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ITI Mechanic Auto Body Painting (AITT Theory) study materials
ITI Mechanic Auto Body Painting (AITT Theory) study resources

ITI Mechanic Auto Body Painting (AITT Theory) practice questions

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Question 1Trade Safety, Tools, and Workshop Practice

In an auto body spray booth, which class of fire extinguisher is the primary choice for a solvent or paint fire?

  1. Class D sodium chloride extinguisher
  2. Class A water extinguisher
  3. Class B foam or dry chemical extinguisher Correct answer.
  4. Class C carbon dioxide extinguisher only

Explanation

Solvents, thinners and paint liquids are flammable liquids, which fall into Class B. A Class B-rated dry chemical or foam extinguisher smothers the fire and is the standard first-response choice near a spray booth. Water is dangerous on solvent fires because it can spread the burning liquid.

Question 2Trade Safety, Tools, and Workshop Practice

Before entering a spray booth to paint, the painter must wear a supplied-air respirator. Why is an air-purifying respirator with organic vapour cartridges insufficient for isocyanate paints?

  1. Cartridges are only rated for dust and cannot filter any vapour.
  2. Supplied air is required only for comfort and offers no health protection.
  3. Cartridges are too heavy to wear inside a booth for long periods.
  4. Isocyanates can pass through or break through cartridges and are not reliably removed. Correct answer.

Explanation

Isocyanate vapours and aerosols are poorly removed by organic vapour cartridges and breakthrough can occur without warning. Supplied-air or airline respirators provide clean breathing air independent of the contaminant concentration. This is why isocyanate paints require supplied air rather than cartridge respirators.

Question 3Trade Safety, Tools, and Workshop Practice

A painter needs to check whether a two-pack primer has been mixed at the correct ratio. Which workshop tool or practice gives the most reliable result?

  1. Estimating by eye in the mixing cup
  2. Adding extra hardener until the colour looks right
  3. Weighing each component on a paint mixing scale Correct answer.
  4. Judging by the smell of the mixture

Explanation

Two-pack products must be mixed at the manufacturer's stated ratio, and weighing on a dedicated mixing scale is the reliable way to achieve it. Eyeballing or adding extra hardener changes the ratio and can cause curing faults. The scale removes guesswork and is standard practice.

Question 4Trade Safety, Tools, and Workshop Practice

Which statement best describes the correct use of a paint mixing scale in the body shop?

  1. It measures the temperature of the booth.
  2. It measures the volume of each component in millilitres.
  3. It measures the weight of each component so the ratio is set by mass. Correct answer.
  4. It measures the viscosity of the mixed paint.

Explanation

A mixing scale works by mass, so each component is added until the displayed weight matches the required ratio. This is more accurate than volume for paints with different densities. Viscosity and temperature are measured with different instruments.

Question 5Trade Safety, Tools, and Workshop Practice

A gravity-feed spray gun is being set up for a basecoat. Which adjustment controls the amount of paint that flows through the fluid needle when the trigger is fully pulled?

  1. The fluid control Correct answer.
  2. The air inlet regulator on the gun
  3. The fan (pattern) control
  4. The trigger stop screw

Explanation

The fluid control knob limits how far the fluid needle opens, and therefore how much paint flows at full trigger. The fan control shapes the spray pattern, while the regulator sets inlet air pressure. The trigger stop screw is not the standard fluid-setting device on most guns.

Question 6Trade Safety, Tools, and Workshop Practice

A painter notices the spray pattern from a gravity gun is split into two separate streams with a dry centre. Which cause is most likely?

  1. Air pressure set too high
  2. Fluid control set too far open
  3. Paint viscosity too low
  4. Blocked or partially blocked fluid nozzle or air cap holes Correct answer.

Explanation

A split or dry-centred pattern usually means the fluid nozzle or air cap holes are partially blocked or dirty. Cleaning the nozzle and air cap restores an even pattern. Too much fluid or too much air would give a different fault, such as runs or excessive overspray.

Question 7Trade Safety, Tools, and Workshop Practice

What is the main reason for using a downdraft spray booth rather than an open workshop area for refinishing?

  1. It keeps the paint warm so it cures faster.
  2. It draws air downward and filters it, removing overspray and protecting the painter and finish. Correct answer.
  3. It allows the painter to work without a respirator.
  4. It increases the flash-off time of the paint.

