NABTEB Light Vehicle Body Repair cheat sheet

Personal protective equipment for body repair: impact goggles plus face shield when grinding or cutting, hearing protection above 85 dB(A), nitrile gloves for solvents and epoxies, and respiratory protection matched to the hazard (P2/P3 particulate for dust, A1/A2 organic vapour cartridge for paints and thinners, supplied air for isocyanate clearcoats).

Isocyanate hardeners in 2K paints can cause occupational asthma; sensitisation is permanent, so any spray operation with 2K products requires air-fed breathing apparatus and skin coverage, not a dust mask.

Fuel and battery isolation precedes any welding, cutting or panel removal: disconnect the battery earth, remove or drain the fuel tank where practical, and never weld a tank that has contained fuel without inerting and documented purging.

Fire classes and extinguisher selection: Class A solids (water/foam), Class B flammable liquids (foam, dry powder, CO2), Class C gases, and electrical fires (CO2 or dry powder). Solvent stores and spray booths need Class B-rated extinguishers within reach.

Compressed air hazard: never use air to clean dust from skin or clothing; limit blow-gun pressure to 2 bar (30 psi) with a dead-man nozzle and eye protection, because air embolism and hearing damage occur at workshop line pressures.

Vehicle lifting: support on the manufacturer's jacking points, use axle stands rated above the vehicle mass, chock the wheels, and never work under a vehicle held only by a hydraulic jack or a two-post lift without locks engaged.

COSHH-style control hierarchy for refinish chemicals: eliminate, substitute (waterborne or high-solids), engineer controls (booth extraction, downdraught), then administrative controls, with PPE as the last barrier.

Grinding and cutting sparks travel several metres; keep solvent-soaked rags, thinners and paint containers out of the spark zone, and store oily rags in a self-closing metal bin to prevent spontaneous combustion.

High-voltage and SRS precautions: on hybrid/EV bodies, isolate the traction system per the manufacturer's procedure before structural work, and allow the specified delay before touching airbag modules or their wiring.

Panel hammer faces are classified by shape and crown: flat, pick/pointed, cross-peen, shrinking (crowned with a domed face) and planishing (flat, highly polished). Polished faces prevent stretching and marking of the panel surface.

Dollies: heel dolly for general off-dolly work, toe dolly for tight returns and flanges, curved dolly for wheel arches, and a slapping file or spoon for low-crown areas. The dolly is held firmly against the panel to act as a reaction mass.

Body files and vixen files: a body file (float) with a flexible blade reveals high and low spots by cutting only the highs; a vixen file has coarse curved teeth for rapid shaping of filler and lead.

Slide hammer and dent puller: a slide hammer with a self-tapping screw or weld-on stud delivers a pulling force along the panel normal; a stud welder with a copper gun and carbon-tipped tip is used for pulling without drilling.

Measuring systems: a dedicated bench/universal measuring system or a laser/computer measuring system compares control-point dimensions with the manufacturer's data sheet; tram gauges give only point-to-point comparison and cannot confirm datum alignment in three dimensions.

MIG/MAG set selection: 0.6 mm wire for thin sheet below 1 mm, 0.8 mm for 1–2 mm body panels, and 1.0 mm for structural sections; use CO2/argon mix for steel and reverse polarity with 100% argon for aluminium.

Spray gun anatomy and setup: fluid tip/needle/nozzle set (1.2–1.4 mm for basecoat, 1.4–1.8 mm for primer/filler), air cap for atomisation, fan adjustment, fluid knob and air regulator. Gun distance 150–200 mm, perpendicular to the surface.

Torque and clamping: use a calibrated torque wrench within its stated range (typically 20–100% of full scale), and never use a torque wrench to loosen fasteners.

Infrared and forced-air drying: IR short-wave lamps cure from the substrate outward and can overbake filler or warp thin panels; follow the product's temperature/time curve and measure panel temperature with a contact or IR thermometer.

Steel types in vehicle bodies: mild steel (easily formed, low strength), high-strength low-alloy (HSLA), and advanced high-strength steels (dual-phase, TRIP, boron/martensitic) used in occupant-cell structures; AHSS work-hardens and must not be heated above the manufacturer's limit.

Aluminium alloys: 5xxx (Al-Mg) for inner panels and 6xxx (Al-Mg-Si) for outer panels; 6xxx is heat-treatable and loses strength with excessive heat, so repair limits are stricter than for steel. Aluminium requires dedicated, segregated tools to avoid galvanic contamination.

Galvanic corrosion occurs when dissimilar metals (steel/aluminium, steel/stainless) are joined in the presence of an electrolyte; isolate with sealant, coated fasteners or a barrier layer.

