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AMPP Bridge Coatings practice questions

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Question 1Surface Preparation and Substrate Condition

Which surface preparation standard defines near-white blast cleaning?

  1. SSPC-SP 7 / NACE No. 4
  2. SSPC-SP 6 / NACE No. 3
  3. SSPC-SP 10 / NACE No. 2 Correct answer.
  4. SSPC-SP 5 / NACE No. 1

Explanation

Near-white blast cleaning is defined by SSPC-SP 10 / NACE No. 2. It permits faint shadows, streaks, or discoloration but no visible oil, grease, dirt, mill scale, rust, coating, or other residue. White metal is SSPC-SP 5 / NACE No. 1, and commercial is SSPC-SP 6 / NACE No. 3.

Question 2Surface Preparation and Substrate Condition

A specification requires commercial blast cleaning. Which standard applies?

  1. SSPC-SP 7 / NACE No. 4
  2. SSPC-SP 5 / NACE No. 1
  3. SSPC-SP 6 / NACE No. 3 Correct answer.
  4. SSPC-SP 10 / NACE No. 2

Explanation

Commercial blast cleaning is SSPC-SP 6 / NACE No. 3. It requires removal of all visible oil, grease, dirt, mill scale, rust, and coating, while allowing stains and shadows. SSPC-SP 10 is near-white and SSPC-SP 5 is white metal.

Question 3Surface Preparation and Substrate Condition

Mill scale on new steel consists mainly of which iron oxide?

  1. Iron sulfide (FeS)
  2. Magnetite (Fe3O4) Correct answer.
  3. Iron carbonate (FeCO3)
  4. Iron chloride (FeCl2)

Explanation

Mill scale is a layered oxide formed at high temperature, and magnetite (Fe3O4) is a major constituent. It is tightly adherent, brittle, and cathodic to steel, so incomplete removal can accelerate localized corrosion. Hematite and wustite may also be present.

Question 4Surface Preparation and Substrate Condition

What minimum temperature difference above the dew point is commonly required before abrasive blasting or coating?

  1. 1°C (2°F)
  2. 2°C (3°F)
  3. 3°C (5°F) Correct answer.
  4. 0°C (0°F)

Explanation

A common rule is that the steel temperature must be at least 3°C (5°F) above the dew point before blasting or coating. This margin reduces condensation risk as conditions change. A smaller margin, or any surface below dew point, leaves moisture that harms adhesion.

Question 5Surface Preparation and Substrate Condition

Which tool is used to measure abrasive blast profile by pressing a tape onto the surface?

  1. Wet film gauge
  2. Pull-off tester
  3. Replica tape Correct answer.
  4. Bresle patch

Explanation

Replica tape is pressed against the blast profile and its compressed thickness is measured with a gauge. The resulting value indicates the anchor profile depth. Bresle patches measure salts, wet film gauges measure coating thickness, and pull-off testers measure adhesion.

Question 6Surface Preparation and Substrate Condition

Which field method extracts soluble salts from a steel surface using a flexible patch and distilled water?

  1. Blotter test
  2. Tape adhesion test
  3. Kesternich test
  4. Bresle patch Correct answer.

Explanation

The Bresle patch method, described in ISO 8502-6, injects distilled water into a patch sealed to the steel, extracts dissolved salts, and analyzes the solution. It is a field method for soluble salt contamination. Blotter tests check compressed air cleanliness, not surface salts.

Question 7Surface Preparation and Substrate Condition

What nozzle angle to the surface generally gives the most efficient abrasive cleaning?

  1. 45 to 60 degrees
  2. 30 to 45 degrees
  3. 10 to 20 degrees
  4. 75 to 90 degrees Correct answer.

Explanation

A nozzle angle near 75 to 90 degrees to the surface transfers the most energy into cleaning and profile formation. Shallow angles deflect abrasive and reduce efficiency. The exact angle may be adjusted for access, but near-perpendicular is standard.

Question 8Surface Preparation and Substrate Condition

Why must oil and grease be removed before abrasive blasting?

  1. They reduce the consumption of abrasive
  2. They increase the anchor profile significantly
  3. They contaminate steel and abrasive Correct answer.
  4. They accelerate the removal of rust

Explanation

Oil and grease interfere with abrasive contact and can be spread by the blast stream. They also remain on the steel and cause coating adhesion failures. Precleaning with solvent or detergent is required before blasting.

Question 9Surface Preparation and Substrate Condition

SSPC-SP 5 / NACE No. 1 requires what final appearance?

