Often times, since my company does all types of masonry work not just limited to the chimney, we get calls regarding to how to best clean moss, dirt, etc. from a brick patio. Brick patios are generally made of either actual bricks or brick paver stones, and cleaning brick paver stones and the like is easiest when using a pressure washer. Pressure washing the patio will remove actively growing moss the best. If the moss seems dead or if it is during a cold season that you decide to do this work, pressure washing should work.
One thing to avoid when pressure washing is actually damaging the brick or brick paver stones. A clean brick patio is not worth a cracked and chipped brick patio. For brick veneer keep your pressure at below 400 PSI (pounds per sq. in.). For regular bricks 100 PSI should do the trick. Start off with less pressure and only use the pressure absolutely needed to remove the stains on your patio. A pressure washer will remove dirt as well. A nozzle that causes the spray to come out in too tight of a stream is particularly prone to damaging your patio. Power washing is also particularly effective on black mildew stains as well.
For a completely beautiful patio you may still have some stubborn stains that can’t seem to be removed by pressure washing alone. To decide exactly which chemical is right for you, you will want to contact the manufacturer of your brick. Some chemicals are particularly harmful on certain types of brick or brick stone pavers. The
ChimneyRx Safer Brick and Masonry Cleaner is one product which I recommend if the manufacturer of your patio material does not have any qualms regarding it. It is safer than muriatic acid but still fights tough stains. Dilute each gallon with water at a ratio of 1:4. Each gallon of diluted solution will cover 75-125 sq. ft. depending on how porous your brick is. Using this product, a stiff bristle brush, and some elbow grease will aid in stain removal. Always wear safety equipment including eye protection and rubber gloves.