Pretreatment is the term applied to the process of preparing a surface to receive powder coat.  Powder can be sprayed over bare metal with no special pretreatment and initially look beautiful, and if you are paying $100 to powder coat your Harley frame this is probably what you are getting.  Without proper pretreatment, however, the powder will chip and corrode easily.

Pretreatment involves the stripping of any existing corrosion or coating, the cleaning and degreasing of the bare metal, and the creation of a surface finish adequate for a powder coat.  The objective is to leave a clean and slightly rough surface profile as an anchor pattern for the powder to adhere to.  Some people refer to this profile as “tooth” because it effectively bites into the powder coat to mechanically interlock the coating and substrate.

The ideal anchor pattern to powder coat steel is created either mechanically by abrasive blasting, or chemically with a phosphate coating.  Abrasive blasting, although necessary for removing rust or old coatings, is expensive and very aggressive.  Blasting can easily put a profile in steel which is rougher than the subsequent powder coat would be thick.   To get the best powder coat possible after abrasive blasting, manual sanding is sometimes required to knock the peaks off the blasted surface profile.

For steel which is new or has been chemically stripped, a phosphate chemical can be used in place of (or in addition to) abrasive blasting to create an ideal anchor pattern for powder coating steel.  The phosphate is applied as a weak acid and first etches (or “pickles”) the metal.  Chemical engineers refer to this process as “activating” the surface, after which a chemical reaction takes place between the steel and phosphate to produce a phosphate oxide layer that has both a well-suited profile for powder coat as well as a chemistry which helps inhibit substrate corrosion.

The powder coat pretreatment process may include washing, degreasing, chemical stripping, abrasive blasting, phosphate coating, rinsing, and high temperature out gassing.  Seattle Powder Coat has the equipment, permits, and process knowledge to do each of these steps.

Stools Coated Antique White

Rusty Stools Prior To Stripping And Powder Coating