Paint and Coatings Defects Dictionary: E-H

Definitions, Causes, Prevention, and Corrective Action

The E-H section of the AirSprayTech Paint and Coatings Defects Dictionary covers defects involving surface contamination, corrosion, color separation, trapped air, gloss, coverage, and discontinuities in the coating film.

Several of these conditions can look alike. A whitish deposit may be efflorescence, chalking, blooming, or another form of contamination. A small circular opening may be a fisheye, crater, pinhole, or holiday. Identify the coating chemistry, substrate, exposure, and application history before deciding on a repair.

Safety reminder: Follow the coating and equipment manufacturers' instructions. Use the required ventilation, grounding, respiratory protection, personal protective equipment, and pressure-relief procedures. Evaluate existing coatings and corrosion products before sanding, heating, or removal.

Edge Failure

Definition:
Edge failure is premature coating breakdown at sharp edges, corners, welds, fasteners, or other changes in surface geometry where adequate film thickness is difficult to maintain.

What it looks like:
The coating becomes thin, rusts, cracks, lifts, or wears through first along edges and projections while nearby flat surfaces remain protected.

Common causes:

• Coating pulling away from a sharp edge because of surface tension
• Insufficient stripe coating or poor spray-gun angle
• Sharp, burred, or poorly prepared edges
• Low dry-film thickness
• Mechanical wear or concentrated environmental exposure

Prevention:
Round or break sharp edges when the specification requires it. Clean and prepare welds, corners, and fasteners, apply the specified stripe coat, approach complex geometry from multiple angles, and verify dry-film thickness.

Corrective action:
Remove corrosion and poorly bonded coating, restore the specified surface preparation, stripe-coat the affected geometry, and rebuild the coating system.

Related defects: Bridging, holidays, rust breakthrough, and thin film.

Efflorescence

Definition:
Efflorescence is a crystalline, usually whitish deposit formed when water dissolves soluble salts within masonry, concrete, plaster, or another porous material and carries them to the surface as it evaporates.

What it looks like:
White, gray, or colored powdery crystals appear on the surface or beneath a coating. The deposit may be localized along cracks and joints or spread across a larger area.

Common causes:

• Moisture moving through a salt-containing substrate
• Groundwater, leaks, condensation, or poor drainage
• Coating masonry or concrete before it has dried adequately
• Soluble salts in the substrate, repair materials, or water

Prevention:
Correct moisture entry and drainage problems. Allow new masonry or concrete to cure and dry as specified. Test and prepare the surface according to the coating manufacturer's requirements.

Corrective action:
Stop the moisture source before recoating. Remove deposits using an approved dry or wet-cleaning method, allow the substrate to dry, verify surface condition, and apply a compatible breathable or moisture-tolerant system when specified.

Related defects: Chalking, blistering, peeling, and moisture staining.

Erosion

Definition:
Erosion is the gradual wearing away or loss of coating material caused by weather, abrasion, fluid movement, particles, chemicals, or repeated cleaning.

What it looks like:
The film becomes thinner, rougher, faded, or locally worn through. High-exposure areas may reveal the primer or substrate first.

Common causes:

• Wind-driven dust, sand, rain, or ice
• Mechanical abrasion, traffic, washing, or material handling
• High-velocity liquid, slurry, or particle impingement
• Chemical attack or ultraviolet degradation
• Coating selection or film thickness inadequate for service

Prevention:
Select a coating system with the necessary abrasion, weather, and chemical resistance. Apply the required film thickness and protect high-wear areas with suitable design, maintenance, or sacrificial layers.

Corrective action:
Remove loose or degraded material, inspect the remaining thickness and substrate, repair damaged areas, and apply a system suited to the actual exposure.

Related defects: Chalking, fading, wear-through, and weathering.

Fading

Definition:
Fading is the gradual loss or change of coating color caused by pigment, binder, or surface degradation.

What it looks like:
The finish becomes lighter, duller, less saturated, or different in hue. Areas with greater sunlight or chemical exposure may change faster.

Common causes:

• Ultraviolet exposure
• Pigments or binders with inadequate exterior durability
• Heat, chemicals, weather, or repeated cleaning
• Chalking that changes the apparent color
• Uneven film thickness or cure

Prevention:
Specify lightfast pigments and a coating system rated for the expected ultraviolet, heat, chemical, and weather exposure. Maintain uniform application and curing conditions.