Zinc-coated (galvanised/zincrometal) steel: the zinc sacrifices itself to protect the steel; grinding must remove only the coating at the weld zone, and the coating must be restored after repair with a zinc-rich primer.

Plastics used in body panels: PP/EPDM (bumpers, weldable with hot-air and rod), ABS, PC/ABS, PA (nylon, hygroscopic), PUR (flexible foam). Identification by ISO code moulded on the part or by a burn/solvent test.

Composite materials: SMC (sheet moulding compound) and GRP (glass-reinforced plastic) are thermosets that cannot be welded; repair by grinding back, bonding with epoxy or polyester resin and glass mat. Carbon fibre requires epoxy and cannot contact steel without isolation.

Thickness and strength: panel steel typically 0.6–1.2 mm; boron steel in B-pillars can exceed 1,500 MPa and is usually classified as not repairable - replacement only, per the manufacturer's body repair manual.

Sealers and adhesives: seam sealer (brushable or extruded, paintable), structural adhesive (two-part epoxy, high shear strength), and anti-flutter foam. Structural adhesive joints need a defined bond gap and cure time.

Paint system layers: pretreatment/ conversion coating, primer (anti-corrosion or etch), primer surfacer/filler, basecoat (colour), and clearcoat (UV and chemical protection). Waterborne basecoat requires controlled airflow and temperature for flash-off.

Thread standards: metric coarse and fine threads are designated by diameter × pitch (M8×1.25); thread pitch is the distance between crests. Unified threads (UNC/UNF) are specified by threads per inch. Never mix thread systems on a safety-critical joint.

Torque-to-yield (TTY) and stretch bolts deform plastically when tightened and must be replaced after use; they are tightened in stages to a torque plus a specified angle (e.g. 40 Nm + 90°).

Fastener grades: property class 8.8, 10.9 and 12.9 on metric bolts indicate tensile strength (8.8 ≈ 800 MPa); do not substitute a lower class in structural or suspension locations.

Body construction types: body-on-frame (ladder chassis, separate body), monocoque/unibody (stressed body shell with box sections), and spaceframe (aluminium extrusions and castings with bonded/riveted joints).

Rivets and rivet nuts: blind pop rivets for non-structural trim, structural blind rivets (e.g. monobolt) and self-piercing rivets for aluminium structures, rivet nuts/plusnuts for threaded inserts in thin sheet.

Clinching and hemming: clinch joints form a mechanical interlock without heat; hemming folds the outer panel edge over the inner panel, with adhesive applied in the hem for stiffness and corrosion protection.

Spot welds: resistance spot welding produces a weld nugget at the faying surface; weld pitch and nugget diameter are specified by the manufacturer (typical nugget 4–6 mm for 0.8 mm sheet). Removal by spot-weld drill or cutter leaves a hole that must be plug-welded or replaced.

Clips and trim fasteners: push-fit fir-tree clips, spring clips, scrivets and hook-and-loop. Single-use clips with deformed barbs should be replaced rather than reused.

Thread repair: helicoil/thread insert restores a damaged internal thread to the original size; a timesert provides a solid bushing. Oversize bolts are not an acceptable repair on structural joints.

Removal sequence: disconnect battery and isolate SRS, remove trim and seals, drill out spot welds with a spot-weld drill (pilot first, then full diameter), cut MIG-brazed or adhesive joints, and support the panel before the last joint is released.

Spot-weld drill technique: centre-punch the weld, use a pilot drill of 3 mm, then a spot-weld cutter of 8 mm; do not drill through both layers, and remove residual nugget with a belt sander.

Panel alignment sequence: align the largest fixed panel first (usually the rear quarter or the door aperture), then fit the door to the aperture, then the front wing to the door and bonnet, adjusting gaps at hinges, shims and slotted mountings.

Gap and flush specification: typical door gaps are 4–6 mm with flushness within ±1 mm; measure with a gap gauge or plasticine impression and record before strip-down as a baseline.

Hinge adjustment: fore/aft by loosening hinge-to-body bolts, up/down by hinge-to-door bolts, and in/out by shims or slotted holes. Adjust with the door closed and the latch engaged where the design allows.

Bonded panels: heated release (induction or heat gun to the adhesive's softening point), cut the adhesive bead with a wire or blade, and do not lever the panel because it distorts. New adhesive requires a defined bead profile, primer and clamp time.

Structural section replacement: cut only at the manufacturer's designated sectioning points, use a butt joint with a backing insert or an overlap as specified, and preserve the original corrosion protection and weld count.

