At Powder Coating Services, when we receive a customer complaint we take it very seriously. It doesn’t happen often, and when it does we respond quickly and investigate the issue. Such was the case recently when a customer brought our attention to flashings that had gone through our powder coating process, and some 15 months later were showing signs of serious corrosion. This was a huge issue for the building owner, and not something easily remedied. Naturally, our customer turned first to us for answers.
Our immediate response was to look internally. Did the powder coating processes follow our strict quality control standards as required by our Qnet certification? Were the flashings properly pre-treated, was the powder applied to specification and was heat curing carried out correctly? Reference to our job card and batch processes, including quality control sampling and oven test records showed everything was in order. We had powder coated thousands of such flashings using our chromate system, and this was the first complaint. So where did the issue lie?
These flashings were installed on an architecturally designed residential dwelling in a coastal location. Our first hint of the problem’s cause came when the owner, a retiree with time available and wanting to take great care of his new home, explained his maintenance regime. No chance of salt spray settling here – the house received a thorough wash twice weekly, with hose pressure directed up and under the flashings to clean out any cavities. First problem: water was going into places no rainfall would ever reach.
But the homeowner’s cleaning rigor could not be the whole story. The flashings protected cedar weatherboard cladding where it finished under the soffit. If stainless steel fastenings had been used as per manufacturer’s specifications, there should still have been resistance to galvanic corrosion* where moisture occurred between flashing and fastenings on the cedar claddings. So now it was time to hear from the builder, and to learn that his sub-contractor had not changed the nails in his gun when fixing the boards under which the flashing would sit. When hosed down, the cedar acted like blotting paper, retaining moisture in the cavity area. That moisture in the cedar cladding then worked on the metal fastenings, and through them attacked the aluminium flashings.
So this unfortunate problem of corrosion and breakdown of the powder coat surface started with the design, was facilitated by the house maintenance technique, and accentuated by use of hardware inappropriate for the job. There was no issue with the powder coating process itself, nor with the suitability of a powder coated surface in this situation. Now the builder and his customer have a headache as they consider how to fix the problem. Once the flashings went on, they were never designed to come off again without major works.
We take great pride in our quality standards and how they are controlled. We stand by our work, to the point of helping our customers work through any issues that arise. In doing so we have the support of our major suppliers, in this instance our local Dulux representative, who provided valuable input as we worked through the matter. Powder coating is totally suitable for outdoor metal component finishes, but as with any other coated surface, it requires appropriate care and protection.
Read here what Dulux has to say about powder coat care and maintenance.
* Galvanic and electrolytic corrosion - what's the difference?
There can be confusion between galvanic corrosion and electrolytic corrosion, with the latter often getting the blame for damage caused by the former. The distinction is quite simple: galvanic corrosion is the interaction between two different metals, whereas electrolytic corrosion is caused by an external source of current – often a leakage somewhere.
Source: Books for Sail, website accessed 8 October 2014