Why Does Powder Coating Flake Off, Bubble, Chip or Crack?
Powder coatings on metal were first used commercially in the 1960’s to reduce the excessive use of toxic chemicals. Now, the powder coating process is relatively simple and it is widely used as an environmentally friendly alternative to liquid coating. It produces a durable and exceptional looking finish if applied properly, but like all paint, eventually it will fail. Why does powder coating flake off, bubble, chip or crack?
Powder coating will flake off, bubble, chip or crack sooner than it should for a multitude of reasons:
1. Composition of the Substrate
The powder coating method consists of layers where each stage of the process can negatively affect the next layer. There could be problems with the metal surface and this substrate may affect the pre-treatment and finally the powder coating itself.
2. Rough Metal Surface
The surface of any substrate is bound to vary in smoothness. Blasted metal or any sharp edges must either be completely smoothed out or a thick layer of coating must be applied in order for it to resist corrosion. Sometimes, even microscopic protrusions may not be fully covered even if thick layers of coating are applied.
3. Metal Edges or Corners are not Coated Properly
Generally, corrosion starts on the edge of a panel rather than in the middle of it. Metal edges can be particularly sharp and need to be ground down properly so that there are no small tips poking through the powder coating. Corners may be hard to reach and if they are not coated thoroughly they are susceptible to corrosion.
4. Incorrect Pre-Treatment
When metal objects are hung for their pre-treatment rinse, some sediment may accumulate at the bottom of the items and the powder coating often fails in places where this sediment has dried onto the surface. There may also be a lack of pre-treatment or the pre-treatment chemicals are not used correctly. Some parts of a metal surface may be more difficult to penetrate with pre-treatment than others, so extra care may not have been taken with edges, corners and recesses.
5. Using the Wrong Powder for Coating
Choosing an inappropriate powder coating is a common mistake because the environment the architectural metal work is in isn’t always taken into account. The surrounding conditions are more important for exterior metal than for products that remain indoors.
6. Powder Coating is too thick or too thin
Failures in powder coating can also stem from how it is applied. If the powders are applied too thinly, the patchy surface will not have full protection and could lead to corrosion. If a layer is too thick, flexibility will be limited. Sometimes, multiple layers are applied and each one has to be perfect for the optimal performance of the coating as a whole.
7. Inadequate Curing
Even if the substrate is correctly pre-treated, the powder coating may breakdown if it is not cured adequately. Powder coating takes a certain amount of time at a particular temperature to cure properly and powder that is under-cured will not be the most durable even though it may appear intact. Colour degradation and a lack-lustre finish may be an indication of improper curing.
8. The Wrong Temperature
The baking cycle is an extremely important part of the powder coating process. The metalwork has to reach the recommended temperature for a suggested amount of time. That means all of the coating uniformly, not just the surface.
9. Poor Quality Materials
Sometimes coating deteriorates if inferior ingredients are used with excessive amounts of filler material.
10. The Environment
Powder coating breaks down more quickly if it is outside in harsh environments. Extreme temperatures, weathering, UV light and collisions all impact on the coating’s integrity. Water, dirt and / or salt particles can find their way into the smallest crevice and insidiously corrode the paint by migrating under the coating. This results in an imperfect powdered finish.
No paint lasts forever, but we can repair powder coating that has failed, so that metalwork looks as good as new again.