ITI Mechanic Auto Body Repair (AITT Theory) common mistakes
ITI Mechanic Auto Body Repair (AITT Theory) · Understand the traps and how to avoid them.
For 2K automotive paint or primer spraying, the candidate selects a disposable dust mask or a simple charcoal half-mask as adequate respiratory protection.
They memorise 'wear a mask when painting' as a single PPE rule and do not link two-pack isocyanate paints to vapour/aerosol exposure that a particulate dust mask cannot control.
What to do instead
Learn the PPE decision by product type: 2K isocyanate-containing materials require an approved air-supplied or air-fed respiratory system, skin and eye protection, and a ventilated spray booth; a dust mask is only for dry sanding dust.
When selecting a hacksaw blade for cutting thin sheet or tube, the candidate chooses a coarse blade because it 'cuts faster', then snags or tears the workpiece.
They remember tooth pitch as a speed choice rather than a material-thickness choice, so they ignore that coarse teeth catch thin sections.
What to do instead
Match pitch to section: use fine pitch, such as 32 TPI, for thin sheet and tube walls; use coarser pitch, such as 18–24 TPI, for thick solid sections; keep at least two or three teeth in contact with the work.
The candidate reads a vernier calliper or micrometer directly without first checking zero error, or reads the vernier scale at an angle and records the wrong value.
They treat the instrument as 'always correct' and practise only the reading procedure, not the zero-check and parallax-control steps that precede a valid measurement.
What to do instead
Before measuring, close the jaws or anvils and confirm zero; if there is zero error, apply it with the correct sign, subtracting a positive error and adding a negative error. Read with the scale square to the eye and repeat the measurement.
The candidate repairs a stretched or high-crown dent by applying thick polyester body filler over paint or rust instead of metal-finishing and shrinking the panel first.
They confuse filler with a structural repair material and skip hammer-and-dolly work because filler is quicker and hides the damage visually.
What to do instead
Remove paint and rust to bare steel, identify stretched metal, shrink and planish the crown with hammer and dolly or a shrinking method, then apply filler only as a thin finishing coat over a properly prepared, stable surface.
The candidate states that brazing and soldering are separated only by the type of torch used, or gives brazing a working temperature below 450°C.
They memorise joining processes as shop routines rather than by filler melting temperature and base-metal melting point.
What to do instead
Use the temperature definition: soldering uses filler melting below 450°C; brazing uses filler melting above 450°C but below the melting point of the base metals; the heat source does not define the process.
During a chassis or frame alignment question, the candidate checks only one diagonal measurement, or measures to random body points, and concludes the frame is straight.
They reduce alignment to 'diagonals must be equal' and do not use manufacturer datum points, centreline and control dimensions that reveal sway, sag or mash.
What to do instead
Use the maker’s datum and control-point dimensions, compare left/right symmetry about the centreline, check multiple diagonals and height readings, and distinguish damage types before recommending pulling or replacement.
The candidate identifies a plastic bumper by appearance and then uses any available plastic welding rod, without checking the ISO material code or doing a compatibility test.
They assume all thermoplastics weld the same way and skip substrate identification because the repair looks simple.
What to do instead
Identify the substrate from the ISO code or a controlled burn/compatibility test, select the matching welding rod and temperature, and test the weld on a scrap piece before repairing the component.
The candidate mixes a 1K base coat with hardener, or adds reducer to a 2K clear coat without checking the technical data sheet ratio and pot life.
They generalise 'paint always needs hardener and thinner' and do not distinguish 1K lacquer/base coat from 2K products that require a specific activator and mix ratio.
What to do instead
Read the product technical data sheet for each coat: mix by volume at the stated ratio, use the specified reducer or activator, observe pot life and induction time, and do not add hardener to a 1K base coat.
For a bonded windscreen, the candidate specifies silicone sealant or installs the glass and lets the vehicle go immediately without observing the urethane safe drive-away time.
They treat windscreen adhesive as a general-purpose sealant and overlook that bonded glass contributes to body stiffness and occupant retention.
What to do instead
Use automotive polyurethane windscreen adhesive with the correct primer and bead profile, follow the maker’s curing and safe drive-away times, and do not substitute silicone or non-structural sealant.
When diagnosing a battery drain, the candidate connects an ammeter in parallel across the battery or pulls fuses at random without allowing modules to enter sleep mode.
They confuse voltage measurement with current measurement and do not know that modern vehicles draw normal closed-circuit current until modules sleep.
What to do instead
Measure parasitic draw with a clamp meter or a correctly rated ammeter in series after all modules have slept; compare with the maker’s limit, then isolate the circuit by voltage-drop or fuse removal and reconnect safely.