  1. At least 70% bare metal
  2. Only loose rust removed
  3. Faint shadows and streaks allowed
  4. Uniform gray-white, no residue Correct answer.

Explanation

SSPC-SP 5 / NACE No. 1 is white metal blast cleaning. The finished surface is uniformly gray-white and free of visible oil, grease, dirt, mill scale, rust, coating, oxides, and other residue. Faint shadows are not permitted under this grade.

Question 10Surface Preparation and Substrate Condition

ISO 8501-1 rust grade D describes steel with what condition?

  1. Uniform light rust without pitting
  2. Pitting and general corrosion Correct answer.
  3. Tightly adherent mill scale
  4. Slight rusting on mill scale

Explanation

ISO 8501-1 grade D represents steel that has rusted enough to cause pitting. The surface shows general corrosion and pits, with mill scale largely gone. Grades A through C describe progressively more rusting with less pitting.

Question 11Surface Preparation and Substrate Condition

Why are chloride salts on a blast-cleaned surface harmful?

  1. They act as a bonding primer
  2. They improve coating adhesion
  3. They cause osmotic blistering Correct answer.
  4. They increase the surface profile

Explanation

Chlorides and other soluble salts are hygroscopic and create osmotic cells under a coating. Water passes through the film, salts draw it inward, and blistering or disbondment results. Even invisible salt films can shorten coating life.

Question 12Surface Preparation and Substrate Condition

What is a typical abrasive blasting standoff distance from nozzle to surface?

  1. 4 to 6 inches
  2. 30 to 36 inches
  3. 1 to 3 inches
  4. 12 to 24 inches Correct answer.

Explanation

A typical standoff is about 12 to 24 inches (300 to 600 mm). Too close concentrates energy and can overheat or damage the surface; too far wastes abrasive and reduces cleaning. The best distance depends on nozzle size and pressure.

Question 13Surface Preparation and Substrate Condition

Compared with fine abrasive, coarse abrasive generally produces what result?

  1. A deeper anchor profile Correct answer.
  2. A smoother surface
  3. A shallower profile
  4. No profile

Explanation

Coarser abrasive particles cut deeper and produce a rougher, deeper anchor profile. Finer abrasive produces a shallower profile and is often used where a smooth finish is needed. Profile depth must match the coating specification.

Question 14Surface Preparation and Substrate Condition

Why should weld spatter be removed before coating?

  1. It creates coating voids at peaks Correct answer.
  2. It prevents rust from forming
  3. It lowers the steel temperature
  4. It improves the coating gloss

Explanation

Weld spatter creates sharp, irregular projections that can hold blast debris and leave thin or voided coating at the peaks. It should be ground smooth before blasting and coating. Coating over spatter can also produce holidays and premature corrosion.

Question 15Surface Preparation and Substrate Condition

What is the purpose of grinding sharp edges before coating?

  1. To increase the steel thickness greatly
  2. To give uniform coating coverage Correct answer.
  3. To remove all mill scale from steel
  4. To create a deep anchor profile

Explanation

Sharp edges and corners are difficult to coat uniformly because surface tension pulls liquid coating away from the edge. Grinding a small radius improves coverage and reduces thin spots. This is a common requirement in bridge coating specifications.

Question 16Surface Preparation and Substrate Condition

Deep pitting on a steel surface is significant because of what risk?

  1. It raises the dew point of the air
  2. Coating can bridge pits, leaving voids Correct answer.
  3. It improves the coating adhesion greatly
  4. It eliminates salts from the steel

Explanation

Deep pits can retain salts, moisture, and abrasive debris after blasting. A coating may bridge over a pit and leave a void or pinhole that becomes a corrosion initiation site. Pitting should be assessed and may require more aggressive preparation.

Question 17Surface Preparation and Substrate Condition

Which standard covers waterjetting to a defined surface cleanliness?

  1. SSPC-SP 3
  2. SSPC-SP 6 / NACE No. 3
  3. SSPC-SP 12 / NACE No. 5 Correct answer.
  4. SSPC-SP 2

Explanation

SSPC-SP 12 / NACE No. 5 defines waterjetting to surface cleanliness levels. It uses pressurized water, sometimes with abrasives, to remove coating and contaminants without the profile produced by dry abrasive blasting. SSPC-SP 6 and SP 3 are abrasive and power tool standards.

Question 18Surface Preparation and Substrate Condition

Which SSPC standard covers power tool cleaning?

