ITI Mechanic Auto Body Painting (AITT Theory) common mistakes
ITI Mechanic Auto Body Painting (AITT Theory) · Understand the traps and how to avoid them.
Treating isocyanate hardeners as a skin-irritation issue only, so candidates answer that nitrile gloves and a dust mask are adequate protection when spraying 2K primer or clearcoat.
Isocyanates are sensitizers that can cause occupational asthma, and the hazard is the aerosol and vapour, not just skin contact. Candidates who have only seen gloves and a dust mask in a small shop assume that is the whole control set, and they confuse a particulate filter with a vapour cartridge.
What to do instead
Learn the control hierarchy as a set: supplied-air or air-fed respirator with the correct cartridge for the product, full skin coverage, local exhaust or booth ventilation, and health surveillance where required. Be able to state that a dust mask does not stop isocyanate vapour and that sensitization can occur at low exposure. Practise matching each product class (2K isocyanate, solvent-borne, waterborne, polyester filler) to its specific PPE and ventilation requirement.
Answering that a surface is ready for primer because it feels smooth to the hand, without checking for wax, silicone, or invisible contamination.
Tactile smoothness is a poor proxy for cleanliness, and candidates under time pressure skip the wipe-down sequence. They also reverse the order, wiping with a solvent before washing with water-based degreaser, which spreads contaminants instead of removing them.
What to do instead
Memorize the sequence: wash with a water-based degreaser and rinse, dry, then wipe with the appropriate solvent prep cleaner using a wet-then-dry cloth technique, and change cloths frequently. Know that silicone contamination causes fish eyes and craters and that it can come from polishes, protectants, and even the shop air. Practise explaining why a smooth-feeling panel can still fail adhesion.
Mixing primer, sealer, or clearcoat by eye or by 'thin to spray' rather than by the stated ratio, and not accounting for pot life once catalysed.
Candidates memorize ratios as isolated facts but do not connect them to the consequences: wrong ratio changes cure, gloss, adhesion, and sandability, and expired pot life causes solvent entrapment, loss of gloss, or a coating that never hardens. Shops sometimes mix by feel, and candidates copy that habit.
What to do instead
Learn to calculate by volume and by weight for each product family, and be able to state the effect of too much and too little hardener or reducer. Tie pot life to temperature: warmer shop, shorter pot life. Practise a worked example where you scale a batch to the panel size and check the ratio, then state what happens if the batch is used past its pot life.
Setting gun pressure, fluid flow, and fan pattern by copying a number from a manual without adjusting to the actual product, temperature, and distance, then blaming the product for runs or orange peel.
Candidates treat spray settings as fixed constants rather than variables that interact. They also confuse inlet pressure with pressure at the cap, and they do not test the pattern on a test panel before committing to the repair.
What to do instead
Learn the cause-and-effect chain: too close or too slow gives runs and sags; too far or too fast gives dry spray and roughness; too much fluid or too little atomizing air gives orange peel; a split or heavy-centred pattern points to a dirty or damaged cap or needle. Practise stating a corrective action for each defect rather than a single 'correct' setting, and always describe testing the pattern on a test card first.
Judging a dent repair as finished after the filler is shaped, without checking the surface with a guide coat, a straightedge, or a hand-feel pass under raking light.
Filler can look flat under normal shop lighting while still being high or low. Candidates stop when the filler feels smooth and skip the verification steps, and they do not account for the fact that primer and topcoat will not hide a shape error.
What to do instead
Build a routine: block-sand with a guide coat, check with a straightedge and by hand across the repair in two directions, and inspect under raking light before priming. Know that high spots show as shiny areas when block sanding and low spots hold guide coat. Practise describing how you would prove a repair is level before moving to primer.
Choosing a primer or sealer without matching it to the substrate and the topcoat system, for example using an etch primer on bare aluminium or applying a sealer over a substrate that needs an isolator.
Candidates learn product names but not the compatibility matrix. They do not connect substrate type (bare steel, galvanized, aluminium, plastic, existing cured finish, body filler) to the required pretreatment and primer chemistry, and they miss that some substrates need a barrier coat to stop solvent attack or bleed-through.
What to do instead
Build a substrate-to-product table in your own words: what pretreatment each substrate needs, which primer bonds to it, and what must not go directly over it. Learn the purpose of an isolator/sealer over unknown or bleeding finishes and over body filler. Practise answering 'what would you put on this substrate and why' for at least six substrate types.
Diagnosing a finishing defect by its appearance alone and naming a single cause, when the same defect (for example solvent pop, blushing, or mottling) has several possible causes across product, environment, and technique.
Candidates memorize a one-to-one defect-to-cause list and then cannot handle questions that describe conditions rather than a picture. They also ignore environmental variables such as humidity, shop temperature, and flash time between coats.
What to do instead
Learn each major defect as a differential: list at least three plausible causes and the evidence that separates them. For example, blushing points to moisture in the air line or high humidity; solvent pop points to excessive film build or too-short flash; mottling points to metallic application technique. Practise reading a scenario and stating the most likely cause plus the check that would confirm it.
Treating metallic and pearl colour matching as a formula lookup, then delivering a panel that matches under the booth light but not in daylight, or a panel that is the right colour but the wrong flop.
Metallic and pearl colours change with viewing angle, and candidates underestimate the effect of gun distance, air pressure, reducer speed, and application technique on flop and face colour. They also skip the spray-out card comparison and blend-panel planning.
What to do instead
Learn the full matching process: identify the variant with a spray-out card, compare under the correct light sources including daylight, adjust application variables one at a time, and plan a blend into adjacent panels rather than a butt match. Know that dry spray and gun distance shift metallic orientation. Practise explaining why a colour can be right at one angle and wrong at another.
Giving an estimate as a single lump sum without separating parts, labour, materials, and refinish operations, and without documenting pre-existing damage or the customer's authorization.
Candidates focus on the repair and treat the paperwork as an afterthought. They do not connect an undocumented estimate to disputes, supplements, and unpaid work, and they do not know that hidden damage found after disassembly requires a documented supplement and customer approval.
What to do instead
Learn the structure of a repair order and estimate: identification, damage assessment, operations by panel, refinish time, parts, materials, and a clear statement of what is included and excluded. Practise writing a supplement for hidden damage and describing how you would walk the customer through the repair and the warranty at handover. Emphasize photographs and signed authorization before work proceeds.
Handling and storing waste solvent, mixed leftover paint, and spray booth filters as ordinary rubbish, or pouring solvent-borne waste down the drain.
Candidates do not connect shop activities to environmental regulation and often assume small quantities are exempt. They also do not distinguish hazardous waste streams, and they ignore that catalysed leftover paint may need to cure before disposal.
What to do instead
Learn the waste streams and their handling: solvent waste in closed labelled containers, waterborne waste kept separate, filters and masking as contaminated waste, and no discharge to drains or stormwater. Know that mixing waste streams can make disposal harder and that local rules set the details. Practise describing a compliant routine for a booth filter change and for leftover catalysed clearcoat.