Explanation

A downdraft booth moves filtered air from ceiling to floor, carrying overspray and solvent vapour away from the painter and the wet panel. This protects both the operator and the quality of the finish. It does not replace respirator use.

Question 8Trade Safety, Tools, and Workshop Practice

A technician is about to use an angle grinder with a cutting disc to remove a damaged panel section. Which practice is correct?

  1. Remove the guard so the disc fits into the tight space.
  2. Keep the guard fitted, wear eye and face protection, and check the disc is rated for the tool speed. Correct answer.
  3. Use a worn disc that is smaller than the rated size to reduce kickback.
  4. Run the grinder without the side handle for better control.

Explanation

The guard must stay fitted, the disc must be rated for the grinder's maximum speed, and eye and face protection are essential. These measures contain fragments and reduce injury if the disc fails. Removing guards or handles defeats the tool's designed safety features.

Question 9Trade Safety, Tools, and Workshop Practice

When using a two-pack isocyanate paint, which combination of controls is required in addition to a supplied-air respirator?

  1. Only safety glasses, since the paint is applied in a booth.
  2. Skin and eye protection, adequate ventilation, and booth extraction. Correct answer.
  3. Only a dust mask and cotton gloves.
  4. No extra controls, because the respirator handles all exposure routes.

Explanation

Isocyanates can affect the skin and eyes as well as the lungs, so gloves, coveralls, eye protection and effective extraction are needed alongside the respirator. A respirator alone does not control skin or eye contact. A dust mask and cotton gloves give no protection against isocyanate paint.

Question 10Trade Safety, Tools, and Workshop Practice

Which solvent is commonly used for cleaning spray guns and flushing lines, and why must it be handled in a well-ventilated area?

  1. Brake fluid, because it dissolves paint quickly.
  2. Gun-wash solvent such as a lacquer thinner, because it is flammable and gives off harmful vapours. Correct answer.
  3. Engine oil, because it lubricates the gun.
  4. Water, because it is non-flammable and harmless.

Explanation

Lacquer thinner and similar gun-wash solvents dissolve paint residues but are flammable and emit harmful vapours. They must be used in a ventilated area away from ignition sources. Water cannot dissolve most solvent-based paints, and brake fluid or engine oil are not cleaning solvents.

Question 11Trade Safety, Tools, and Workshop Practice

After cleaning a spray gun, what is the correct way to store it to avoid damage and contamination?

  1. Leave it soaking in solvent indefinitely.
  2. Store it with paint left in the cup to keep the seals wet.
  3. Store it with the fluid needle fully tightened against the nozzle.
  4. Trigger it dry several times, wipe it, and store it clean with the air cap protected. Correct answer.

Explanation

A gun should be cleaned, dried by triggering, wiped, and stored with the air cap protected. Leaving it in solvent or with paint inside can damage seals and clog passages. Tightening the needle hard against the nozzle can damage the seat.

Question 12Trade Safety, Tools, and Workshop Practice

A can of mixed two-pack clearcoat is left in the workshop and begins to heat up and swell. What is the safest immediate action?

  1. Move it away from ignition sources to a safe, ventilated area and let it cool, following the safety data sheet. Correct answer.
  2. Add more thinner to slow the reaction.
  3. Seal it tightly and place it in a closed cabinet.
  4. Open the lid to release pressure and keep working.

Explanation

A two-pack mix that heats and swells is reacting exothermically, and the container can rupture. It should be moved away from ignition sources to a safe, ventilated area and allowed to cool, in line with the safety data sheet. Sealing it or adding thinner can worsen the hazard.

Question 13Trade Safety, Tools, and Workshop Practice

Which item of personal protective equipment is most important when sanding cured primer with a dual-action sander?

  1. A dust mask or respirator rated for fine dust, plus eye protection. Correct answer.
  2. A welding helmet.
  3. A rubber apron only.
  4. Ear defenders only.

Explanation

Sandng primer creates fine dust, so a dust-rated respirator and eye protection are the key controls. A welding helmet is not appropriate, and an apron or ear defenders alone do not protect the lungs or eyes. Dust extraction on the sander also helps.

Question 14Trade Safety, Tools, and Workshop Practice

A technician is asked to prepare a bare steel panel for body filler. Which step sequence is most appropriate?