  1. SSPC-SP 5
  2. SSPC-SP 1
  3. SSPC-SP 10
  4. SSPC-SP 3 Correct answer.

Explanation

SSPC-SP 3 covers power tool cleaning, using tools such as grinders, wire brushes, and sanders. SSPC-SP 1 is solvent cleaning, SP 5 is white metal blast, and SP 10 is near-white blast. Power tool cleaning is suitable where blasting is not practical.

Question 19Surface Preparation and Substrate Condition

Rust bloom appearing shortly after blast cleaning most likely indicates what condition?

  1. Excess abrasive grit
  2. An overly high profile
  3. Proper surface preparation
  4. Salt or moisture Correct answer.

Explanation

Rust bloom is fresh, visible corrosion that forms soon after blasting. It usually indicates moisture, high humidity, condensation, or residual salt on the steel. The surface should be re-evaluated and cleaned before coating if bloom is present.

Question 20Surface Preparation and Substrate Condition

Which test checks compressed air for oil and water contamination?

  1. Pull-off test
  2. Bresle test
  3. Replica tape
  4. Blotter test Correct answer.

Explanation

The blotter test, described in ASTM D4285, directs compressed air onto a clean white blotter. Oil or water droplets collected on the paper indicate contaminated air. Clean, dry compressed air is needed for blasting and spraying.

Question 21Surface Preparation and Substrate Condition

A soluble salt test reports conductivity. What does this indicate?

  1. Coating thickness
  2. Surface roughness
  3. Anchor profile depth
  4. Ionic contamination level Correct answer.

Explanation

A soluble salt test measures conductivity, which reflects the concentration of dissolved ions in the extraction solution. The result is converted to an equivalent chloride concentration or reported as conductivity. It does not measure profile, coating thickness, or roughness.

Question 22Surface Preparation and Substrate Condition

If blast profile is much deeper than the coating specification allows, what risk arises?

  1. The salt level on the steel drops
  2. Coating bridges peaks, leaving voids Correct answer.
  3. The steel surface becomes too smooth
  4. The coating will cure much too fast

Explanation

Excessively deep profile creates sharp peaks that a thin coating may not cover. The coating can bridge between peaks and leave voids at the valleys, allowing corrosion to start. Profile must be within the range specified for the coating system.

Question 23Surface Preparation and Substrate Condition

What is appropriate abrasive blast preparation for hot-dip galvanized steel before coating?

  1. Sweep blast with non-metallic grit Correct answer.
  2. An acid wash followed by rinsing
  3. A white metal blast with coarse grit
  4. No surface preparation is needed

Explanation

Galvanized steel should be prepared by sweep blasting with a non-metallic abrasive to create a light profile and remove zinc reaction products without removing the zinc layer. White metal blasting can remove the protective zinc coating. Acid washing alone is not a coating preparation method.

Question 24Surface Preparation and Substrate Condition

When overcoating an aged coating system, secondary surface preparation should include what action?

  1. Remove loose coating and feather edges Correct answer.
  2. Leave all rust spots intact
  3. Apply primer directly over chalk
  4. Blast through to bare steel everywhere

Explanation

Secondary preparation of an aged coating system should remove loose, chalked, or contaminated coating and feather the edges of intact coating. This provides a sound base and smooth transition for the new coat. Coating over chalk or rust spots can lead to early failure.

Question 25Surface Preparation and Substrate Condition

Recycled abrasive should be tested for what property?

  1. Contamination and particle size Correct answer.
  2. Color, odor, and appearance
  3. Wet coating thickness on steel
  4. Electrical conductivity of the grit

Explanation

Recycled abrasive can accumulate dust, coating fragments, salts, and fines, and its particle size distribution can change. Testing helps confirm that it remains clean and within the specified grade. Color and odor are not adequate quality checks.

Question 26Surface Preparation and Substrate Condition

Before abrasive blasting or coating, the steel surface temperature should be at least how far above the dew point?

  1. 3 °C (5 °F) Correct answer.
  2. At the dew point
  3. 10 °C (18 °F)
  4. 1 °C (2 °F)

Explanation

Industry practice and most coating specifications require the steel temperature to be at least 3 °C (5 °F) above the dew point before blasting or painting. This margin keeps condensation from forming as ambient conditions fluctuate. Condensation would contaminate the prepared surface and cause adhesion loss.

Question 27Surface Preparation and Substrate Condition

What is the commonly specified maximum relative humidity for conventional dry abrasive blasting?