Corrective action:
Clean the surface to determine whether chalk or contamination is changing its appearance. Polishing may temporarily improve some finishes. Permanent color loss generally requires surface preparation and recoating with a more durable system.

Related defects: Chalking, discoloration, gloss loss, and yellowing.

Featheredge Splitting

Definition:
Featheredge splitting is cracking or lifting along the tapered boundary where a repaired coating has been sanded into an existing finish.

What it looks like:
Fine cracks, rings, lifting, or visible mapping appear around the perimeter of a repair after priming, topcoating, or curing.

Common causes:

• Weak, brittle, swollen, or poorly bonded material left at the repair edge
• Incompatible primer, solvent, or topcoat attacking the old finish
• Insufficient feathering or an abrupt film-thickness transition
• Excessive primer or topcoat thickness over the edge
• Inadequate flash time

Prevention:
Remove all weak material, taper the repair into a sound coating, use compatible repair products, apply controlled coats, and observe flash and cure times.

Corrective action:
Sand beyond the visible split until the complete edge is sound and stable. Rebuild the repair using the approved primer and topcoat procedure.

Related defects: Edge mapping, lifting, cracking, and sinkage.

Filiform Corrosion

Definition:
Filiform corrosion is corrosion that advances beneath a coating in narrow, thread-like tracks, commonly on coated aluminum and sometimes other metals.

What it looks like:
Fine, worm-like or thread-shaped lines spread beneath the film from scratches, cut edges, fasteners, or other coating breaks.

Common causes:

• Moisture and salts reaching the metal through a coating defect
• Inadequate cleaning, conversion treatment, or priming
• Damage at edges, holes, seams, scratches, or fasteners
• Humid service conditions
• Soluble contamination remaining beneath the coating

Prevention:
Clean and pretreat metal correctly, control soluble contamination, use a compatible primer and topcoat system, protect edges and fasteners, and repair damage promptly.

Corrective action:
Remove the coating beyond all visible corrosion tracks, eliminate corrosion products and contamination, restore the specified pretreatment, and reapply the complete coating system.

Related defects: Undercutting, rust creep, edge failure, and delamination.

Fisheyes

Definition:
Fisheyes are small, circular wetting defects caused when coating recedes from localized contamination or a low-surface-energy spot.

What it looks like:
Round depressions or openings form in the wet film, often with a small contaminant at the center and a raised ring around it.

Common causes:

• Silicone, oil, grease, wax, polish, or release agent
• Oil or moisture in compressed air
• Contaminated rags, gloves, tools, containers, hoses, or spray guns
• Airborne contamination from nearby operations
• Residue from improper cleaning products

Prevention:
Eliminate contamination throughout the finishing process. Maintain clean, dry compressed air, isolate silicone products, use approved cleaners, and keep mixing and spray equipment dedicated and clean.

Corrective action:
Remove the affected coating as required, identify and eliminate the contamination source, reclean the surface, and recoat. Additives should be used only when approved; they do not replace contamination control.

Related defects: Cissing, cratering, crawling, and poor wetting.

Flaking

Definition:
Flaking is the detachment of small, flat pieces of coating from the substrate or from another coating layer because adhesion or cohesion has failed.

What it looks like:
Loose chips or scales fall from the surface and expose an undercoat, primer, or substrate. Edges around the exposed area may continue lifting.

Common causes:

• Poor surface preparation or contamination
• Incompatible coating layers
• Applying outside the recoat window
• Moisture, corrosion, or soluble salts beneath the coating
• Aging, brittleness, impact, or excessive film thickness

Prevention:
Prepare the substrate correctly, maintain compatibility and cleanliness, observe recoat windows, control environmental conditions, and apply the specified film thickness.

Corrective action:
Remove all loose and poorly bonded material to a sound edge or substrate. Correct contamination, moisture, corrosion, or compatibility problems before recoating.

Related defects: Adhesion failure, delamination, lifting, and peeling.

Flash Rusting

Definition:
Flash rusting is the rapid formation of a thin layer of rust on freshly cleaned steel after exposure to moisture or a waterborne coating.

What it looks like:
Light orange, brown, or reddish corrosion develops quickly across the steel surface or appears through a wet or newly dried coating.