  1. Clean and degrease, remove rust and old coatings to bare metal, abrade the surface, then apply filler. Correct answer.
  2. Apply filler directly over the rust, then sand smooth.
  3. Apply a thick coat of wax and grease remover and fill over it.
  4. Sand the panel with water and apply filler while it is still wet.

Explanation

Filler needs a clean, abraded, rust-free metal surface to bond properly. Degreasing and removing rust and old coatings first prevents contamination and poor adhesion. Applying filler over rust, wax or water leads to failure.

Question 15Trade Safety, Tools, and Workshop Practice

Why must a technician avoid using compressed air from a general workshop line to blow dust off their clothing before painting?

  1. It uses too much electricity.
  2. It removes the static charge needed for adhesion.
  3. It can drive dust and solvent into the skin and eyes and spread contamination onto the panel. Correct answer.
  4. Compressed air is too cold to be useful.

Explanation

Blowing clothing with compressed air can force particles and solvent into the skin and eyes, and it spreads dust onto freshly prepared surfaces. Proper dust removal uses extraction or a tack cloth. Compressed air is not a safe cleaning method for the body.

Question 16Trade Safety, Tools, and Workshop Practice

A spray gun's air cap has two small horns with holes. What is the function of these horn holes?

  1. They supply fluid to the nozzle.
  2. They hold the fluid needle in place.
  3. They act as a drain for excess solvent.
  4. They direct air to shape and atomise the spray pattern. Correct answer.

Explanation

The horn holes on the air cap direct air streams that shape and atomise the pattern. Fluid is supplied through the fluid nozzle, not the horns. Correct horn hole condition is essential for an even fan.

Question 17Trade Safety, Tools, and Workshop Practice

A workshop stores thinners and paints in a metal cabinet. Which practice best meets fire-safety expectations?

  1. Keep flammable liquids in a labelled, closed flammable-liquids cabinet away from ignition sources, with spill containment. Correct answer.
  2. Store all containers together regardless of type, with the cabinet door open for ventilation.
  3. Store thinners next to the spray booth heater to keep them warm.
  4. Store containers on the floor in walkways for easy access.

Explanation

Flammable liquids belong in a labelled, closed flammable-liquids cabinet away from ignition sources, with spill containment. This limits vapour release and fire spread. Storing them near heaters or in walkways creates ignition and obstruction hazards.

Question 18Trade Safety, Tools, and Workshop Practice

A painter reports dizziness and headache while spraying in a booth. What is the most appropriate immediate response?

  1. Turn up the gun pressure to finish faster.
  2. Stop work, leave the area to fresh air, and report the exposure so ventilation and PPE can be checked. Correct answer.
  3. Drink water and continue in the booth.
  4. Continue painting and open a window later.

Explanation

Dizziness and headache can indicate solvent overexposure, so work should stop and the person moved to fresh air, with the exposure reported. Ventilation, respirator fit and booth function should then be checked. Continuing work increases exposure and risk.

Question 19Trade Safety, Tools, and Workshop Practice

Which statement about the safe handling of a high-pressure airless spray unit is correct?

  1. The unit must be depressurised and the tip removed before cleaning or servicing the gun. Correct answer.
  2. Skin injection injuries from airless units are harmless if washed immediately.
  3. The gun can be pointed at people as long as the trigger is not pulled.
  4. The tip guard can be removed when spraying in tight areas.

Explanation

Airless units hold very high pressure, so the system must be depressurised and the tip removed before servicing. Injection injuries are serious and require immediate medical attention. The tip guard must stay fitted and the gun must never be pointed at people.

Question 20Trade Safety, Tools, and Workshop Practice

A technician is choosing abrasive grit for sanding. Which pairing of grit number to purpose is correct?

  1. Coarse grit such as 80 for final finishing before topcoat.
  2. Coarse grit such as 80 for removing paint and shaping filler. Correct answer.
  3. Fine grit such as 400 for stripping heavy paint.
  4. Fine grit such as 400 for shaping body filler.

Explanation

Lower grit numbers are coarser and are used for stripping paint and shaping filler. Higher grit numbers are finer and are used for finishing and featheredging. Matching grit to the task prevents unnecessary removal of material or poor finish.