  1. 50%
  2. 100%
  3. 85% Correct answer.
  4. 95%

Explanation

Dry abrasive blasting is commonly limited to a maximum relative humidity of about 85%. Above that level, moisture condensation on the steel and in the blast air becomes likely. Lower limits may be imposed for moisture-sensitive coatings, but 85% is the usual general ceiling.

Question 28Surface Preparation and Substrate Condition

Which field method measures abrasive blast profile by pressing a compressible tape against the surface and measuring its thickness?

  1. Replica tape pressed against the profile Correct answer.
  2. Pull-off testing of coating adhesion
  3. Wet film measurement with a comb gauge
  4. Tape lift testing for surface dust

Explanation

Replica tape is a compressible foam tape pressed against the blast profile and then measured with a spring micrometer. Subtracting the tape's base thickness from the measured value gives the profile depth. Comparator discs and stylus instruments are alternatives, but replica tape is the common field technique.

Question 29Surface Preparation and Substrate Condition

Why must mill scale be removed from steel before coating?

  1. It is cathodic and drives attack at breaks. Correct answer.
  2. It is softer than steel and wears away rapidly.
  3. It blocks the abrasive from cutting the steel.
  4. It traps chlorides that cannot be removed.

Explanation

Mill scale is a dense iron oxide layer that is cathodic to the underlying steel. At breaks or edges, the small exposed steel area becomes anodic and corrodes rapidly, undercutting the scale and the coating. Mill scale must therefore be removed to expose clean steel.

Question 30Surface Preparation and Substrate Condition

What is the function of the anchor pattern produced by abrasive blasting?

  1. It provides a mechanical key for coating adhesion. Correct answer.
  2. It removes soluble salts from the surface.
  3. It indicates the steel's alloy composition.
  4. It seals the steel against moisture.

Explanation

Abrasive blasting produces a roughened profile, often called the anchor pattern, which gives the coating a mechanical key and increases the bonded surface area. The profile depth must fall within the coating manufacturer's specified range. Too shallow a profile weakens adhesion, while excessive profile can leave thin peaks.

Question 31Surface Preparation and Substrate Condition

Which SSPC surface preparation standard covers solvent cleaning to remove oil, grease, and soil?

  1. SSPC-SP 6
  2. SSPC-SP 2
  3. SSPC-SP 3
  4. SSPC-SP 1 Correct answer.

Explanation

SSPC-SP 1, Solvent Cleaning, covers removal of oil, grease, dirt, soil, salts, and contaminants by solvent, vapor, alkaline, emulsion, or steam cleaning. It is normally the first step before any mechanical surface preparation. Removing grease first prevents it from being smeared into the surface during blasting or wire brushing.

Question 32Surface Preparation and Substrate Condition

Which SSPC standard describes hand tool cleaning?

  1. SSPC-SP 10
  2. SSPC-SP 3
  3. SSPC-SP 1
  4. SSPC-SP 2 Correct answer.

Explanation

SSPC-SP 2 covers hand tool cleaning with wire brushes, scrapers, chisels, and sandpaper. It removes loose mill scale, rust, and paint but does not produce a blast profile. Power tool cleaning is covered by SSPC-SP 3.

Question 33Surface Preparation and Substrate Condition

Which SSPC abrasive standard specifies requirements for new ferrous metallic abrasives?

  1. SSPC-AB 2
  2. SSPC-AB 1
  3. SSPC-PA 2
  4. SSPC-AB 3 Correct answer.

Explanation

SSPC-AB 3 sets requirements for new ferrous metallic abrasives. Recycled ferrous metallic abrasive is addressed by SSPC-AB 2, while SSPC-AB 1 covers mineral and slag abrasives. Using the correct grade helps control cleanliness and profile.

Question 34Surface Preparation and Substrate Condition

Why should weld undercut be ground before coating?

  1. It traps abrasive that cannot be blown off.
  2. It creates a sharp crevice coatings cannot fill. Correct answer.
  3. It raises steel hardness above the coating limit.
  4. It alters the alloy so the coating will not cure.

Explanation

Undercut at a weld toe is a sharp, narrow groove that a coating may bridge rather than fill. The resulting void or thin film can become a starting point for corrosion and coating breakdown. Grinding the toe to a smooth transition lets the coating form a continuous film.

Question 35Surface Preparation and Substrate Condition

A lamination at the edge of a steel plate is exposed during surface preparation. Why is this a concern?

  1. It shows the steel plate has absorbed moisture.
  2. It makes the steel too hard for the abrasive to cut.
  3. It always lowers the blast profile below specification.
  4. It may open into a crevice that coating cannot seal. Correct answer.

