Paint and Coatings Defects Dictionary: A-B
Definitions, Causes, Prevention, and Corrective Action
Paint and coating defects are rarely random. Most can be traced to the substrate, surface preparation, coating selection, mixing procedure, spray setup, application technique, environmental conditions, or curing process. Correctly naming the defect is the first step toward finding its cause and preventing it from happening again.
This AirSprayTech Academy dictionary explains common defects in practical terms. Because several defects can look alike, the visible symptom should be treated as a starting point rather than a final diagnosis. Review the coating manufacturer's technical data sheet before changing the product, application settings, or repair procedure.
How to Use This Dictionary
Each entry includes a definition, visible symptoms, common causes, prevention practices, corrective action, and related defects. When troubleshooting, document the coating batch, mixing ratio, reducer, viscosity, pot life, substrate temperature, air temperature, relative humidity, dew point, wet-film thickness, flash time, curing conditions, spray tip or fluid nozzle, and equipment pressures.
Safety reminder: Follow the coating and equipment manufacturers' instructions. Use the required ventilation, grounding, respiratory protection, personal protective equipment, and pressure-relief procedures. Never sand, heat, or disturb an unknown coating until its hazards have been evaluated.
Adhesion Failure
Definition:
Adhesion failure is the loss of bond between a coating and the substrate or between two coating layers. It can be localized or widespread.
What it looks like:
The coating may peel, flake, lift, chip, or separate in sheets. Failure at the substrate is commonly called adhesive failure. Separation within the coating itself is cohesive failure. Separation between coats is intercoat delamination.
Common causes:
- Oil, grease, dust, moisture, corrosion, silicone, or other surface contamination
- Inadequate cleaning or surface profile
- Applying an incompatible coating system
- Exceeding or missing the manufacturer's recoat window
- Applying over a glossy surface without the required abrasion
- Condensation on a surface at or below the dew point
- Improper mixing, induction, curing, or film thickness
Prevention:
Verify surface cleanliness, dryness, and profile before coating. Confirm compatibility among the substrate, primer, intermediate coat, and topcoat. Observe the specified temperature, humidity, dew-point separation, recoat window, mixing ratio, induction time, and film thickness.
Corrective action:
Determine where the separation occurred and identify the cause. Remove all poorly bonded material to a sound edge or sound substrate. Correct contamination, moisture, profile, or compatibility problems before rebuilding the specified coating system.
Related defects: Delamination, flaking, lifting, peeling, and undercutting.
Alligatoring
Definition:
Alligatoring is a severe cracking pattern that resembles the large scales of alligator skin. The top surface splits into irregular islands while the underlying layer may remain intact.
What it looks like:
Wide, interconnected cracks divide the coating into raised sections or islands. It is generally coarser and more pronounced than checking or crazing.
Common causes:
- Applying a hard, rigid topcoat over a softer or more flexible undercoat
- Applying another coat before the underlying layer has dried or cured adequately
- Excessive total film thickness
- Natural aging, oxidation, and repeated expansion and contraction
- Using incompatible coating types
- Applying coating under temperature conditions that prevent proper film formation
Prevention:
Use a compatible coating system and observe required dry times and recoat windows. Apply each coat within the recommended wet- and dry-film thickness. Avoid placing a rigid coating over a soft, uncured, or incompatible layer.
Corrective action:
Alligatoring usually cannot be corrected by applying another topcoat. Remove the failed layers to a stable coating or properly prepared substrate, then apply a compatible system at the specified thickness.
Related defects: Checking, cracking, crazing, mud cracking, and wrinkling.
Amine Blush
Definition:
Amine blush is a surface film that can develop while certain amine-cured epoxy coatings cure, particularly in cool or humid conditions. It results from reactions involving the amine curing agent, moisture, and carbon dioxide.
What it looks like:
The surface may feel greasy, waxy, or tacky and may appear cloudy, hazy, or discolored. Some blush is difficult to see but can still interfere with sanding, adhesion, or topcoating.
Common causes:
- High humidity during epoxy cure
- Low substrate or air temperature
- Condensation or moisture exposure
- Insufficient air movement
- Coating chemistry that is susceptible to blush formation
Prevention:
Apply and cure the epoxy within the manufacturer's environmental limits. Keep the substrate sufficiently above the dew point, provide appropriate air movement, and use a blush-resistant formulation when the service environment requires it.
