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No matter how advanced or expensive a coating system is, poor surface preparation will lead to coating failures.
Avoid the costly consequences! While requirements can differ from project to project, here is a general guide to surface preparation:
1. Remove Old or Damaged Coatings
Dry abrasive blasting, also called sandblasting, clears away the existing coating. It also creates an ideal anchor profile for the fresh layer to adhere to.
Applying new coatings over damaged ones can cause peeling, flaking, checking, and other signs of coating failure. Restoring a metal surface to its suitable condition ( example: “White Metal” SSPC-SP 5 and NACE 1) returns the asset in the best possible condition before coating application, thereby, extending its lifespan by minimizing the risk of corrosion.
2. Get Rid of Contaminants
Removing surface contaminants enhances coating adhesion and performance. Solvent cleaning effectively eliminates light contaminants, including grease, grime, and oils. As for stubborn mill scale and rust, they may require abrasive blasting techniques to remove. Any chlorides or acids on the surface must also be neutralized before applying a fresh layer of coating.
Residues left on the surface will impair the new coating’s performance and lifespan. Moreover, note that some contaminants are invisible to the naked eye. Hiring an independent coatings inspector equipped with industry knowledge and advanced tools is necessary to detect even the smallest trace of debris and impurities.
3. Remove Loose Parts
Abrasive blasting is an effective way to remove chipping paint, flaking rust, and other loose materials from the substrate.
This step helps strengthen the integrity or bond between the substrate and industrial coating. It prevents sudden coating failure, corrosion, and contamination between the metal, coatings, and stored substances.
4. Profile the Surface
“Profiling” refers to abrading the surface before coating application. It smooths irregularities and creates a textured foundation for the coating to grip onto. The degree of roughness varies from one project to another, but in general, an accurately profiled surface boosts overall adhesion.
5. Dry the Surface
After decontaminating and clearing the surface of any loose materials, give it enough time to dry before applying coatings. Even the smallest amount of moisture can interfere with adhesion, causing delamination or blistering. Pinholes can also appear during curing, particularly when moisture gets trapped between wet-applied coatings and their surfaces.
Flash rusting, which refers to the rapid onset of corrosion on a substrate, can also occur within minutes due to moisture on bare metal surfaces. Flash rust can extend beneath newly-applied coatings. By way of comparison, rust is the equivalent of cancer for metals – it erodes and weakens structures over time. Undetected and unaddressed, it can lead to catastrophic tank failures.
To protect tank assets, use a moisture meter to check whether all surface areas have reached the appropriate dryness. If necessary, speed up drying time using heat lamps, fans, or other equipment.
Lessons Learned
As highlighted above and in our previous blog post titled, 5 Industrial Coating Mistakes and How to Protect Your Assets, surface preparation matters. By taking the time to follow this guide and hiring our AMPP Certified Coatings Inspectors to oversee every step of your project, you ensure maximum adhesion and the longest possible coating lifespan.
Contact Industrial Inspection Group at 480-993-8999 for more information on surface preparation.