Explanation

A lamination is a flattened internal discontinuity in the steel. If it reaches an edge and opens, it forms a tight crevice that blasting and coating cannot properly clean or seal, allowing moisture to enter and corrosion to progress. Such defects should be evaluated and may require repair before coating.

Question 36Surface Preparation and Substrate Condition

What problem can occur when steel is very hot during application of a solvent-borne coating?

  1. The coating cures too slowly and sags.
  2. The steel absorbs solvent and swells.
  3. Solvent flashes off too fast, causing dry spray. Correct answer.
  4. The coating becomes too hard to measure.

Explanation

On a hot surface, solvent in the coating evaporates very rapidly, so the film may not flow out and level. This produces dry spray, poor coalescence, and pinholes that reduce barrier protection. Applicators may need to cool the steel or adjust the coating to suit the conditions.

Question 37Surface Preparation and Substrate Condition

What is the main risk of using abrasive that has absorbed moisture?

  1. The abrasive attracts oil from the steel.
  2. It clogs equipment and promotes flash rust. Correct answer.
  3. The profile depth increases uncontrollably.
  4. The abrasive becomes too round to cut.

Explanation

Moisture in abrasive causes feeding and clogging problems in the blast pot and hose, and it carries water to the freshly blasted steel. The result can be flash rust and contamination before the coating is applied. Abrasive should be stored dry and checked before use.

Question 38Surface Preparation and Substrate Condition

What is the purpose of a corrosion inhibitor in wet abrasive blasting?

  1. To limit flash rust on cleaned steel Correct answer.
  2. To increase the cutting speed of the abrasive
  3. To thicken the slurry for better coverage
  4. To neutralize abrasive dust in the air

Explanation

Wet abrasive blasting uses water to control dust, which makes the freshly cleaned steel prone to flash rust. A corrosion inhibitor is added to the water to delay rusting until the coating can be applied. The inhibitor does not replace proper surface preparation or drying.

Question 39Surface Preparation and Substrate Condition

How does SSPC-SP 10 near-white blasting compare with SSPC-SP 5 and SSPC-SP 6?

  1. It is less thorough than SP 5 and more thorough than SP 6. Correct answer.
  2. It is identical to SP 6 except for allowed salts.
  3. It is identical to SP 5 except for allowed moisture.
  4. It is more thorough than SP 5 and less thorough than SP 6.

Explanation

SSPC-SP 10 (NACE No. 2) allows faint shadows, streaks, or discoloration on a small percentage of the surface. It is less thorough than SSPC-SP 5 white metal, which permits no staining, and more thorough than SSPC-SP 6 commercial blast. The specified degree must match the coating's requirements.

Question 40Surface Preparation and Substrate Condition

Why can crushed slag abrasive leave a surface unsuitable for coating?

  1. It reacts chemically with steel to form a brittle layer.
  2. It leaves an oily film that repels the coating.
  3. Fragments can embed and later cause coating defects. Correct answer.
  4. It polishes the surface so no profile forms.

Explanation

Some abrasives, especially certain slags, can fracture during impact and embed fine fragments in the steel surface. These inclusions can interfere with adhesion and create defects, so the abrasive must be clean and compatible and the surface inspected. Contaminated abrasive can also deposit salts or dust that must be removed.

Question 41Coating Materials, Selection, and Specification

In a three-coat bridge coating system, what is the primary function of the zinc-rich primer?

  1. Provide the finished color and gloss of the system
  2. Provide galvanic protection to the steel substrate Correct answer.
  3. Absorb ultraviolet radiation before it reaches the intermediate coat
  4. Eliminate the need for surface preparation of the steel

Explanation

Zinc dust in the primer is anodic to steel, so it corrodes preferentially and protects exposed steel at scratches and damaged areas. Color, gloss, and ultraviolet resistance come from the topcoat, and no primer removes the need for proper surface preparation.

Question 42Coating Materials, Selection, and Specification

A self-curing inorganic zinc silicate primer applied in a fabrication shop develops its cure mainly by reacting with what?

  1. A catalyst injected at the spray gun
  2. Ultraviolet light from sunlight
  3. Moisture in the air Correct answer.
  4. Oxygen in the air

Explanation

Inorganic zinc silicates hydrolyze and condense using atmospheric moisture, which is why very low humidity or cold conditions retard cure. Shop areas are therefore often humidified or the coating is given extra time before topcoating.

