” I install powder coated hot dip galvanized 100x100x3mm SHS posts to support sails. These are then set in concrete footings. I now have had 2 separate jobs where the powder coating is “bubbling” and lifting away from the steel at the ground level. One job is in a garden bed the other is in a sandstone style poured paving. I would like to know if this problem can be fixed and why it is happening. I would also like to know how to stop it from recurring and how to get the finish back to its original condition.”
“You should check the back of the paint chips that have fallen from the posts. I’ll bet that the paint chips have zinc galvanizing on the back side, proving that the galvanizing failed and took the powder coating with it. Hot dipped galvanizing is a great corrosion resistant material and hot dipping is the easiest way to apply this material. The only problem is the galvanizing delaminates from the steel surface over time. Often the steel is still covered with some galvanizing that is still intact.
If this is the case, just use a liquid paint to cover the exposed galvanizing. To prevent this from occurring in the future you should use a paintable grade of galvanizing (i.e. electroplating). This way the galvanizing will stay intact on the steel surface. The powder coating will then adhere to a solid surface that will not flake off over time. Remember, powder coating, like all paints, is only as good as the surface it is applied to. If that surface is unstable, the coating will not perform.”