ITI Mechanic Auto Body Painting (AITT Theory) flashcards

34 cards. Read the term and the definition here. The deck at the top of this page is optional.

Isocyanate sensitisation

Repeated exposure to isocyanate hardeners can make the immune system react to very low concentrations, causing occupational asthma. Once sensitised, the worker may be unable to continue spray painting.

Grade D breathable air

Compressed air quality standard for supplied-air respirators. It requires a dew point of 3 °C or lower, no detectable oil mist, and carbon monoxide monitoring before the air reaches the mask.

Spontaneous combustion of rags

Solvent- and oil-soaked rags can self-heat and ignite without a spark. Store them in a self-closing metal bin or sealed water container and never in general waste.

Class B fire

Fire involving flammable liquids such as thinners, solvents, and paint. Extinguish with foam, dry powder, or CO2; a water jet spreads the burning liquid.

Whip-check hose safety

A cable or restraint fitted to air tool hoses that stops the hose whipping if a coupler fails. It is required on compressor lines and spray equipment in the workshop.

Grit progression for refinish

Coarse to fine sequence: 80–120 grit for stripping, 180–240 for primer surfacer, 320–400 for sealer prep, 500–800 for blending topcoat edges. Each step removes the previous scratch pattern.

Guide coat

A thin contrasting mist applied over primer or filler. Sanding reveals low spots and scratches as dark areas that remain, showing where more levelling is needed before topcoat.

Silicone contamination

Oil or silicone on the substrate causes fish-eye craters in the paint film. It is removed with wax-and-grease remover using a wet cloth followed by a dry cloth.

Galvanised steel preparation

Do not blast or heavily grind zinc coating. Clean the white oxide, then apply a zinc-compatible etch or wash primer to obtain adhesion before further coats.

Dew point rule

Substrate and shop temperature must be at least 3 °C above the dew point before coating. Otherwise condensation forms under the film and causes blistering or poor adhesion.

Pot life

The working time after hardener is added to a catalysed product. It shortens as temperature rises, roughly halving for every 10 °C increase, and expired material must be discarded.

Mixing ratio by volume

Catalysed paints are mixed as parts base, hardener, and reducer by volume using a graduated cup, unless the technical data sheet specifies mixing by weight.

Drop coat

A final light coat applied at reduced pressure and greater distance over metallic basecoat. It aligns aluminium flakes evenly so the face colour appears uniform.

Colour variant

A plant-specific shade of one OEM colour code. The correct variant is chosen by spraying a test card and comparing it with the vehicle under daylight and booth lighting.

Reducer selection

Fast reducer suits small spot repairs and cool conditions, medium for general work, slow for large panels or hot booths. The wrong speed causes dry spray or solvent popping.

HVLP transfer efficiency

High-volume low-pressure guns deliver more material to the panel and less as overspray than conventional guns, because lower air pressure reduces bounce-back and fog.

Spray overlap

Successive gun passes should overlap by about 50 % for uniform coverage, or 75 % for clearcoat and high-solids products to avoid striping and thin bands.

Split spray pattern

A fan with a heavy centre or two separated lobes indicates a clogged air cap, worn needle, or incorrect fluid tip. Clean or replace parts before spraying.

Booth face velocity

The air speed through the booth working area, typically 0.2–0.5 m/s in a downdraft booth. Clogged filters reduce it and increase overspray and dirt contamination.

Body filler thickness limit

Polyester filler is for cosmetic levelling, generally no more than 3–6 mm thick. Deeper damage must be straightened or the panel replaced before filling.

Filler catalyst ratio

Polyester filler hardener is measured at the label ratio, commonly about 2 % by weight. Too little leaves soft, clogging filler; too much makes it brittle and porous.

Stud welder dent pulling

A stud welder fuses pins to bare metal so a slide hammer can pull a dent outward. Controlled force avoids over-stretching the metal and creating oil-canning.

Heat shrinking

Stretched metal is restored by heating a small spot to dark red and quenching, or by using a shrinking hammer. It restores panel tension and removes oil-canning.

Etch primer

A thin acid-bearing primer for bare steel and aluminium, usually 10–20 µm. It must not be applied over body filler or existing paint.

Epoxy primer recoat window

The time range in which the next coat bonds chemically to epoxy primer. If the window is exceeded, the surface must be sanded before recoating.

Wet to dry film thickness

Dry film equals wet film multiplied by volume solids divided by 100. A 50 % solids product sprayed at 100 µm wet gives 50 µm dry.

Sealer function

A sealer coat applied before basecoat locks the substrate, equalises absorption, and blocks solvent bleed from underlying layers for uniform topcoat holdout.

Solvent pop

Small blisters or pinholes caused by trapped solvent escaping through a partly cured clearcoat. Correct flash-off times, reducer speed, and film thickness prevent it.

Orange peel

A textured surface resembling citrus skin, caused by poor atomisation, high viscosity, or a fast gun pass. It is corrected by sanding and polishing or by adjusting gun setup.

Fish-eye

Circular craters in the paint film caused by silicone or oil contamination on the substrate or in the air line. Clean the surface and fit an oil and water separator.

VOC content limit

A regulatory cap on volatile organic compounds in refinish products, for example 420 g/L for clearcoat. The product data sheet states the compliant value.

Waste segregation

Separate waste solvent, waste paint and catalysed material, empty metal containers, and contaminated rags. Each stream has its own licensed disposal route and records.

Paint quantity formula

Litres of mixed paint equals area in m² multiplied by dry film in µm, divided by volume solids percent times ten. Add 20–30 % for loss.

Three-panel blend rule

A repair on one panel usually requires blending into the two adjacent panels to match metallic colour, so the estimate must include refinish time for all three.