Question 21Surface Preparation and Substrate Assessment

When inspecting a steel panel before refinishing, which condition must be removed completely because it will cause poor adhesion and blistering if painted over?

  1. Light surface dust
  2. Faint sanding scratches from 320 grit
  3. A thin film of wax and grease remover
  4. Mill scale and rust Correct answer.

Explanation

Mill scale is a hard oxide layer formed during steel rolling, and rust is iron oxide; both are loosely bonded and prevent the paint film from gripping the substrate. If left beneath primer they trap moisture and cause lifting, blistering and premature failure. They must be removed by abrasive blasting, grinding or chemical treatment before any primer is applied.

Question 22Surface Preparation and Substrate Assessment

A technician is preparing a bare aluminium panel. Which surface treatment is required before applying primer to ensure adhesion and corrosion resistance?

  1. Sand with 80 grit and paint immediately
  2. Apply a conversion coating or etch primer designed for aluminium Correct answer.
  3. Wipe with silicone remover only
  4. Apply a heavy coat of body filler directly

Explanation

Aluminium oxidises instantly in air, forming a passive oxide layer that paint will not bond to reliably. A conversion coating or an etch primer containing phosphoric acid conditions the surface and provides a stable key for subsequent primer. Mechanical sanding alone does not prevent the oxide from reforming before the primer cures.

Question 23Surface Preparation and Substrate Assessment

Why must a plastic bumper be identified for its substrate type before refinishing?

  1. Because all plastics require the same primer and topcoat
  2. Because different plastics need different adhesion promoters and flexible additives Correct answer.
  3. Because plastic panels cannot be painted
  4. Because plastic never needs cleaning

Explanation

Plastics vary widely in surface energy and flexibility; polypropylene and TPO need a specialised adhesion promoter, while rigid thermosets may only need scuffing. Using the wrong primer leads to peeling or cracking when the flexible part deflects. Identification symbols moulded into the part guide the correct preparation route.

Question 24Surface Preparation and Substrate Assessment

Which defect is indicated by a solvent-popped, pinhole appearance in a freshly applied primer surfacer over a repaired area?

  1. Dry spray
  2. Solvent trapping in body filler Correct answer.
  3. Orange peel
  4. Sagging

Explanation

Solvent popping occurs when solvent trapped in porous body filler or under a skin-formed primer escapes through the drying film, leaving pinholes. It signals that the filler was not fully cured or that flash-off times were too short between coats. Proper drying and thinner coats prevent the defect.

Question 25Surface Preparation and Substrate Assessment

What is the purpose of a guide coat when block sanding a repaired panel?

  1. To add build thickness to the primer
  2. To reveal low spots and imperfections as the sanding progresses Correct answer.
  3. To seal the panel against moisture
  4. To speed up the curing of body filler

Explanation

A guide coat is a thin contrasting mist applied over primer; as the technician block sands, the guide coat remains in low areas and disappears from high spots. This shows where filler or primer still needs levelling. It is a diagnostic aid, not a build or sealing layer.

Question 26Surface Preparation and Substrate Assessment

A panel has been stripped to bare steel and shows a slight oil can dent. Which preparation step is most appropriate before applying filler?

  1. Apply wax and grease remover and topcoat
  2. Paint directly over the dent
  3. Feather the area, clean it, and apply filler after removing the paint edge Correct answer.
  4. Apply filler over the dent without treatment

Explanation

The dent must be feathered to a smooth edge and the bare steel cleaned of contamination so the filler can bond mechanically and chemically. Filler should never bridge a sharp paint edge, which causes a visible ring and adhesion failure. Cleaning removes oils that would prevent the filler from curing properly.

Question 27Surface Preparation and Substrate Assessment

Which abrasive grade is typically used to featheredge existing paint before applying primer surfacer?

  1. 24 grit
  2. 1500 grit
  3. 80 to 180 grit Correct answer.
  4. 600 grit

Explanation

Featheredging requires an abrasive coarse enough to cut the paint edge down smoothly but not so coarse that it leaves deep scratches. Grades around 80 to 180 grit achieve a tapered edge that primer can fill. Finer grades polish rather than cut, and coarser grades gouge the panel.

Question 28Surface Preparation and Substrate Assessment

A technician notices a shiny, glossy ring around a repaired area after primer surfacer is applied. What is the most likely cause?

