Powder Coating over Hot-Dipped Galvanized steel is a duplex system that gives the corrosion-resistant benefits of galvanization, with the added protective layer and color selection choices of powder coating.
This two-part finish system improves the lifespan of the steel, but it also comes with a few considerations. Please read through the following sections to familiarize yourself with the process and what to expect of the finished product.
Final Finish: What to Expect
Rough, Textured Surface: While the maintenance benefits of this two-part finish can be great, it does result in a rougher and more textured finish surface than a standard, powder coat only finish.
Imperfections: The protection of the galvanized steel can impact the adhesion of the powder coat finish, which may result in a semi-rough surface with minor imperfections, flaking, etc. These imperfections are expected (see examples). The hot-dipped galvanized base layer is doing its job and we advise against performing any “repairs.”
The Process
- Initial Wash: The steel is put through an initial, multi-stage wash and pre-blast inspection to catch and remove oil, grease, and other coatings with impeding contaminants.
- Acid Clean: An acid cleaner is used to remove oxidation and create a light etch in the surface for best adhesion. Members are then set to dry.
- Galvanizing Bath: Members then go into a tub of molten zinc to apply the corrosion-resistant base layer (hot-dipped galvanization) and members are hang-dried at an angle to allow all residual liquid galvanization materials to drain out until cool.
- Grinding: After cooling, members will have larger build-up and bumps grinded off.
- Outgassing: Zinc coating traps moisture and air and members must be pre-baked to drive out trapped gasses, oils, moisture, and other volatiles.
- Pre-Powder Coat Clean: Members are then brush-blasted to push the top galvanizing layer over to expose a fresh layer of zinc. This stops the galvanized layer from pushing through the final, top layer of powder coat finish.
- Pre-Powder Coat Inspection: Any defects in the galvanization finish are inspected and addressed before proceeding to powder coating.
- Powder Coating (Primer): Members are primed with a minimum of 1.5 mils before being gel-coated in the oven.
- Powder Coating (Topcoat): After cooling, a minimum of 1.5 mils topcoat of TGIC polyester powder coating is applied as the final finishing layer (colors to be selected from standard color chart).
- Final Inspection: All materials inspected to meet 100% coating, proper cure, film thickness, and impact resistance. Touch-up is handled on any pieces that did not pass inspections.
- Packaging: Members will be wrapped in foam, cardboard, and saran wrap to protect the finish all the way to the job site.