Flat work and concrete cleaning is popular among all washers. We are not responsible for results while following these instructions as variables can vary greatly but this is what we do.
With a leaf blower blow off all the concrete that is a bout to be cleaned. You want to remove loose debris, rocks, etc.
Pre-treat concrete with a roof mix (you can use VERY little surfactant since you are cleaning a horizontal surface. The chem is not going anywhere, and this makes rinsing WAY faster if there is less bubbles to rinse off) + Red Raider or degreaser of choice. Depending on size of job use a roof pump, or if it’s a small job just use a pump up sprayer.
Cleaning & Application
Clean the surface with a surface cleaner, start in the spot where you first applied chem, and end in the spot where you last applied chem this gives chem time to do its work.
Make sure you use a surface cleaner that is the appropriate size for your machine. Golden rule is 4” for every gallon per minute machine is rated at. EXAMPLE 4gpm machine = 16” surface cleaner max.
Rinse the cleaned surface off with your ball valve by twisting the ball valve about half way (this is equivalent to putting your thumb over a garden hose to create more pressure/rinse power) and take this time to try and clean up any edges/corners you could not reach with the surface cleaner.
Typically, if you get close enough with just your ball valve, the concrete will come clean.
Re-apply your pre treat mix (now called post treat, ha), and walk away! If you prefer, you can also use oxalic acid to brighten things. If there are rust marks on the concrete, oxalic is the only thing we have found that will remove the rust, and it does a GREAT job too. We find roof mix does a great job with pre-treat and makes things pop. We only use oxalic when there is rust that needs cleaning. Apply the oxalic, scrub, and the rust comes right up.
Oxalic acid comes in a powder, and typically directions come with it if you order from www.pressuretek.com. We believe the starting ratio is 8oz for every gallon. Be prepared to do a lot of stirring, it takes a while to dissolve, and the shelf life is VERY short. Once you mix it, you need to use it. You cannot store it and use it the next day.