Causes of Paint Film Defects

Defective paint films are usually the result of either improper preparation of the paint or substrate surface, or lack of control of processing variables. Paint film defects attributable to improper baking procedures are listed in Table 7; other paint film defects and frequent causes are listed in Table 9.

Table 9 Common causes of paint film defects

Defect

Cause

Susceptible application methods

Poor adhesion (peeling, flaking, poor bonding)

Paint applied over grease, oil, water, alkali residues, or other foreign materials on surface

Dip, flow, roller, spray

Finish coat applied over incompletely dried undercoat

Dip, flow, roller, spray

Paint applied to surface that is too hot (above 71 °C, or 160 °F) or too cold (below 16 °C, or 60 °F) or too cold (below 16 °C, or 60 °F)

Dip, flow, spray

Film too thick

Dip, flow, roller, spray

Beading

Solvent vaporizes too rapidly

Dip, flow

Parts drawn from paint too rapidly

Dip

Blistering (pimpling, bubbling, pinholing, pitting)

Moisture entrapped on surface of substrate

Dip, flow, roller, spray

Air entrapment

Improper solvents

Dip, flow, roller,

spray

Wide temperature differential between paint and work

Dip, flow, roller, spray

Insufficient drying time between coats; solvent trapped in undercoat escapes through partially dried finish coat

Dip, flow, roller, spray

Excessive air pressure and dry spraying of undercoat, causing porosity and air pockets under finish coat

Spray

Water in air line

Spray

Excess paint film, entrapping solvents

Brittleness

Improper composition of paint

Dip, flow, roller, spray

Checking (alligatoring, crazing, crowfooting, hairlining)

Application of finish coat over incompletely dried undercoat

Dip, flow, roller, spray

Insufficient mixing of material to blend all pigment

Dip, flow, roller, spray

Color separation

Incomplete mixing of paint before application

Dip, flow, roller, spray

Poor agitation during application

Dip, roller, spray

Cracking (shrinking, splitting)

Paint not thoroughly mixed before application

Dip, flow, roller, spray

Surface not completely clean

Dip, flow, roller, spray

Insufficient thinner

Dip, flow, roller, spray

Undercoat too thick

Dip, flow, roller, spray

Surfaces too hot or too cold

Dip, flow, spray

Oil or water in air line

Spray

Cratering

Surface air bubbles

Silicone contamination

Dip, flow, spray

Slow drying

Application over grease, oil, or fingerprints

Dip, flow, roller, spray

Application of too much paint

Dip, flow, roller, spray

Poor ventilation, air drying only

Dip, flow, roller, spray

Drying atmosphere too cold or too humid, air drying only

Dip, flow, roller, spray

Oil in air line

Spray

Solvent vaporizes too slowly

Dip, flow, roller, spray

Dusty or gritty appearance (dry spray)

Insufficient solvent

Spray

Solvent vaporizes too rapidly

Spray

Excessive air pressure

Spray

Spray gun too far (over 305 mm, or 12 in.) from work

Spray

Excess air movement in spray booth

Spray

Spray pattern too wide,

Airborne particles reach substrate

Edge pull-away

Solvent vaporizes too slowly

Dip, flow

Too much solvent

Dip, flow

Poor flow-out

Viscosity of paint too high

Dip, flow, roller, spray

Temperature of paint too low

Dip, flow, roller

Solvent vaporizes too rapidly

Dip, flow, roller,

spray

Temperature of surface too low

Spray

Poor gloss

Paint film too thin

Dip, flow, roller, spray

Application over incompletely dried undercoat

Dip, flow, roller, spray

Drying atmosphere too cold or too humid, air drying only

Drip, flow, roller, spray

Application over alkali residues

Dip, flow, roller, spray

Too much solvent vapor in drying oven

Dip, flow, roller, spray

Improper solvent

Too much heat in cure cycle

Roller

Poor hiding

Pigment settling because of poor agitation

Dip, flow, roller, spray

Solvent vaporizes too slowly

Dip, flow

Too much solvent

Dip, flow, roller

Withdrawal from paint too slow

Dip

Vapor concentration too high

Dip, flow

Nonuniform film thickness (or uncoated areas)

Solvent vaporizes too slowly

Dip, flow

Nonuniform roll pressure; roll out-of-round

Roller

Improper hanging of panels

Dip, flow

Paints not lapping properly when spraying

Orange peel

Excessive film thickness

Dip, flow, roller, spray

Surface temperature too hot or too cold

Flow, dip, spray

Improper adjustment of spray gun pattern

Spray

Air pressure too high

Spray

Solvent vaporizes too rapidly

Dip, flow, roller, spray

Improper applicator/metering roll speeds

Roller

Undesirable pattern

Swelling of roll

Roller

Roll improperly ground

Roller

Foreign material on roll

Roller

Poor spray gun technique

Spray

Runs (curtains, sags)

Too much solvent

Dip, flow, spray

Paint surface or drying atmosphere too hot or too cold

Dip, flow, spray

Solvent vaporizes too slowly

Dip, flow, spray

Excessive paint applied

Dip, flow, spray

Poor spray gun technique

Spray

Distorted spray gun pattern

Spray

Air pressure too low

Spray

Withdrawal from paint too rapid

Dip

Automatic equipment is jerky

Dip, flow

Drafts

Dip

Improper racking

Dip, flow, spray

Streaking

Metal too hot or too cold

Dip, flow, spray

Poor spray technique; insufficient overlap between passes, should be 50%

Spray

Distorted spray pattern

Spray

Water spotting

Rain or dew settling on finish

Dip, flow, roller, spray

Washing before paint is completely dry

Dip, flow, roller, spray

Uneven quenching of hot surface

Roller

Wrinkling

Excessive film thickness

Dip, flow, roller, spray

Abnormally hot or humid drying environment, air drying only

Dip, flow, roller, spray

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