Common causes:

• High humidity, condensation, rinse water, or rain on freshly prepared steel
• Delay between surface preparation and coating
• Waterborne coating contacting reactive steel
• Soluble salts or contaminated cleaning water
• Insufficient airflow or drying

Prevention:
Control humidity and dew point, dry the surface promptly, minimize the delay before coating, use clean water and approved inhibitors when specified, and select a coating intended for the prepared steel and conditions.

Corrective action:
Follow the coating specification. Remove unacceptable rust and contamination, restore the required surface preparation, dry the steel, and recoat within the permitted time.

Related defects: Rust breakthrough, underfilm corrosion, and staining.

Floating

Definition:
Floating is the separation of pigments in a wet coating primarily in a vertical direction, causing one pigment to concentrate near the surface and change the apparent color.

What it looks like:
The surface color differs from the intended mixture, sometimes uniformly and sometimes with variations caused by film thickness or drying conditions.

Common causes:

• Differences in pigment size, density, surface treatment, or compatibility
• Improper mixing or reduction
• Excessive film thickness
• Uneven solvent evaporation or drying
• Formulation instability

Prevention:
Mix material thoroughly, maintain approved reduction and agitation, apply a uniform film, and follow the manufacturer's temperature and drying recommendations.

Corrective action:
Confirm that the material was mixed and applied correctly. Affected cured work generally requires surface preparation and recoating with properly mixed, stable material.

Related defects: Flooding, mottling, color variation, and pigment separation.

Flooding

Definition:
Flooding is the horizontal separation of pigments within a wet coating, producing uneven color across the surface.

What it looks like:
Patches, streaks, cells, or color variations develop across the same coated plane. The color may shift with film thickness, flow, or drying rate.

Common causes:

• Pigments with different movement or compatibility in the wet film
• Improper mixing, tinting, or reduction
• Excessive film thickness or uneven application
• Solvent imbalance, convection, or uneven evaporation
• Formulation instability

Prevention:
Use properly formulated material, mix and agitate as directed, maintain uniform viscosity and film thickness, and control application and drying conditions.

Corrective action:
Verify material condition and application variables. Sand or otherwise prepare the cured finish as required, then recoat with properly mixed material under uniform conditions.

Related defects: Floating, mottling, color variation, and pigment separation.

Foaming

Definition:
Foaming is the formation of many stable air or gas bubbles in a liquid coating during mixing, pumping, application, or cure.

What it looks like:
A frothy layer or mass of small bubbles appears in the container or wet film. Bubbles that remain during cure may leave pinholes, craters, roughness, or a porous film.

Common causes:

• High-speed mixing or excessive agitation
• Air entering a pump suction line or vortexing into the inlet
• Return flow splashing above the material level
• Porous substrates releasing air
• Incorrect viscosity, additive, solvent, or application method
• Coating chemistry that stabilizes entrained air

Prevention:
Mix and circulate without drawing air into the material. Keep suction connections tight, submerge return lines when appropriate, control agitation, seal porous surfaces, and use approved defoamers only as directed.

Corrective action:
Stop the source of air, allow the material to de-aerate if permitted, and correct viscosity or process conditions. Cured defects may require sanding, filling, or recoating.

Related defects: Bubbling, cratering, pinholing, and solvent popping.

Gloss Variation

Definition:
Gloss variation is an unintended difference in sheen across a coated surface or between adjacent parts.

What it looks like:
Glossy, satin, or dull patches appear in the same finish. Lap marks, spray passes, repair areas, or porous sections may be visible under reflected light.

Common causes:

• Uneven film thickness, overlap, gun distance, or atomization
• Insufficient mixing of flattening agents
• Porous or unevenly sealed substrate
• Different reducer, viscosity, flash time, or curing conditions
• Dry spray, overspray, contamination, or polishing differences
• Mixing batches or components inconsistently

Prevention:
Mix thoroughly, maintain uniform viscosity, apply consistent overlap and film thickness, seal porous surfaces, and control flash, temperature, humidity, and cure.

Corrective action:
Allow full cure before evaluation. Polishing may correct some gloss differences when permitted. Persistent variation generally requires uniform surface preparation and recoating.

Related defects: Die-back, dry spray, mottling, orange peel, and sinkage.

