We have done it and it was not profitable at all for us. As everybody and their momma with a trip to Home Depot, is a power washing guru.
First get a guy to sweep up any concentrated mounds of dirt, that collect in corners or behind parking curbs. We use a couple echo back pack gas blowers to walk the dirt and dust/trash from one side of the structure to the other into a corner and collect it.
Like Shane mentioned above, we use a Rubbermaid trash can with a dump valve on it to walk the solution around and spread it with a wide push broom.
Pretreat the heavier or most used parking spaces with a good degreaser before applying your main cleaning solution.
Use an autoscrubber if you have one to agitate and pick up most of the crap, followed by a turbo with a truckmount to really get it nice and clean.
Using the autoscrubber accomplishes two very important things for us, it provide some agitation with a brush and after the first pass we recover most of the muck and dump into a sanitary, therefore keeping it out of the waste tank.
If you skip the Autoscrubber step you will need to spend a lot of time cleaning all of the sediment out of your waste tank and from what I remember, it is not a very fun task cleaning a Judson waste tank.
The turbo rinse is where you will see the greatest cleaning difference and will make your results stand out in the event someone else ever undercuts you and the level of results are important to the decision maker.
We just do it for our pharmaceutical buildings that just want to use one company and so we do it to protect the other service contract we have in place.
