Tech Tip: Types of Pole Finishes – Powder Coat vs Galvanizing
All poles have some coating to prevent corrosion. The most common options are Powder Coat or Galvanizing.
Powder coat is mostly used on parking lot and walkway poles. This is a more decorative finish providing good corrosion resistance but not the best. The coating is applied as a powder that is baked to adhere to the pole and provide the final finish. Light pole powder coating steps are:
- Sand blast to prep the surface
- Pre-heated depending on design
- Powder is applied using an electro-static gun
- Baked to provide the final finish.
- During baking the powder melts and adheres to the pole when cool.
Almost any color and finish you can think of are available, however there are common options restricted by availability, exterior rating and cost. The most common light pole colors are Bronze, Black, White, Gray, or Green. Other common custom colors are Red, Tan, and Blue. The common finishes are Gloss and Textured. Other common custom finishes are Hammered (AKA Wrinkle) and Flat (to match older faded coatings). It can be difficult to provide an exact match to another powder coated color and finish. Even using the same powder, 2 parts coated at different times can have slightly different colors. This can be caused by variations in the mix from the powder coat manufacture, the specific heat of the material being coated, time and temperature of the oven, and even the humidity on the day of coating. Once the part is installed and, in the sun, for a month, any variances in color have faded away and will look similar.
This process applies to steel and aluminum poles. Fiberglass and composite poles have a separate coating process.
Most light poles are not coated on the inside due to the difficulty of prepping the inside of the tube. Without good prep, the powder will not adhere to the metal and is useless. Some manufactures have specialized tools to clean and coat the inside of the poles. Some installers paint the inside of the pole with an internal frame coating once installed.
Galvanizing, also known as Hot Dip Galvanizing (HDG), is the best rust preventative process available for steel poles. Aluminum poles are not galvanized because they can’t withstand the heat of the galvanizing process and do not corrode as fast as steel poles. Galvanizing is commonly seen on utility poles, large parking lot poles, and steel streetlights. The galvanizing process consists of:
- Sand blasting to remove loose corrosion.
- Acid bath cleaning to remove any contaminates.
- Pickling to prep the surface.
- Finally galvanizing where the part is dipped in a molten bath of zinc and other chemicals.
- Cleaning or finishing to remove any excess material.
This provides a Silver/Gray finish that can vary depending on how the material was protected right after galvanizing. Some are a bright silver (AKA Bright Galvanizing), and others are a dull gray discoloration caused by the material getting wet or being in a humid environment to soon after being coated. There is no structural difference in the bright or dull finishes, it is simply aesthetic.
Colored powder coat can be applied over the top of galvanizing. This process provides the best of both, the rust protection of galvanized and the decorative look of powder coat. It includes a few extra steps that takes time but is done when needed. The final powder coat finish will not last as long because the powder does not adhere to the galvanized coating as well as it does to raw prepped steel.
How long a pole will last depends on the finish but also its environment. If installed and maintained correctly a powder coated pole can last a long time. Even a galvanized pole will rust if its covered in dirt in a planter getting watered. All else the same, a galvanized pole will outlast a powder coated pole.
The best coating for the project depends on a mix of environment, pole type, expected life, lead time, and budget.