Coating Application and Materials
Materials and their logic
Marine coating systems are layered for a reason. Understand the roles of primers (anticorrosive, often zinc-rich or epoxy), intermediate coats (barrier, build), and finish coats (UV, color, chemical resistance). Know the common generic types and their strengths and weaknesses: epoxy (excellent barrier, chalk under UV), polyurethane (UV-stable topcoat), zinc-rich primers (galvanic protection, sensitive to overcoating), and antifouling (biocide release, incompatible with some primers). Know that mixing, induction time, pot life, and recoat windows are material-specific.
Application concepts
Understand application methods: airless spray (most common for large areas), brush and roller (stripe coats, edges, welds), and plural-component spray for fast-cure materials. Know that stripe coats are applied to edges, welds, cutouts, and back-to-back angles before full coats because spray tends to thin on these features. Understand wet film thickness (WFT) and its relation to DFT: DFT = WFT × volume solids fraction. Know that overcoating outside the recoat window requires surface preparation (sanding/solvent wipe) to ensure adhesion; within the window, a solvent wipe may suffice.
Traps in questions
Common traps: assuming more coats always means more protection (system design matters); assuming WFT equals DFT (it does not - volume solids apply); and confusing pot life with recoat window. Another trap is applying a coating below its minimum application temperature even though ambient air is warm - substrate temperature governs.
Worked rule of thumb
A coating with 60% volume solids applied at 200 µm WFT yields about 120 µm DFT (200 × 0.60). If the specification requires 150 µm DFT, you need ~250 µm WFT - verify with a comb gauge during application, not after.