Weathering of a coating in which ultraviolet light degrades the resin at the surface and frees pigment as loose powder that rubs off on a finger or cloth. Epoxies chalk heavily in sunlight, which is why outdoor epoxies get a polyurethane or other UV-stable topcoat. Chalk is rated with tape or cloth tests and must be washed off before overcoating, or the new paint bonds to dust.
Old epoxy on the tank is chalking bad, pressure wash it before the urethane goes on or it'll peel.
Also heard as
- chalk
Related terms
Zinc-rich primer
Primer loaded with zinc dust that protects steel galvanically as well as acting as a barrier.
Pull-off adhesion test
Test that glues a dolly to a coating and pulls it off to measure how strongly the coating sticks.
Tooth
Painters' word for the roughness on a surface that gives a coating something to grip.