  1. The featheredge was not sanded finely enough to remove gloss Correct answer.
  2. The panel was too cold
  3. The spray gun was held too close
  4. The primer was mixed too thin

Explanation

A glossy halo indicates the original topcoat edge was not abraded back far enough, so the primer cannot key to the slick surface. The edge must be feathered with progressively finer grit until the gloss is gone. Proper featheredging eliminates the ring and prevents peeling.

Question 29Surface Preparation and Substrate Assessment

What does a substrate identification symbol such as 'PP' moulded into a bumper indicate to the refinisher?

  1. That the part is polypropylene and requires a special adhesion promoter Correct answer.
  2. That the part is steel and must be primed with etch primer
  3. That the part is fibreglass and must be gel-coated
  4. That the part is polyurethane and needs no preparation

Explanation

Moulded ISO symbols identify the plastic so the technician can select the correct preparation and coating system. PP (polypropylene) has very low surface energy and needs a dedicated adhesion promoter before primer. Treating it like a rigid plastic leads to peeling.

Question 30Surface Preparation and Substrate Assessment

Which condition on a galvanised steel panel must be addressed before painting?

  1. The panel must be painted without any preparation
  2. The panel must be heated to red heat
  3. The zinc coating must be completely removed to bare steel
  4. The surface must be cleaned and treated with a suitable primer for zinc Correct answer.

Explanation

Galvanised steel carries a zinc coating that can react with some primers and cause adhesion loss or blistering. The surface should be cleaned, degreased and coated with a primer formulated for zinc, often after a light abrade or etch. Removing all zinc defeats the corrosion protection the coating provides.

Question 31Surface Preparation and Substrate Assessment

A technician is assessing a panel that has been repaired previously. Which sign most strongly suggests the old repair used excessive body filler?

  1. A slight texture under the paint
  2. A magnetic gauge reading much thicker than surrounding metal Correct answer.
  3. A uniform colour match
  4. A smooth, flat surface

Explanation

An electronic or magnetic thickness gauge reveals the total film build over the steel; a reading far above the surrounding panel indicates a thick filler layer. Excessive filler is prone to cracking and should be investigated before recoating. Texture, colour and flatness alone do not quantify filler depth.

Question 32Surface Preparation and Substrate Assessment

What is the main risk of painting over a panel that still has traces of silicone contamination?

  1. Improved adhesion
  2. Brighter colour development
  3. Faster drying of the topcoat
  4. Fish eyes and cratering in the paint film Correct answer.

Explanation

Silicone lowers the surface tension of the paint, causing it to draw away from contaminated spots and form fish eyes or craters. The defect appears as circular voids in the finish and is difficult to repair once cured. Thorough cleaning with a dedicated silicone remover is essential.

Question 33Surface Preparation and Substrate Assessment

Which method is best for detecting low spots on a bare metal panel before body filler work?

  1. Running a hand or a straight edge across the surface and observing reflections Correct answer.
  2. Tapping with a hammer
  3. Visual inspection under normal room light
  4. Measuring the panel temperature

Explanation

Low spots are hard to see under diffuse light, so technicians use a straight edge, hand feel, or a reflection line to reveal depressions. A bright light held at a low angle also shows the contour. These methods locate the exact depth and position for filler application.

Question 34Surface Preparation and Substrate Assessment

Which substrate requires the use of a non-conductive or isolated preparation method because of spark risk during sanding?

  1. Steel
  2. Aluminium
  3. Glass-reinforced plastic
  4. Carbon fibre composite Correct answer.

Explanation

Carbon fibre is electrically conductive, and sanding dust can create a conductive path or spark hazard near electrical equipment. Technicians use isolated tools and control dust carefully. Steel and aluminium are metals but are handled with normal metal preparation precautions, while GRP is non-conductive.

Question 35Surface Preparation and Substrate Assessment

What is the correct order of operations when preparing a bare steel panel for refinishing?

  1. Clean, remove rust and scale, sand, prime Correct answer.
  2. Prime, clean, sand, topcoat
  3. Topcoat, prime, clean, sand
  4. Sand, topcoat, clean, prime

Explanation

Preparation always starts with cleaning to remove contamination, followed by removal of rust and mill scale, then sanding to create a key, and finally priming. Reversing the order drives contamination into the surface or traps rust under the coating. Each step builds on the previous one.

