Honestly, there are a lot of youtube videos out there claiming guys can make upwards of $50,000 per month after getting some gear at Home Depot or Lowes. Wrong. First, profiting that kind of money will take up to 6 full size rigs. If you run a rig full-time 4 nights a week (one 24 hr period for tune up and maintenance), you will need 5 rigs running with full schedules, and a 6th to rotate on expedited response. “But I only want to run just 1 rig for me and my family?” Well, youre going to have to generate $6,000 per month in work and it will cost you no less than $2,000 to operate it-and thats if youre an un-insured freelancer. Then there’s saving your profits for those big jobs that get called in, or when you need to rebuild a pump head….. Ok, enough about money. We will save that for another blog. We have to get the job done first before we get paid. So what about the equipment? We see the same scenario several times a year where people believe they can buy some equipment and spray off a sidewalk and call it good. Pressure washing is way beyond that. Pressure washing is the science behind identifying your substrate (surface), and the contaminant (dirt), and how it is bonded to your substrate. Next you have to select the method in which you will remove the contamination. Bear in mind, you may have an overly complex scenario (like a diesel engine or pool) or perhaps a very large one (like a parking garage). Either way you need to work quickly, and get the job done without damaging whatever it is you are working on. Fundamentally, pressure washing involves injecting water in between your contaminant and substrate. The only rule to remember here is that water is a non-compressible liquid. This means that no matter how hard you squeeze it, or how fast you move it, it will not change its volume. Next you have to consider the hardness of your substrate. Concrete? We’ve cut concrete with as little as 2000psi, but other industrial foundations can withstand 4000psi. Some metals will start to cut at 4500psi (without abrasive media). Paint can peel in as little as 1000psi (depending on the type). Also be aware of the custom facades soffits and fascias made of high-density styrofoam or even drywall -you can punch a hole in one with as little as 500. This is where knowledge comes in. How do I peel graffiti off of a brick wall? That brick might be able to take 2500psi, and the paint peels at 1000psi so we are somewhere between 1000-2000 with a 500psi error…(and stop saying “p-s-i”. Just say “pounds” or “bar” wherever you are from.) But there is a colored shadow of the graffiti left behind… Ok so now we have to consider what is happening at a micro level. Small particles of the paint were remain because paint is essentially a liquefied plastic. While it had an extremely low viscosity, it “glued” itself into the microscopic cracks and pits of the substrate (mechanical adhesion). The only way to get it to become soft again is by heat… LOTS of heat. Metals will absorb and conduct heat away from where you want it. Most mason surfaces reflect heat. Glass…lets just not put any heat on that right now, or ever okay? Lets talk about general temperature right now. What temperature does your contaminant “melt” at? Most interior paints will soften at 200*F while some exterior paints can take up to 275*F. Automotive touch-up aerosol cans will withstand 325*F. You cook chicken (or your face) at 375*F, so be careful. What you will be doing at this stage is heating water under pressure to prevent it from boiling off. This is what we call superheating. In scientific terms, you will be approaching what is called a critical point. Its the point at where there is so much pressure, that the vaporized (boiled) water will behave like a liquid and vis versa. When this superheated water exits the nozzle, it is still traveling so fast that it maintains an effective compression. Specifically, its traveling anywhere between 200-600 mph! (up to 8000 psi). This superheated water (is now semi compressible at this point) is injected into the substrate, and heat is transferred (softening your contaminant). As you move the nozzle away, the pressure is able to relieve itself, expanding violently, removing the soft contaminant with it. This is where you must decide what angle you shoot in, and be careful of that BMW parked next to your work zone. I know its dirty already, but the guy that drives that wrecked prius will try to gouge you for a $180 car wash. But now we have to consider what is called thermal expansion. Remember how we said not to put heat on glass? Well, the same can apply to really old or weathered concrete. Stress cracks can get bigger, and that creates problems on the foundations of walls etc. Rubber weather seals will melt and shrink. Worse yet, some oil based substances can gas-off and create flammable vapor clouds, even if they are mixed with boiling water (DONT ask how we know that). But in other circumstances, thermal expansion can work to your advantage, like chipping mineral buildups off of metal and mason surfaces (so long as you keep the substrate cool). In other cases, too much heat can warp or damage plastic drain pipes. So make sure youre not dumping too much heat into what youre working on, and make sure your runoff has adequate time/space to cool. Ok so what about the weird dark stain left behind? Typically that is some sort of non-miscible liquid that has soaked into your substrate over time (if youve ever tried to remove a piece of bubble gum that has sat for many years…or an oil stain in a parking stall…). So lets talk chemistry. You’ll need to know some fundamentals of chemistry. Acids, alkalis (bases), oxidizers, and organic (petroleum) chemistry. Alkalis are what we make soaps and detergents out of. They can dissolve most organics by allowing them to bond with water. Acids will neutralize Alkalis by turning them into salts (typically) and vis versa. Acids are great for oxidizing stuff and making it look frosty and white, but too much and you will burn most substrates. Finally, most synthetic items (paints glue etc) are made organically (petroleum products) and solvents must be used, so be careful about vapor clouds and confined space. No matter what, be sure to neutralize everything afterward using its chemical opposite, otherwise long term corrosion and damage can occur. Also bear in mind that a lot of acids and alkalis are known to be electrolytes-meaning they conduct electricity. This can cause shorted circuits and transformers, or you. Now that you have the basics of pressure washing, you need to have a strong understanding of what youre working on. If your doing mechanized equipment, being a diesel mechanic or hydraulic tech will be the experience that allows you to drive your work back to its job site immediately afterward. Same goes for electrical installations, and construction of buildings. If you don’t, accidental mistakes can get brutally expensive, or potentially hurt someone else. So next time you see that 12″ surface cleaner at your local hardware store, remember that is only one assembly of a few tools that make up the whole of pressure washing. Know what youre working on, its physical properties, the chemistry involved. Then you pick engine speed, volumetric flow, pressure (precharge AND operating), temperature (AND dissipation), detergent. Your motor, pump, pulley, unloader, heater, trigger, barrel, and nozzle are all different tools working in tandem on your rig, and should be configured to each job. Next, you should look for the safety hazards, and choose your technique. What about technique? Thats a whole separate ball game. Stay tuned.