Roof Washing


Can You Clean a Roof With A Surface Cleaner? 0

It's been a long, busy day. But before I can feel finished for the day, I just feel absolutely compelled to have a lengthy blog post about the topic of roof washing with a surface cleaner.

A picture was posted in a FB forum showing a contractor using a Mosmatic roof cleaner along with a $99 special. A few of the comments related to the $99 special and most viewers commented that the technique (using the roof cleaner) was wrong. I've provided a link to a video and yes....I know it isn't an shingle roof....the video is just to show the equipment.

I posted a response stating that it isn't necessarily incorrect to clean a roof with a roof cleaner. And thus the bloodbath began.... Now....if you haven't seen a roof cleaner, you can just picture a surface cleaner that is guided with a rope down the slope of the roof.  I can feel the comments rolling around in your head already. Hang on before you crucify me. Hopefully I might be able to address them.

When the power wash industry began years ago, the theory was to blast the heck out of surfaces with as much force as you could get. Over time, the industry grew and practices improved with less pressure and better chemicals and techniques. In recent years, the low-pressure technique began to gain tremendous popularity particularly in the roof washing market and most new folks have adopted this method using low pressure chlorine compatible pumping systems. We have one that we've nicknamed the Bleach Beast

Asphalt roof washing is subject to great debate. Bleach? No bleach? Pressure? No pressure? Rinse immediately? Let Mother Nature do the rinsing? And some folks will debate the need to wash at all. Will washing void the warranty? Will bleach void the warranty? Will washing affect the shingle life?  In the last several years, there has been a ton of discussion and it gets heated with various opinions. If you research within the Roofing Industry, even THOSE folks are divided. But I did see at least one thing that everyone agreed pressure washing.

Oh I'm not done yet.  The key to that phrase was the word "pressure".  Many new folks in the industry have yet to really understand their equipment. And that's ok. We all had to start somewhere. We commonly teach folks how to adjust pressure with nozzle size rather than adjusting the machine's pressure unloader. The unloader isn't meant to be adjusted. Rather it should be set and then left alone.....set it and forget it. Need to reduce your pressure at the nozzle? Open the nozzle hole (use a larger orifice size) which will increase your flow and lower the pressure. I can lower your pressure at the nozzle to the gentle pressure of your garden hose if you wanted or needed. So while you are using a "pressure washer" you are not applying "pressure" to the roof. Your pressure washer is just the vehicle to deliver the water. 

Now let's add in the roof cleaning equipment to this discussion. Use the term "surface cleaner" and most folks will immediately picture a surface cleaner using high pressure cleaning a hard surface like concrete.  When we size nozzles for surface cleaners, we typically take the GPM and divide that by the number of nozzles and that will give us the correct orifice size assuming the user is not needing or wanting to lower the pressure.  But if the user wants to drop the pressure substantially we can easily do just that with a larger orifice size. I will attach a link to our Nozzle Chart that we use day in and day out just for your reference because it is a good tool to have around. With larger nozzle orifice, we can make that same surface cleaner that you use to clean concrete, gentle-enough in pressure to be used on a roof because at this point, you are not using "pressure" are now really just using the flow.  And in many cases, flow is actually more important than PSI.

Finally, let's talk about the mechanics of the surface cleaner. Surface cleaners can spin under lower pressures if the flow is adequate. An argument was made that a surface cleaner can not work under low pressure and the statement just isn't based in fact or reality. Will the bar spin at break-neck speeds? Nope....but if the idea is low pressure and minimal you really want it to spin at break-neck speeds?

It's important to understand your equipment, it's functional capabilities and how to repair it to really be successful in this business.  North American Pressure Wash Outlet has taught the Power Washing 101 and 201 courses at the Power Washers of North America convention for the last 4 years and we were honored with the Joe Walters Award for our commitment to the pressure wash industry. Our goal will always be to provide you education, equipment and soaps/chems to make your job easier. To provide you with anything less is not in our Mission Statement. And as business owners, we are committed to providing you with exceptional service and advice.



  • Kimberlee Handl