Here's a list of things needed to perform this task in a professional manner.
I suggest using a commercial pressure washer that provides an average output of 4-6 gallons of water per minute, anything less than 4 gallons per minute will not operate a surface cleaning unit like the one pictured below in the next text module. The washer should also create 3000-4000 psi for this type of task, anything less will lower the cleaning efficiency and anything higher may damage or etch the surface.
You will also want to have at least 100 feet of matching high pressure hose and 50-100 feet of 3/4 inch garden hose to feed your machine.
Since we need a way to dispense a form of detergent onto the structure being cleaned, we will need to make use of a down-stream chemical injector that's attached to the high pressure outlet of the pump. If your machine didn't come with one, you will need to purchase one that matches your units output range. It should be an adjustable one or fixed at 20-25%. The injector will have a siphoning tube that gets attached to it for drawing out detergents.
We will be using 10-12% Sodium Hypo-Chloride (chlorine) as our detergent for this task. Please Note: using store bought bleach through a 20% chemical injector is not going to cut it! Actual Chlorine must be used for this type of application.
For a driveway having a 4 car capacity, you will most likely need about 3 gallons of Chlorine.
Make sure you have purchased at least a 20 inch wide surface cleaning unit before attempting to clean any flat-work.
And of course you will also be using your wand and tips that came with your unit. The tips most likely needed for this job would be your "white 40 degree" tip and your "black soap" tip.
OK that should be all we need to start cleaning a typical concrete driveway, sidewalk, patio or pool deck.
In the next section I will discuss how you should set everything up.
Setting Up Your Equipment
Setting up for doing flatwork is much easier than setting up for cleaning a house. When I say this I mean that there's not much prep or preference as far as a location for placing the pressure washer.
Before hooking up the 3/4 inch garden hose to our machine we should always purge that hose in order clear anything that may have got up into the male end of the hose while it was not in use. If it was outside and left open, things like lizards and small frogs may be inside it and we just can't have that going into the pump during operation. There should be a catch screen on the inlet of the pump but we will still damage the pump if that opening becomes blocked and an insufficient amount of water is flowing. So it is imperative to purge the line first. Run that hose for about 25 seconds then connect it to the inlet of the pump.
Next we hook up our 100 foot length of high pressure hose through the use of the quick connectors on the pump and hose end. Once this is done we again run the water so that it now flows through the pump and out of the high pressure hose. Run the water for 20 seconds then connect your wand to the other end of the high pressure hose.
Now since we are going to apply chlorine to the driveway or any other concrete surface, we will need to connect our "black soap tip" to the wand and have our container of chlorine ready to draw from. The container should be on the ground and about 1 foot away from the machine so that the injector feed hose reaches the bottom of the container at all times.
At this point we should be set-up and ready to go.
**Make sure that the water is turned on all the way before starting the machine**
In the next module below we'll talk about the techniques used for this task.
Assuming that the concrete surface has dark mildew on it we will first be applying the chlorine solution to it using a back and forth motion with your wand to evenly cover the surface. You will actually want to start at the bottom if you're doing a driveway with a somewhat steep slope to it. I also personally like going over the surface twice with the chlorine just so I know I got it good.
When you have totally completed this part of the task, be sure to rinse the chemical injector with clean water before storing the unit away until next time. The way this is done is the same way you pulled detergent through it. Set up a 5 gallon bucket in place of the detergent container and let the machine draw the water through the whole system until the bucket is empty. Use a minimum of 3 gallons of clean water and remember that the soap tip must be used to accomplish this.
Once this is done you can shut the machine down unless you have an inline ball valve connected between your wand and high pressure hose (chances are, you do not have one).
At this time, go ahead and change from the black tip to the white one on your wand so it's ready for rinsing later on.
OK now it's time to replace your wand with your surface cleaning attachment.
Once it's connected you will start the machine back up and go down to the bottom of the driveway with the cleaning unit. The reason for this is that when driveways are pitched all the water usually ends up down at the bottom and once it's down there it makes it more difficult to clean. That's why we clean down there first.
You will want to slowly take the unit from one side to the other until you've cleared an area wide enough for you to now start going from a bottom to top direction. You will know how fast you should move based on how clean the surface is looking. Try to leave the least amount of overlap as possible or you may end up with what we call "white lines" on the cleaned surface.
Once moving in the bottom to top direction on the driveway, you will want to only move the unit forward and back about 5 feet at a time and then start clearing another path right next to it. Repeat this pattern until you've reached the other edge of the surface. At that time you will be moving up to the next dirty area and doing the same thing all the way across. Keep doing this until the surface is completely finished with the surface cleaning unit.
Next we will again switch back to the wand already having the 40 degree tip on it and start rinsing the surface from the top to the bottom where all the water, agitated dirt and mildew will end up.
While rinsing, keep your tip about 8 to 10 inches away so we don't etch the concrete (we don't want to strip the lime from it and ruin the surface).
Once you're finished rinsing it off, you should be looking at a fairly clean surface unless the surface is really worn or had dark hard-water stains or oil on it.
Notice by using the surface cleaning unit you have eliminated hours of back breaking hard work, plus no more "zebra striping" left behind from those days when you used to actually use the wand to do all the surface cleaning.
Of course calling out a professional to do it, is even better yet :)
Now you know why we get paid what we get paid to be in this business.
Knowledge, Professional Equipment equals Professional Results.
Be sure to check out my other lenses on Pressure Cleaning.
If you have any questions concerning the process, please drop me a line, I'll be glad to help.