Corrective action:
Follow the coating manufacturer's procedure. Amine blush is commonly removed by washing with clean water and an appropriate abrasive pad or approved cleaner before sanding. Sanding alone can spread or drive the contamination into the surface. Rinse, dry, and verify cleanliness before recoating.
Related defects: Blooming, blushing, intercoat adhesion failure, and surface contamination.
Bittiness
Definition:
Bittiness is a rough finish caused by small particles, skins, gelled material, dried coating, fibers, or other solid contamination deposited in the wet film.
What it looks like:
Small raised specks or hard particles are scattered across the surface. Unlike solvent popping or pinholing, bittiness adds material to the surface instead of leaving small openings.
Common causes:
- Dirty coating containers, pressure pots, pumps, hoses, or spray guns
- Failure to strain the coating
- Dried coating breaking loose from container walls, lids, or fluid passages
- Using material beyond its pot life or shelf life
- Poor housekeeping, airborne dust, clothing fibers, or booth contamination
- Incompatible materials forming gel particles
Prevention:
Maintain clean mixing and spraying equipment. Filter or strain coatings according to the manufacturer's recommendation. Keep containers covered, observe pot life, clean the spray area, and use compatible materials and solvents.
Corrective action:
After the coating cures, sand or polish minor defects if the coating system allows it. Severe contamination may require sanding and recoating. Find and remove the particle source before applying additional material.
Related defects: Dirt inclusions, nibs, seediness, and overspray.
Bleeding
Definition:
Bleeding is discoloration caused when soluble dyes, stains, pigments, or other color-forming substances migrate from an underlying material into a newly applied coating.
What it looks like:
Unwanted color appears in the topcoat as staining, streaking, yellowing, or a general color shift. The discoloration may return after another coat is applied if the source has not been isolated.
Common causes:
- Solvents in the new coating redissolving dyes or colorants below it
- Wood extractives, knots, marker ink, asphaltic materials, or stains migrating through the finish
- Applying an incompatible coating over an existing finish
- Insufficient sealing or use of the wrong primer
- Contamination remaining on or within the substrate
Prevention:
Identify substances that may migrate before coating. Clean the surface and apply a compatible stain-blocking sealer or primer when required. Test the complete coating system on a representative area before full production.
Corrective action:
Allow the coating to cure as directed, isolate the source with an approved barrier coat or stain-blocking primer, and reapply the finish. Severe cases may require removal of the affected coating and treatment of the substrate.
Related defects: Discoloration, staining, yellowing, and migration.
Blistering
Definition:
Blistering is the formation of raised, dome-shaped areas within or beneath a coating film because localized pressure or loss of adhesion lifts the film.
What it looks like:
Blisters may be isolated or grouped and can range from tiny bubbles to large swellings. They may contain air, moisture, solvent vapor, liquid, or corrosion products. The location and contents of a blister can provide important diagnostic evidence.
Common causes:
- Moisture beneath or moving through the coating
- Trapped solvent caused by excessive film thickness or inadequate flash time
- Application to a hot, damp, contaminated, or poorly prepared surface
- Osmotic pressure caused by soluble salts or contamination
- Heat exposure or rapid temperature changes
- Poor adhesion between coats or at the substrate
Prevention:
Confirm that the surface is clean, dry, and free of soluble salts and other contamination. Control wet-film thickness and flash time. Apply within the specified temperature, humidity, and dew-point limits, and correct sources of moisture intrusion.
Corrective action:
Open and examine representative blisters when safe to do so, determine where the failure occurred, and identify the pressure or adhesion source. Remove affected material, correct moisture or contamination problems, prepare the surface, and rebuild the specified coating system.
Related defects: Bubbling, delamination, osmotic blistering, peeling, and solvent popping.
Blooming
Definition:
Blooming is a dull, hazy, cloudy, or sometimes powder-like surface condition caused by moisture, incomplete cure, contamination, or the migration of a coating ingredient to the surface.
What it looks like:
The coating may lose gloss or develop a haze, film, or deposit. The appearance can resemble blushing, chalking, or amine blush, so the coating chemistry and exposure conditions must be considered.
Common causes:
- High humidity, condensation, or moisture during curing
- Low application or curing temperature
- Incomplete cure or incorrect mixing
- Incompatible coating components
- Migration of plasticizers, waxes, or other ingredients
- Airborne contamination or chemical exposure
Prevention:
Use compatible materials, mix accurately, and maintain the specified application and curing environment. Protect the wet film from condensation and contamination. Confirm the exact coating chemistry before choosing a preventive method.