Question 43Coating Materials, Selection, and Specification

In a typical three-coat bridge system, what is the main function of the epoxy intermediate coat?

  1. Provide sacrificial galvanic protection to the steel
  2. Provide resistance to ultraviolet degradation at the surface
  3. Supply the exterior color and gloss
  4. Build barrier film thickness and tie the primer to the topcoat Correct answer.

Explanation

The intermediate coat adds barrier thickness, hides primer porosity, and provides a sound substrate for the finish coat. Galvanic protection belongs to the zinc primer and weathering resistance belongs to the topcoat.

Question 44Coating Materials, Selection, and Specification

Which topcoat is normally specified where long-term color and gloss retention in sunlight are important?

  1. Coal tar epoxy
  2. Zinc-rich primer
  3. Aromatic polyurethane
  4. Aliphatic polyurethane Correct answer.

Explanation

Aliphatic polyurethane binders resist ultraviolet breakdown, so they hold color and gloss far better than aromatic types. Aromatic polyurethanes chalk and yellow, and epoxies are generally too UV-sensitive for exterior finish service.

Question 45Coating Materials, Selection, and Specification

What is the purpose of a stripe coat on a bridge?

  1. To reduce the surface profile before the next coat is applied
  2. To build extra film on edges, welds, and corners that are hard to coat uniformly Correct answer.
  3. To mark the boundaries between adjacent coating layers
  4. To create a slip-resistant walking surface on the deck

Explanation

Spray application produces thinner films at edges and irregular geometry, so a brush or roller stripe coat is applied to build the required thickness there. This reduces early rusting at the locations most prone to coating breakdown.

Question 46Coating Materials, Selection, and Specification

Micaceous iron oxide is added to an epoxy intermediate coat mainly to do what?

  1. Provide galvanic protection to the steel
  2. Accelerate the cure of the epoxy
  3. Create a lamellar barrier that lengthens the diffusion path for water and oxygen Correct answer.
  4. Reduce the abrasion resistance of the film

Explanation

Micaceous iron oxide particles are plate-like and align parallel to the substrate, which slows penetration of water, oxygen, and ions through the film. It does not contribute galvanic action or speed curing.

Question 47Coating Materials, Selection, and Specification

Which surface preparation standard is normally specified before applying a zinc silicate primer to bridge steel?

  1. SSPC-SP 1 solvent cleaning only
  2. SSPC-SP 10 near-white blast cleaning Correct answer.
  3. SSPC-SP 3 power tool cleaning
  4. SSPC-SP 2 hand tool cleaning

Explanation

Inorganic and organic zinc-rich primers need a clean, profiled, essentially salt-free surface, normally near-white blast cleaning to SSPC-SP 10. Solvent, hand, and power tool cleaning leave mill scale and rust that prevent galvanic contact and adhesion.

Question 48Coating Materials, Selection, and Specification

SSPC-PA 2 is the standard that governs which of the following?

  1. Gloss retention rating of a topcoat
  2. Soluble salt limits before painting
  3. The number and location of dry film thickness measurements Correct answer.
  4. The degree of abrasive blast cleaning

Explanation

SSPC-PA 2 sets out how many thickness readings to take, where to take them, and how to judge conformance with a specified dry film thickness. It does not address salt limits, blast cleanliness, or appearance ratings.

Question 49Coating Materials, Selection, and Specification

What is the principal limitation of an aromatic polyurethane used as an exterior topcoat?

  1. It has poor resistance to abrasion and impact
  2. It cures only at temperatures above 30 degrees Celsius
  3. It cannot be applied over an epoxy intermediate coat
  4. It chalks and yellows under ultraviolet exposure Correct answer.

Explanation

Aromatic polyurethane chemistry absorbs ultraviolet light and degrades, producing chalking and yellowing, so it is normally reserved for interior or non-exposed work. Aliphatic polyurethanes were developed to overcome this weakness.

Question 50Coating Materials, Selection, and Specification

A two-component epoxy intermediate coat has been left far beyond its recoat window and has developed amine blush. What is the correct action before topcoating?

  1. Apply the topcoat immediately to seal the surface
  2. Wash the surface to remove the blush, allow it to dry, and abrade to restore adhesion Correct answer.
  3. Add extra curing agent to the topcoat to overcome the blush
  4. Wipe with solvent and apply the topcoat while the surface is still wet

Explanation

Amine blush is a surface deposit of amine carbonate that blocks adhesion, so it must be removed by washing before the film is abraded and topcoated. Applying a coat over blush traps the contamination and causes intercoat delamination.