Metal finishing Q&As since 1989

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Powder Coating

2002

I have a few questions regarding a powder coated fence:

1. Will a continuous spray from lawn sprinklers with hard water cause a powder coat finish to degrade or the steel underneath to rust?

2. Will a continuous spray from lawn sprinklers with hard water cause welded joints that are powder coated to rust?

3. Is it a correct assumption that the steel and joints will not rust? Is the powder coat a barrier from the water?

Lee J. Andrews
contractors - Phoenix, Arizona, USA

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First of two simultaneous responses --

Lee,

In part your assumption is correct, powder coating will protect the substrate from water ... if .... the cleaning and pre-treatment of the substrate is correct and the application and curing of the powder coating is correct and finally if the right powder coating chemistry is used.

Drew Devlin
- Lincolnshire
2002

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Second of two simultaneous responses -- 2002

Hi Lee,

1. Quite possibly, yes.
2. Quite possibly, yes.
3. No, it is a bad assumption. Yes, powder coatings act as a barrier, but only in limited fashion.

George Gorecki
- Naperville, Illinois

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And, yes, usually the weld area will be attacked first, both because it is a bit harder to pretreat and coat, and because the stresses make the weld area electrochemically anodic to the rest of the metal.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2002

Your finish is dependent on the pretreatment process. Blasting of the welds and a iron phosphate pretreatment will extend your life product life.

Steve Mossige
- Dallas, Texas
2002