Question 36Surface Preparation and Substrate Assessment

A technician finds a patch of paint that lifts when solvent is wiped over it. What does this most likely indicate?

  1. The paint is fully cured and solvent-resistant
  2. The solvent is the wrong brand
  3. The panel is too clean
  4. The existing finish is a lacquer or uncured coating that is not solvent-resistant Correct answer.

Explanation

A solvent wipe that lifts or softens the existing finish shows the coating is not resistant to the refinish solvents, often because it is an old lacquer or an improperly cured film. Such areas must be stripped or sealed with an isolating sealer. Painting over them causes wrinkling and lifting.

Question 37Surface Preparation and Substrate Assessment

Which type of primer is most appropriate over a bare metal surface to provide corrosion protection and adhesion?

  1. Clear lacquer
  2. Flexible bumper primer
  3. Water-based topcoat
  4. Epoxy or etch primer Correct answer.

Explanation

Epoxy primers provide excellent corrosion protection and adhesion on bare metal, while etch primers chemically bond to the metal surface. Topcoats and clear lacquers lack the corrosion inhibitors needed directly on metal. Flexible bumper primers are formulated for plastic, not bare steel.

Question 38Surface Preparation and Substrate Assessment

Why should a panel be wiped with a tack cloth immediately before topcoat application?

  1. To soften the primer
  2. To speed up solvent evaporation
  3. To remove dust and lint that would cause surface defects Correct answer.
  4. To add a static charge to the panel

Explanation

Tack cloths pick up fine dust and lint that ordinary wiping can leave behind. These particles cause nibs, dirt inclusions and roughness in the topcoat. A light tack wipe just before spraying keeps the surface clean without leaving residue.

Question 39Surface Preparation and Substrate Assessment

A repaired area shows a faint outline of the filler edge after topcoat. Which preparation fault is most likely?

  1. The topcoat was applied too thin
  2. The filler edge was not feathered smoothly into the surrounding paint Correct answer.
  3. The panel was cleaned with wax and grease remover
  4. The filler was feathered too widely

Explanation

A visible outline, sometimes called a halo or ring, appears when the filler or primer edge is left as a step rather than tapered. The topcoat highlights the transition. Proper featheredging with progressively finer abrasives blends the repair into the panel.

Question 40Surface Preparation and Substrate Assessment

What does a magnetic thickness gauge measure when assessing a steel panel?

  1. The hardness of the steel
  2. The colour depth of the topcoat
  3. The total thickness of non-magnetic coatings over the steel Correct answer.
  4. The temperature of the panel

Explanation

A magnetic gauge measures the distance between its probe and the ferrous substrate, which corresponds to the total film build of paint, primer and filler. This helps identify excessive build or previous repairs. It does not measure colour, temperature or hardness.

Question 41Surface Preparation and Substrate Assessment

Which factor most affects the choice between a direct-to-metal primer and a primer surfacer on a repaired panel?

  1. The need for corrosion protection versus the need to fill sanding scratches Correct answer.
  2. The brand of spray gun
  3. The ambient humidity only
  4. The colour of the topcoat

Explanation

Direct-to-metal primers are formulated for adhesion and corrosion protection on bare metal, while primer surfacers are designed to build and fill minor imperfections. The repair condition determines which function is needed, and often both are used in sequence. Topcoat colour, gun brand and humidity alone do not dictate the primer type.

Question 42Surface Preparation and Substrate Assessment

What is the purpose of scuffing a previously painted panel with a fine abrasive before applying a new topcoat?

  1. To soften the old paint
  2. To create a mechanical key for adhesion of the new coating Correct answer.
  3. To increase the gloss of the old finish
  4. To remove the old colour completely

Explanation

Scuffing creates microscopic scratches that increase surface area and allow the new coating to grip mechanically. It does not need to remove the old colour. The surface is then cleaned before the new topcoat is applied.

Question 43Surface Preparation and Substrate Assessment

A technician is preparing a fibreglass panel with visible air voids and exposed fibres. Which step is essential before priming?

  1. Sand with 1500 grit only
  2. Fill the voids and seal the surface to prevent solvent penetration Correct answer.
  3. Wipe with water and paint immediately
  4. Apply topcoat directly over the fibres

Explanation

Exposed fibres and voids in fibreglass can absorb solvents and cause swelling, pinholes or adhesion failure. The surface must be filled and sealed, often with a suitable primer or gelcoat-compatible product, before topcoat. Sanding alone does not close the porosity.

