1. Remove contaminants
The first objective of surface preparation is to remove surface contaminants that will affect the performance of a coating. These contaminants can include:
Oil and Grease – Prevent good coating adhesion and must be completely removed.
Salts – Increase moisture penetration through the coating and accelerates the rate of corrosion.
Dust and Dirt – Prevent the application of a smooth, uniform fi lm thus weakening the adhesion of a coating to the substrate.
Rust – Often cannot be penetrated by most coatings resulting in uneven fi lms with exposed metal where corrosion can take place.
Rust scale and Mill scale – Cannot be penetrated by most coatings and will eventually break free from the substrate taking any coating with it. More about Mill scale.
Old Coatings – May lift from the surface when over coated causing peeling or delamination.
2. Remove imperfections
The second objective is to remove surface imperfections over which it is difficult to obtain adequate coating dry fi lm thickness (thin layer coatings). Some of these are:
- Weld Spatter
- Sharp Edges
- Burrs
- Slivers
- Laminations
- Pits
- Porosities
- Crevices
3. Create the required surface profile
The third objective of surface preparation is to provide an “anchor pattern” or “surface profile” which improves the mechanical bonding of a coating to the prepared surface by increasing the surface area.
