ITI Mechanic Auto Body Painting (AITT Theory) key terms

The lowest temperature at which a liquid releases enough vapour to ignite briefly when a flame is passed over its surface. Solvents with low flash points need careful storage and ignition control.

The mass of volatile organic compounds released per litre of a coating as it cures. Regulations cap VOC levels, so painters must choose compliant products and measure mixing ratios accurately.

An allergic reaction that develops after repeated exposure to isocyanate hardeners, causing asthma-like symptoms that can become permanent. It requires supplied-air respiratory protection and strict enclosure controls.

A breathing apparatus that delivers filtered air from a remote compressor or cylinder to a full facepiece. It is mandatory for spraying isocyanate hardeners because cartridge masks do not remove these vapours.

The controlled movement of filtered air through a booth, usually measured in metres per second at the filter face. Correct airflow carries overspray away from the painter and prevents contamination settling on wet films.

Airborne paint droplets that miss the repair area and settle on surrounding surfaces or dry as dust. It causes roughness and adhesion problems, so masking and booth airflow must control it.

Determining what material lies beneath the surface, such as steel, aluminium, plastic, or galvanised panel. The result dictates which abrasives, primers, and adhesion promoters are safe to use.

A gradual taper created by sanding so a repaired area blends smoothly into the surrounding original finish without a visible step. Poor feather edging shows through topcoat as a ring or shadow.

A thin contrasting dust or mist coat applied over primer or filler so low spots and scratches become visible while sanding. It is sanded away completely once the surface is level.

Sanding with a rigid or semi-rigid backing pad to level filler and primer rather than following the contours of low spots. It reveals high spots and prevents waviness in the final finish.

The scratch pattern left by an abrasive, described by grit rating and depth. Coatings need a specific profile to key mechanically, and too fine or too coarse a scratch harms adhesion.

A resin-impregnated cloth used to lift dust and loose particles from a panel immediately before coating. It reduces nibs and contamination but must not leave residue on the surface.

A two-component polyester paste used to rebuild shallow dents and level uneven panels before priming. It must be applied over a properly prepared, clean substrate and never used to bridge rust or structural damage.

A fine, fast-setting filler used to fill pinholes, sanding scratches, and minor imperfections over primer or cured filler. It is not a substitute for structural filler on deep damage.

A tiny void or air bubble in filler or primer that shows as a small crater after sanding and painting. It is filled with glaze putty or a high-build primer before topcoat.

A technique using levers and glue tabs to push or pull shallow dents out without disturbing the original finish. It works best on accessible, gradual dents where the paint is not cracked.

A pigmented undercoat that builds film thickness and fills fine sanding scratches to create a uniform base for topcoat. It is sanded smooth and may need a sealer coat over it.

A thin, non-sanding coat applied over primer or old finish to prevent solvents and pigments from bleeding through and to give uniform topcoat holdout. It is often tinted to match the topcoat.

A specialised tie-coat applied to difficult substrates such as plastics or bare aluminium to improve bonding of subsequent coatings. It must match the substrate and be applied at the specified film thickness.

Applying one coat over another while the first is still wet or only partly flashed off, allowing both to cure together. It saves time but requires strict attention to flash times and film build.

The proportion of base, hardener, and thinner specified by the manufacturer, measured with graduated cups or a mixing stick. Incorrect ratios cause poor cure, gloss loss, or premature failure.

The usable working time of a mixed two-component product before it thickens or gels. Exceeding pot life causes poor flow, weak cure, and spray gun clogging.

The reactive component, usually an isocyanate or peroxide, that cross-links a base resin and converts it from liquid to a cured film. Its ratio and mixing quality determine final film properties.

A solvent blend added to a coating to adjust viscosity for spraying, chosen to suit ambient temperature. Wrong reducers cause dry spray, runs, or solvent popping.

A measure of a liquid's resistance to flow, commonly checked with a flow cup and expressed in seconds. It determines atomisation quality and must be adjusted for gun type and temperature.

The breaking of liquid paint into a fine mist by air, pressure, or electrostatic force at the gun nozzle. Poor atomisation produces orange peel, dry spray, or mottled metallic finishes.

The nozzle opening that meters paint flow and, together with the needle, sets the spray pattern size. Tip size must suit the product, from fine clearcoat tips to larger primer tips.

The proportion of each spray pass that covers the previous one, typically around fifty percent. Consistent overlap gives even film build and avoids banding or stripes in metallic colours.

Technique of adjusting gun distance, speed, and a drop coat to orient aluminium flakes evenly so the finish looks uniform. Poor control causes mottling, striping, or a blotchy metallic appearance.

The transparent topcoat that provides gloss, UV protection, and chemical resistance over base colour. Its film build and cure determine durability and resistance to weathering.

The pigmented colour coat that provides hue and metallic effect beneath clearcoat. It is applied thin and even, since film thickness variations change the visible colour.

A surface texture resembling citrus skin caused by paint that does not flow out flat before setting. It results from wrong viscosity, gun settings, or insufficient flash and leveling time.

Small blisters or craters formed when trapped solvent escapes through a coating that has skinned over too quickly. It is prevented by correct flash times and appropriate thinner selection.

The waiting period between coats during which solvents evaporate before the next layer is applied. Too short a time traps solvent, while too long can harm intercoat adhesion.

A small particle of dust or lint trapped in a drying paint film, appearing as a raised speck. It is removed by sanding and polishing after the coating has fully cured.

A documented recipe of toners and amounts that reproduces a specific vehicle colour under a defined lighting condition. It may need tinting adjustments for variant colours and fading.

A factory colour that differs slightly between production plants or model years despite sharing one code. Painters compare spray-out cards to choose the closest variant before mixing.

A test card sprayed with the mixed colour and compared against the vehicle under correct lighting. It confirms the match before the full repair is painted.

The boundary where tape or paper stops paint from reaching adjacent panels or trim. A hard masking line must be positioned in a natural gap and removed before the film fully hardens.

The total dry thickness of coating applied, measured in micrometres with a gauge. Too little film gives poor durability, while too much can cause cracking or solvent entrapment.

An instrument, usually magnetic or ultrasonic, that measures coating thickness on a panel. Readings reveal prior repairs and help the estimator judge whether refinishing or replacement is needed.

The written authorisation listing operations, parts, materials, and agreed price for a repair. It protects both shop and customer and must be updated if additional damage is found.

The final step where the completed vehicle is inspected with the customer, care instructions are explained, and warranty terms are confirmed. It closes the repair order and documents acceptance.