Welcome to MossWash
Oil stains on driveways not only looks awful but they are extremely difficult to get rid of. There are three main options:
Most rust stains can be visibly reduced by combining ingredients such as Vinegar, Salt, Baking Soda, Lemon Juice & Detergent. After mixing & applying the poultice and allowing the active ingredients to take effect (15mins to 1 day; cover with plastic sheet to avoid area drying out) then scrub with a bristle brush prior to rinsing down the surface. There are also some highly effective 'off the shelf' treatments that chemically dissolve rust from the stone surface. CAUTION - Only a few rust removers are suitable for natural stone surfaces,...
Unsightly and dangerously slippery, algae also makes the whole place look dank and unwelcoming. Not really the sort of image householders want for their most important asset. Fortunately, algae does little in the way of short term damage and can easily be treated and washed off any hard surface.
Many people like the visual appearance of moss. However, left uncheck it spreads quickly and becomes a real problem. Under these circumstances, it can cause a lot of damage to patio jointing, tarmac/block paving driveways and paths. Applying moss killing solutions to the area some weeks prior to pressure washing, using a rotary cleaning attachment, is the optimum way to shift moss with minimal damage to surface integrity.
Chemically treat, burn with a flame gun, strim, salt/nuke them and they still come back. At best all one can do is manage the area effectively. This involves a number of processes that if applied regularly, will achieve the desired outcome. Root removal is the key but it is a long drawn out manual process. When the weed roots get in between patio joints and block paving they do serious damage and in a worst case scenario, the area will need to be dug up and re-laid.
Pressure washing alone has little effect on these living organisms and an inexperienced operator can easily do serious damage to the stone surface. Once the area has been cleaned, the use of a sodium hypochlorite & water solution, applied and left for a period of time, will eventually kill off all the organisms. The process normally needs a number of applications before the infested area becomes completely clear but it is well worth the effort to get rid of them.