Paint drying on its substrate is a chemical process:
Solvents are dissolving, adhesives are adhering, and pigments are pigmenting. Once the process is done, the paint provides a thin, protective layer to the equipment it is sticking to, sort of like a synthetic skin. This coating protects equipment from environmental assailants that slowly wear away at metal — like moisture and salinity. Industrial companies take the time and spend the resources painting their outdoor equipment to prolong its life-expectancy. They need to be certain that the paint they are using is going to adequately protect their equipment for a long time. Testing laboratories, like Applied Technical Services, help them establish the effectiveness of their protective measures by performing paint adhesion testing.
About Coatings and Adhesion
A paint’s adhesion is a quantifiable characteristic that describes how well it bonded to its substrate. This number can vary because different paints and different substrates will have different chemical makeups and physical attributes, thus interacting with each other differently. For quality control purposes, many clients are interested in discovering the failure point of their coating — or the amount of force needed to cause the paint to separate from the substrate. ATS’s technicians establish this through one of a few testing methods, chosen as appropriate for the circumstances.
These tests are repeated multiple times in different, simulated climates to control for the substrate expanding or contracting due to varying temperatures; these conditions can also affect the adhesion of a paint to its substrate. Although other methods of paint adhesion testing do exist, the following list reflects the most common practices:
Test Methods and Standards
- ASTM D4541 and ISO 4624 standard testing methods
- Quantitative
- Could be performed on-site
- Measures how much load is needed to remove the dolly (adhesive layers and all)
- Can stop at a predetermined value instead
- Exerts tensile stress as opposed to shear stress
- Means these results do not measure the same value as the other two methods
- More variables to consider than in other tests
- Used only on coatings covering flat surface, but no limitations on what material of coating
- ASTM D2197 standard testing method
- Quantitative
- Requires laboratory staging
- Cannot be done on-site
- May only be used on flat samples
- Used for lacquers, varnishes, coatings, and paints
- ASTM D3359 standard testing method
- Qualitative
- Quick
- Results are judged on either a 0–5 scale or pass/fail criteria
- Can use knife to pry off paint instead of pulling off with tape
- Used specifically for coatings and paints