Core Units: Safe Practice, Surface Preparation and Coatings Fundamentals
What the core units cover
Core units establish the non-negotiable foundation of automotive refinishing: work health and safety, workplace communication and documentation, environmental and waste obligations, surface preparation, masking, colour matching, and application of undercoats and topcoats. Questions test whether you understand why a step exists, not just the order of steps.
Concepts you must know
- Hazard control hierarchy: elimination, substitution, engineering controls (spray booth extraction, ventilation), administrative controls (SDS, training, rotation), then PPE as the last line of defence. A question offering "wear a respirator" as the best control for isocyanate exposure is usually a trap - engineering controls rank higher.
- Isocyanates and two-pack products: sensitisation is cumulative and irreversible; respiratory protection must match the SDS, and fit testing is required.
- SDS and labelling: know the sections used to find first-aid, handling and disposal information.
- Substrate identification: steel, aluminium, galvanised, plastic, and OEM vs. cured refinish each demand different abrasives and primers. Feather-edging, sanding scratch progression (e.g. 80 → 180 → 320/400 grit), and cleanliness between grades prevent scratch swelling.
- Contamination traps: silicones, oils, and fingerprints cause craters and poor adhesion; wax and grease remover must be wiped on and off with separate cloths, not allowed to evaporate.
- Masking: correct tape for the surface and cure temperature; hard edges and bridging are common question traps.
- Mixing ratio, pot life, and induction time: measuring by volume, not guesswork; adding thinner beyond the technical data sheet is a defect waiting to happen.
Worked example / rule of thumb
A panel is repaired with body filler, then primed and topcoated, and the topcoat sinks into sanding scratches. Rule of thumb: each abrasive grade must remove the scratches of the previous grade, and the primer must be compatible with the topcoat's solvent strength. The fix is not more topcoat - it is finishing the substrate at a finer grade and using a sealing primer.
Exam traps
Read for the first or most effective control, distinguish "check" from "correct", and never accept a shortcut that bypasses the technical data sheet.