Scratches & unclean spots after pressure wash

jaffet jefferson
I cleaned a metal roof recently using standard pressure washing for a client. I have cleaned many roofs using clean water and pressure washer over the years with no problems. For this particular house, there are a few spots where the apparent algae/bacteria wont remove unless scrubbed aggressively. Additionally, the client is claiming that I caused scratches on the paint from the pressure washer. He now wants me to "repair" the roof. 1. Can a pressure washer cause scratches on a metal roof? 2. Why do some areas not come clean when washed?
Eric Novotny
An informed customer is the Best Customer!
If the paint finish is compromised, anything can cause it to chip off whether it be abrasion via the brush or even mild pressure. The paint is likely taking on the stains because it has begun to degrade and there is some surface porosity where there wasn't before. Sounds to me like the paint is on the way out and you may have been the unfortunate soul to last touch it which unintentionally makes it your project at that point in the customer's eyes. You might want to track down who the panel manufacturer is and see if they have a warranty on the panel and any approved cleaning techniques that you can document for your issue.
Todd Miller
Isaiah Industries, Inc.
Some qualities of paint systems are better at resisting staining than others. What I see in the photo are chips in the paint, not scratches. The fact that all of the chips are on or immediately adjacent to a bend in the metal indicates to me that the paint system was fractured during the original forming process and now, with age, the paint is not well adhered in those areas. Thus, the power washing is causing it to chip off.

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