Question 44Surface Preparation and Substrate Assessment

Which practice best prevents cross-contamination when preparing different substrates in the same workshop?

  1. Dedicating tools and abrasives to metal, plastic and composite work Correct answer.
  2. Storing primers in open containers
  3. Using the same sanding disc for all materials
  4. Cleaning tools only at the end of the week

Explanation

Dedicated tools and abrasives prevent particles from one substrate, such as steel grit or plastic dust, from embedding in another and causing defects. Cross-contamination can cause rust spots in paint or poor adhesion on plastic. Regular cleaning and sealed containers also support good workshop practice.

Question 45Paint Materials, Mixing, and Color Matching

When mixing a two-component primer surfacer, what does the mixing ratio on the product data sheet refer to?

  1. The ratio of base component to hardener by volume or weight Correct answer.
  2. The ratio of primer to topcoat for a blended repair
  3. The ratio of primer to thinner needed for spraying viscosity
  4. The ratio of reducer to additive for flow control

Explanation

The mixing ratio states how much base component must be combined with a given amount of hardener, expressed by volume or by weight as the manufacturer specifies. Thinner is added afterward to reach spray viscosity and is not part of that ratio. Using the wrong ratio disrupts the cure chemistry and can leave a soft or brittle film.

Question 46Paint Materials, Mixing, and Color Matching

A technician measures basecoat components by weight instead of by volume. Which property of the components makes this acceptable only when the data sheet permits it?

  1. Each component has the same flash point
  2. Each component has the same viscosity
  3. Each component has a different density Correct answer.
  4. Each component has a different colour

Explanation

Volume and weight ratios only agree when the densities of the components are equal, and resin, hardener and thinner densities usually differ. That is why a manufacturer publishes separate volume and weight ratios. Mixing by weight using a volume ratio silently shifts the stoichiometry and can upset cure.

Question 47Paint Materials, Mixing, and Color Matching

Why must a manufacturer's recommended induction time be observed after mixing a two-component product?

  1. To let pigment settle for a uniform colour
  2. To let solvent evaporate to the target viscosity
  3. To allow the chemical reaction to begin before application Correct answer.
  4. To allow air bubbles to rise out of the mixture

Explanation

Induction time lets the crosslinking reaction start so the product behaves as designed during spraying and flow-out. Skipping it can change flow, levelling and adhesion. Settling, solvent loss and bubble release are side effects of standing, not the reason the data sheet specifies the interval.

Question 48Paint Materials, Mixing, and Color Matching

A mixed two-component clearcoat has passed its pot life. What is the correct action?

  1. Strain it and continue spraying
  2. Discard it and mix a fresh batch Correct answer.
  3. Add a small amount of fresh hardener and continue
  4. Add extra reducer to extend its use

Explanation

Once the pot life has elapsed the mixture has reacted too far to cure correctly, so it must be discarded. Adding reducer or hardener cannot restore the intended stoichiometry and risks poor adhesion, gloss loss or failure. Straining removes skins but does not restore usable chemistry.

Question 49Paint Materials, Mixing, and Color Matching

Which factor most strongly shortens the pot life of a mixed two-component product in the spray booth?

  1. Brighter booth lighting
  2. Lower relative humidity
  3. Higher ambient temperature Correct answer.
  4. Higher booth air velocity

Explanation

Chemical reaction rates rise with temperature, so a warm booth shortens pot life noticeably. Air velocity affects solvent flash-off at the surface rather than the bulk reaction. Lighting and lower humidity have comparatively little effect on the cure reaction in the pot.

Question 50Paint Materials, Mixing, and Color Matching

What is the main purpose of a viscosity cup when preparing paint for spraying?

  1. To check that the reduced paint flows within the specified time Correct answer.
  2. To confirm the hardener has fully reacted
  3. To measure the thickness of the cured paint film
  4. To measure the pigment concentration of the paint

Explanation

A viscosity cup measures the time for a fixed volume of paint to drain through a calibrated orifice, which indicates whether the mixture is within the sprayable range. Film thickness is checked with a gauge after curing. Cup time says nothing about reaction completeness or pigment loading.