Corrective action:
Identify whether the surface condition is moisture, contamination, incomplete cure, or ingredient migration. Follow the coating manufacturer's cleaning and repair instructions. Cleaning or polishing may restore some finishes; persistent or chemically affected films may require removal and recoating.
Related defects: Amine blush, blushing, chalking, dulling, and haze.
Blushing
Definition:
Blushing is a whitish, milky, or cloudy appearance that develops within a coating film. It is commonly associated with fast-drying solvent-based finishes such as lacquer.
What it looks like:
A normally clear or colored finish becomes cloudy, pale, or milky. The condition may affect a small area or the entire coated surface.
Common causes:
- Rapid solvent evaporation cooling the wet film
- High humidity allowing condensed moisture to become trapped in the film
- Incorrect or excessively fast thinner or reducer
- Low material or substrate temperature
- Excessive atomizing air or high air movement across the wet surface
Prevention:
Apply within the specified humidity and temperature range. Use the recommended thinner or reducer for the conditions, allow materials and parts to reach an appropriate temperature, and avoid excessive atomizing pressure or air movement.
Corrective action:
Follow the coating manufacturer's instructions. A light application of the recommended retarder or solvent may reopen some lacquer films and allow moisture to escape. A cured or severe defect may require sanding and recoating under controlled conditions.
Related defects: Blooming, haze, moisture entrapment, and loss of gloss.
Bridging
Definition:
Bridging occurs when a coating spans across a gap, crack, seam, fastener, or recessed area instead of fully contacting and conforming to the underlying surface.
What it looks like:
A thin film stretches across an opening or surface irregularity. The bridge may later crack, split, trap air or moisture, or leave an uncoated void beneath it.
Common causes:
- Coating viscosity or surface tension preventing penetration
- Applying excessive film thickness in one coat
- Spraying across narrow gaps, seams, threads, or sharp recesses
- Fast surface drying before the coating can flow into the opening
- Inadequate stripe coating, brushing, or application angle
Prevention:
Seal or fill gaps when required by the specification. Use stripe coats on seams, welds, edges, and difficult geometry. Select the correct viscosity and application method, approach recesses from multiple angles, and apply the specified film thickness.
Corrective action:
Remove unsupported or cracked coating, clean and prepare the exposed area, seal or fill the opening when appropriate, and recoat using a method that wets the complete surface.
Related defects: Holidays, edge failure, cracking, pinholing, and voids.
Bubbling
Definition:
Bubbling is the formation of bubbles in a liquid or partially cured coating film. It often occurs during mixing, application, flow, or early cure. The term is sometimes used loosely for blistering, but the mechanisms can be different.
What it looks like:
Visible bubbles appear in the wet film or rise to the surface. If they break but the coating does not flow closed, they can leave craters, pinholes, or a rough texture.
Common causes:
- Air incorporated by high-speed or improper mixing
- Air entrained by a leaking suction line, vortexing pump inlet, or cavitating pump
- Excessive agitation or returning circulating material above the fluid level
- Porous substrates releasing air into the wet film
- Excessive film thickness or viscosity that prevents bubbles from escaping
- Rapid cure or surface skinning
- Foaming caused by coating chemistry or contamination
Prevention:
Mix without drawing unnecessary air into the material. Keep pump suction connections tight, maintain adequate material level, control agitation, and use the manufacturer's recommended viscosity and film thickness. Seal porous substrates when required and allow mixed material to stand or de-aerate when permitted.
Corrective action:
Correct the source of entrained air before continuing. Depending on the coating and cure stage, minor wet-film bubbles may flow out. Cured defects may require sanding, filling, or removal followed by recoating.
Related defects: Blistering, cratering, foaming, pinholing, and solvent popping.
A-B Troubleshooting Summary
The appearance of a defect does not always reveal its cause. A cloudy film could be blooming, blushing, amine blush, incomplete cure, or contamination. A raised area could result from trapped solvent, moisture, osmotic pressure, corrosion, or simple air entrainment. Diagnose the complete coating system and process before selecting a repair.
When possible, retain a sample of the failed part and record the application conditions. Photographs, wet- and dry-film measurements, batch information, and spray settings can turn guesswork into useful evidence.
Planned Paint and Coatings Defects Dictionary
- A-B: Adhesion failure through bubbling
- C-D: Chalking through dry spray
- E-H: Efflorescence 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 for application and curing defects specific to powder finishing
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. For assistance, call 817-490-1777 or email [email protected].
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