algae or mold starting to grow on the surface. This can lead to green, black, or brown stains on the concrete and it is easily removable with a pressure wash.
Concrete also will get stains from rust or oil. Rust stains typically come from vehicles or other metals that have been on the surface of the concrete while oil is nearly exclusively from vehicles. Rust typically leaves an orange stain on the surface and if the concrete is on a sloped driveway it will run down the driveway. Oil stains are less prone to running down a surface but they will appear as a black, brown, or gray spot that is somewhat transparent.
How do I clean my concrete?
Pressure washing along with various chemicals will be your best solution to cleaning concrete with the previously mentioned stains.
If your stain is coming from organic matter, such as algae, mold, or dirt, pressure washing with a surface cleaner and a 5%-12.5% solution of sodium hypochlorite will clean the surface efficiently and completely. The sodium hypochlorite will kill the organic material and remove all spores still on the surface to prevent growth in the coming year or two. The high-pressure water will remove the dirt which should make the surface less hospitable to future spores that land on the surface. When pressure washing the use of a surface cleaner is essential as it evens out the pressure so marks are not left on the concrete.
If rust is the problem, chemicals such as RustAid can be applied and pressure washed off to great effect. Just simply follow the manufacturer's instructions and wear a mask and gloves if necessary.
If oil is your issue, pressure washing and chemicals can help alleviate but not entirely prevent the issue. Oil does not mix with water so pressure washing is largely ineffective on its own. When combined with a chemical such as Purple Power, an industrial degreaser, the oil can combine with the degreaser and that mixture can be washed away with water and pressure. This will likely need to be done more than once but each wash has diminishing returns.
If oil is your main concern and reason for getting a pressure washing service done, I would not recommend going with EcoWash. A company with a hot water washing system will likely lead to better results for your exact needs.
What are the risks?
Concrete can only handle pressures of 2500 to 4000 psi, with our service being approximately 2500-3000 psi, generally in the acceptable range. To mitigate this issue, the use of a surface cleaner is used to lower the pressure being applied on the surface.
Concrete less than 2 years old cannot be washed according to our company standards as it isn't always fully cured. This 2-year mark is set higher than most manufacturers recommend out of an abundance of caution. If your concrete is not fully cured you can get permanent streaking in the concrete from washing.
Concrete that has been sealed will likely have some sealant removed if a high-pressure wash is used. If your concrete is sealed, please inform your sales representative so the appropriate accommodations can be made. Using a lower pressure and more chemical would be the appropriate solution in this case.