Cert III Refinishing cheat sheet

Personal protective equipment for refinishing: supplied-air or cartridge respirator rated for isocyanates and organic vapours, nitrile gloves, splash goggles, and paint suits; solvent-resistant gloves are required because latex gloves absorb solvents.

Isocyanate exposure is the primary health hazard in two-pack (2K) products; sensitisation is permanent once it occurs, so mixed 2K material must be sprayed only in a booth or with supplied air.

Flash point and lower explosive limit (LEL) govern solvent handling: vapours are heavier than air and collect at floor level, so explosion-proof extraction is drawn from low level.

Ventilation rule: booth airflow must move air from the clean (inlet/filter) side across the work toward the exhaust, and filters are rated by arrestance and pressure drop; a rising pressure drop signals a loaded filter.

Film build formula: dry film thickness (DFT) = wet film thickness (WFT) x volume solids fraction. A product at 40% volume solids sprayed to 100 micrometres WFT yields 40 micrometres DFT.

Surface preparation sequence: wash with detergent to remove water-soluble contamination, then use a solvent wipe (degreaser) with two-cloth method, then abrade, then re-clean; silicones and waxes must be removed before sanding or they are driven into scratches.

Abrasive grit numbering is inverse to cut: lower grit (P80) cuts faster and leaves deeper scratches; higher grit (P400-P800) refines. Each subsequent step must remove the previous step's scratch pattern completely.

Substrate identification decides the system: bare steel needs abrasive blast plus primer; aluminium needs etching or conversion coating; galvanised steel needs a suitable primer to avoid poor adhesion; plastics need adhesion promoter and flex additive.

Sanding scratch direction rule: on bare substrate use coarse scratches at 45 degrees to the final direction, then finish parallel to the final direction so scratches do not show through topcoat.

Viscosity reduction follows the thinner addition rule: add thinner in small increments while measuring with a viscosity cup (for example a Ford No. 4 cup), because viscosity is temperature dependent and readings must be taken at the product's stated reference temperature.

Pot life is the working time after catalyst addition; a 2K product that has gelled or exceeded pot life must be discarded, since adding thinner cannot restore reacted material and will cause adhesion and gloss failure.

Recoat window rule: if the maximum recoat time is exceeded without sanding, the previous coat must be abraded to provide mechanical adhesion; solvent can no longer soften the cured film.

Orange peel correlates with atomisation and flow: high viscosity, low atomising pressure, too-fast thinner, or gun distance beyond the recommended span increase peel; reducing viscosity and closing distance improve flow.

Runs and sags occur when wet film exceeds the coating's sag resistance; causes include over-thinning, too-slow passes, too-close gun distance, or excessive wet film per coat.

Blistering and pinholing usually trace to trapped solvent or moisture: insufficient flash-off between coats, high humidity with moisture-sensitive products, or contaminated air lines without a dryer/coalescing filter.

Colour matching steps: identify the variant or alternate colour for the vehicle, spray a spray-out card, compare under a controlled light source (for example D65 daylight), then check metamerism by viewing under a second light source.

Metamerism is a match under one light source that fails under another; it is caused by pigment differences, so a true match requires the same pigment system, not just a similar reading from a spectrophotometer.

Blend panel technique: apply basecoat to the repair area, then fade the colour into adjacent panels and clear the whole panel edge to edge, so the eye cannot find a colour boundary.