Glass and trim removal before panels: remove the windscreen or quarter glass where the aperture overlaps the repair, and label and store clips and fasteners by location for refitting.

Post-repair checks: check panel gaps, latch operation, water test, electrical function and headlamp aim after any front-end structural work; record measurements against the manufacturer's control-point data.

Direct (on-dolly) method: the panel is struck against a dolly held behind the damage; it stretches the metal and is used to raise a low area or to planish a stretched crown.

Indirect (off-dolly) method: the dolly is held beside the hammer blow, so the panel is pushed back into shape without thinning; it is the primary method for removing shallow dents.

Hammer selection: a pick/pointed hammer concentrates force for starting a low spot, a flat hammer for planishing, and a shrinking hammer (serrated or crowned face) for drawing metal together.

Reading the panel: a body file or a guide coat reveals high and low areas. High spots are marked and tapped down; low spots are raised from the back or pulled.

Stretching occurs when the metal is worked beyond its elastic limit; it shows as an oil-can or drum effect and cannot be corrected by hammering alone - it needs shrinking.

Panel beating sequence: rough out the damage from the back, then planish, then file and check, then shrink the stretched areas, then finish with a fine file or sander before filling.

Dolly contact: hold the dolly firmly against the panel with the hand behind, keeping the dolly face parallel to the panel; a loose dolly bounces and produces a hammer mark on the outside.

Heat shrinking is a last resort on modern high-strength panels; the manufacturer's repair manual may prohibit heat above a stated temperature (often 200 °C for AHSS, lower for some boron steels).

Aluminium panel beating: use dedicated hammers and dollies, work with light blows, and anneal only where the alloy permits (6xxx can be annealed and re-aged; 5xxx work-hardens and cannot be heat-treated).

Shrinking reduces surface area to remove a stretched, oil-canned area; stretching increases surface area to fill a low area or to form a crown. Both change the metal's thickness and must be followed by planishing.

Heat shrinking: heat a spot to a dull red (approximately 600–700 °C on mild steel) with an oxy-acetylene torch and a neutral flame, then quench with a damp cloth or water while the metal is still hot; the rapid contraction of the heated spot shrinks the area.

Torch shrinking without quenching: heat a spot, then hammer the surrounding metal toward the hot spot while it cools; the hot spot contracts on cooling and draws the surrounding metal with it.

Shrinking hammer and dolly: a shrinking hammer has a serrated or crowned face that gathers metal; it is used with a dolly or a slapping spoon. Excessive use thins and work-hardens the panel.

Stretching by hammer and dolly: hammer off-dolly around the low area to stretch the metal into the depression; this is a controlled operation and is followed by planishing to smooth the surface.

Heat-shrinking sequence: identify the stretched area, heat a small spot (10–20 mm), quench, check with a file or straight edge, and repeat in small steps; overheating a large area causes warping and loss of strength.

Heat limits: never heat boron or martensitic steels; most manufacturers prohibit heat on AHSS above about 200 °C, and some prohibit heat entirely. Check the repair manual before any torch work.

Aluminium shrinking: heat to the point where a pine stick or soap marks the surface (about 200–250 °C), then quench; do not overheat, because 6xxx alloys lose strength and may crack.

Metal finishing after shrinking: planish the area, file the surface, and check for high spots; a stretched area that still drums after shrinking indicates the shrink was insufficient or the metal is over-worked.

MIG/MAG welding (GMAW): DC electrode positive for steel with CO2/argon mix; wire feed speed sets current, voltage sets arc length. Typical body sheet settings: 0.8 mm wire, 60–90 A, 15–18 V, gas flow 10–15 L/min.

MIG brazing (CuSi3 wire): lower heat input than steel welding, used on high-strength and zinc-coated steels to avoid zinc burn-off and heat damage. The joint is a brazed fillet, not a fusion weld, and must not be confused with a structural weld.

Resistance spot welding (RSW): current passes through the electrodes and the faying surface; parameters are current, time and electrode force. Weld nugget diameter is checked by a peel test or chisel test on a sample.

TIG (GTAW): AC for aluminium with a pure tungsten or zirconiated electrode, DCEN for steel with a thoriated or lanthanated electrode; used for thin sheet and visible joints. Filler rod is added separately.

Oxy-acetylene welding and brazing: a neutral flame is used for steel; a carburising flame for brazing. Brazing temperature is above 450 °C but below the melting point of the parent metal; the filler flows by capillary action.

Adhesive bonding: structural two-part epoxy or polyurethane; surface preparation (abrasion, cleaning, primer) is critical. Bond gap is controlled by glass beads or a carrier mesh, and clamp time follows the product data sheet.