Grinning or Poor Hiding

Definition:
Grinning, also called poor hiding, occurs when the substrate, primer, repair, or previous color remains visible through the finish coat.

What it looks like:
Color or contrast from the underlying surface shows through the topcoat. Edges, repairs, stripes, and variations in primer shade may remain visible.

Common causes:

• Insufficient dry-film thickness or too few coats
• Over-reduction or low material solids
• Poor coverage from incorrect tip, nozzle, pressure, overlap, or technique
• Large contrast between substrate and topcoat colors
• Using the wrong primer or ground-coat color
• Inadequate mixing or pigment settlement

Prevention:
Use the recommended primer or ground-coat shade, mix thoroughly, apply the specified number of coats and film thickness, and maintain consistent overlap and fluid delivery.

Corrective action:
Allow the existing film to flash or cure as required, then apply additional compatible coating within the recoat instructions. Severe or uneven work may need sanding and recoating.

Related defects: Color variation, low film thickness, mottling, and transparency.

Haze

Definition:
Haze is a loss of clarity that gives a clear or glossy coating a cloudy, smoky, or veiled appearance without necessarily producing a distinct white blush.

What it looks like:
Reflections appear less sharp, and the finish may look dull or cloudy at certain viewing angles. Haze may be within the film or on its surface.

Common causes:

• Moisture, solvent, or microscopic air trapped in the film
• Incompatible materials or incomplete mixing
• Fine surface texture, dry spray, or polishing marks
• Contamination or residue on the surface
• Improper cure, excessive film thickness, or environmental exposure

Prevention:
Use compatible materials, maintain correct mixing and thickness, control humidity and temperature, allow proper flash and cure, and keep the surface and compressed air clean.

Corrective action:
Determine whether the haze is surface residue, texture, moisture, or an internal film problem. Cleaning or polishing may correct surface haze. Internal haze may require sanding and recoating under controlled conditions.

Related defects: Blooming, blushing, die-back, dry spray, and gloss loss.

Holidays

Definition:
Holidays are discontinuities where a coating film is missing, too thin, porous, or otherwise unable to provide continuous coverage. They are especially important in protective and lining systems.

What it looks like:
Bare spots, pinholes, skips, voids, thin edges, or invisible electrical discontinuities interrupt the coating. Approved holiday-detection equipment may be needed to locate them.

Common causes:

• Incomplete spray coverage or poor access to complex geometry
• Insufficient film thickness
• Pinholes, porosity, bubbling, or solvent popping
• Contamination, cissing, or fisheyes
• Sharp edges, welds, seams, fasteners, and difficult recesses
• Damage during handling, inspection, or assembly

Prevention:
Use correct spray technique, stripe-coat difficult geometry, measure film thickness, maintain lighting and access, and inspect each coat. When specified, perform holiday testing with the correct instrument and voltage for the coating thickness and type.

Corrective action:
Mark each discontinuity, prepare the repair area, and apply compatible repair material according to the specification. Retest repaired areas when required.

Related defects: Edge failure, pinholing, poor hiding, porosity, and skips.

E-H Troubleshooting Summary

Start by deciding whether the defect is on the surface, within the coating, beneath the coating, or a complete break in the film. Efflorescence begins with moisture and soluble salts in a porous substrate. Fisheyes begin with localized wetting failure. Floating and flooding involve pigment separation. Foaming involves stable entrained air. Holidays describe discontinuities rather than one single failure mechanism.

Document substrate preparation, coating batches, mixing, viscosity, pot life, spray setup, wet- and dry-film thickness, temperature, humidity, dew point, flash time, and cure. For protective systems, record edge preparation, stripe coating, thickness readings, and holiday-test results.

Continue the Defects Dictionary

• A-B: Adhesion failure through bubbling
• C-D: Chalking through dry spray
• E-H: Edge failure through holidays
• I-M: Intercoat contamination through mud cracking
• N-R: Nibs through runs
• S-Z: Sagging through wrinkling
• Powder Coating Defects: A separate guide to powder application and curing defects

Need Help Troubleshooting a Coating Defect?

Azimuth Spray Systems can help evaluate spray equipment, fluid delivery, compressed-air requirements, application settings, and finishing-process problems. Call 817-490-1777 or email [email protected].

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