Weld defects: porosity (gas or contamination), lack of fusion (low current or fast travel), burn-through (excess current or thin sheet), spatter (wrong gas or wire), and undercut (excess current or wrong angle).

Distortion control: use a stitch or back-step sequence, clamp or jig the panel, allow cooling between runs, and use a copper backing bar to draw heat away on thin sheet.

Post-weld protection: remove slag and spatter, treat with zinc-rich primer, and apply seam sealer and cavity wax to restore corrosion protection. Never leave bare welds on a structural repair.

Body filler types: polyester filler (standard, for filling dents), fibreglass-reinforced filler (for bridging holes and rust repairs), metal-filled filler (for high-build and heat resistance), and glazing putty (for pinholes and fine scratches).

Surface preparation: bare metal must be abraded to P80–P120, cleaned with a wax and grease remover, and primed or etched before filler. Filler must not be applied over paint, rust, or silicone contamination.

Mixing: measure the hardener (typically 2% by weight for a benzoyl peroxide paste) and mix thoroughly to a uniform colour. Too much hardener causes cracking and shrinkage; too little causes a tacky, uncured surface.

Application: spread with a flexible plastic spreader in thin coats, pressing firmly to exclude air, and build in layers rather than one thick coat. Maximum thickness is usually 3–5 mm; thicker areas should be repaired with panel replacement or fibreglass.

Sandings: shape with P80–P120, refine with P180–P240, and finish with P320–P400 before primer. Use a sanding block, not fingers, to keep the surface flat.

Feather edging: taper the filler edge into the surrounding paint or primer so the repair is invisible; the edge should be a smooth transition, not a step.

Pinholes and porosity: caused by air trapped during mixing or spreading, or by solvent entrapment. Fill with glazing putty or a high-build primer after the filler has cured.

Curing: polyester filler cures by an exothermic reaction; cure time is shortened by warmth and lengthened by cold. Do not sand until fully cured, and do not apply filler over damp or cold metal.

Safety: filler hardener is an organic peroxide and is corrosive and flammable; wear nitrile gloves and eye protection, and store away from heat and organic materials.

Surface preparation sequence: wash, degrease with wax and grease remover, abrade (P80–P180 for bare metal, P320–P400 for paint), clean again, then apply the correct primer for the substrate.

Primer types: etch primer (for bare steel and aluminium, provides adhesion and corrosion protection), epoxy primer (for bare metal and as a sealer), and primer surfacer/filler (for filling sanding scratches and levelling).

Sanding: use a dual-action or orbital sander with the correct grit progression, a sanding block for flat areas, and a guide coat (a light dusting of contrasting colour) to reveal low spots and scratches.

Feather edging and blending: sand the repair edge until it is smooth and invisible; blend the new paint into the adjacent panel within a natural break line.

Masking: use masking tape and paper or plastic sheeting; mask apertures, trim and glass, and use a soft-edge masking tape for blend panels. Never mask over wet paint.

Tack rags remove dust before painting; use them lightly and change them often. A tack rag that is too dry or contaminated can leave residue.

Primer application: etch primer in thin coats (do not sand), epoxy primer as a sealer, and primer surfacer in 2–3 coats, then sand with P400–P600 before basecoat.

Panel wipe and static: use an anti-static or de-ionising blow-off and a tack rag; static attracts dust and causes fisheyes.

Final inspection: check for sanding scratches, pinholes, and contamination under a bright light before topcoat; any defect visible in primer will show through the topcoat.

Spray gun setup: fluid tip 1.2–1.4 mm for basecoat and clearcoat, 1.4–1.8 mm for primer; air pressure at the gun 2–3 bar (30–45 psi) for HVLP; fan width about 200–250 mm at 150–200 mm distance.

Spray technique: hold the gun perpendicular to the surface, move at a constant speed, overlap each pass by 50%, and trigger before and after the panel edge. Distance 150–200 mm for HVLP.

Basecoat application: apply 2–3 coats with flash-off between coats (typically 5–15 minutes at 20 °C), building to full hiding. Waterborne basecoat needs airflow and controlled humidity.

Clearcoat application: apply 2 coats, with a flash-off of 5–10 minutes, then allow the full cure. Clearcoat thickness is typically 40–60 µm; too thin gives poor UV protection, too thick causes runs and solvent pop.

Common defects: runs (too much material or too close), orange peel (too little air pressure or too fast thinner), fisheyes (silicone contamination), solvent pop (too much material or too short flash-off), and dust (poor booth cleanliness).

Spray booth: downdraught booth with filtered air, positive pressure and extraction; temperature 20–25 °C and relative humidity 50–60% for most refinish products.

Gun cleaning: flush with thinner, clean the air cap and fluid tip with a brush, and never soak the whole gun in thinner. Lubricate the needle packing and check the air cap for damage.

Flash-off and drying: follow the product data sheet for flash-off times and force-dry or IR cure schedules; overbaking causes loss of gloss and adhesion failure.

Personal protection: air-fed respirator for 2K products, nitrile gloves, and coveralls; solvent vapour is heavier than air and accumulates at floor level, so extraction must be at low level.

Colour codes: the vehicle's paint code is on the identification plate or sticker (often in the engine bay, door jamb or under the bonnet); it identifies the original colour, but variants exist within the same code.

Variant chips: manufacturers supply variant chips or a spectrophotometer reading to match the actual colour on the vehicle, because fading, repair history and plant differences cause variation.

Three-stage and tri-coat colours: a ground coat, a mid-coat (pearl or tint) and a clearcoat; matching requires the correct number of mid-coats and a spray-out card to check the colour.

Metallic and pearl control: metallic flake orientation depends on gun distance, pressure, and a drop coat (a light, dust coat) to orient the flakes; too dry a coat gives a lighter, rougher finish.

Blending: apply the colour to the repair area and blend into the adjacent panel within a natural break; use a blender or a reduced basecoat to fade the edge.

Spray-out card: spray a test card with the mixed colour, allow it to dry, and compare it with the vehicle in natural daylight, not under artificial light.

Tinting: adjust the mixed colour with small additions of tinting colours (toners); record the additions so the formula can be repeated.

Clearcoat over blend: apply clearcoat over the blended area and the whole panel where possible; a blend within the clearcoat requires a blender or a soft-edge technique.

Colour matching under light: use a colour-corrected light booth or natural daylight; metallic colours change with viewing angle (flop), so check at 45° and 90°.

Windscreen bonding: original glass is bonded with a polyurethane adhesive to a primed aperture; the adhesive needs a minimum bead profile (typically 8–12 mm wide by 6–10 mm high) and a defined drive-away time.

Primer system: glass primer and body primer are applied to the frit and the aperture, then the adhesive is applied. The frit (black ceramic band) protects the adhesive from UV.

Glass removal: use a wire or blade to cut the adhesive, protect the paint with tape, and use suction cups to handle the glass. Do not lever the glass against the aperture.

Seals and weatherstrips: push-fit or clipped seals; replace deformed or torn seals, and apply a silicone or rubber lubricant to aid fitting. Seals must not be painted.

Trim clips: fir-tree, spring and scrivet clips are single-use where the barbs deform; replace rather than reuse. Use a trim removal tool to avoid damaging the panel.

ADAS and glazing: cameras and sensors mounted behind the windscreen require recalibration after glass replacement; the vehicle must be on a level surface with correct tyre pressures and a full fuel tank or specified load.

Water test: after glazing or seal replacement, carry out a water test with a hose at low pressure, checking for leaks at the aperture and around the seals.

Accessories: roof rails, spoilers and mirrors are mounted with clips, bolts or adhesive; follow the torque and adhesive cure times, and check the electrical connections for mirrors and cameras.

Heated rear screens: the heating element is a printed grid on the glass; repair with a conductive paint only where the manufacturer allows, and check continuity with a multimeter.

Damage classification: direct damage (at the impact point), indirect damage (transferred through the structure), and inertia damage (caused by the mass of components continuing to move).

Measuring systems: a universal bench or a laser/computer measuring system compares control points with the manufacturer's data sheet; tram gauges give only point-to-point comparison and cannot confirm three-dimensional alignment.

Control points and datum: the datum is a horizontal reference plane; control points are specified holes and features on the underbody. Measurements are taken to the centre line and to the datum.

Frame straightening: pull in the direction opposite to the impact, in stages, with the vehicle anchored; use a pulling tower or a bench system and monitor measurements during the pull. Overpulling causes new damage.

Structural inspection: check for kinks, cracks, torn metal, failed spot welds, and deformation of the occupant cell. Any deformation of the crumple zone or the safety cell is a replacement or sectioning decision.

Sectioning: cut only at the manufacturer's designated sectioning points, use the specified joint type (butt with backing insert or overlap), and restore the original weld count and corrosion protection.

Suspension and steering: check for bent struts, wishbones and steering arms after a side or front impact; measure the wheel alignment and check the subframe mounting points.

Hybrid and EV structural work: isolate the high-voltage system before any structural repair, and do not heat or cut near the battery pack or orange high-voltage cables.

Documentation: record before and after measurements, photograph the damage, and keep the repair method and parts used for the vehicle's history and any warranty or insurance claim.