Paint and Coatings Defects Dictionary: C-D
Definitions, Causes, Prevention, and Corrective Action
Coating defects that begin with C and D include surface deterioration, cracking patterns, contamination-related defects, loss of adhesion, gloss changes, and spray-application problems. Several can look similar even though their causes and repairs are different.
Use each visible symptom as a starting point. Review the substrate, surface preparation, coating compatibility, mixing procedure, spray setup, film thickness, flash time, and curing environment before selecting a corrective action.
Safety reminder: Follow the coating and equipment manufacturers' instructions. Use the required ventilation, grounding, respiratory protection, personal protective equipment, and pressure-relief procedures. Evaluate the hazards of existing coatings before sanding, heating, or removing them.
Chalking
Definition:
Chalking is the formation of a loose, powdery residue on the surface of a coating as the binder degrades and releases pigment or extender particles.
What it looks like:
A colored or whitish powder transfers to a hand, cloth, or adjacent surface when the coating is rubbed. The finish may also fade, lose gloss, or become thinner over time.
Common causes:
- Normal weathering caused by ultraviolet light, moisture, and oxygen
- Using a coating without sufficient exterior or ultraviolet resistance
- Extended exposure beyond the coating's service life
- Improper formulation, thinning, mixing, or cure
- Chemical or environmental exposure that attacks the binder
Prevention:
Select a coating designed for the expected ultraviolet, weather, and chemical exposure. Apply and cure it at the specified film thickness and mixing ratio. Maintain the coating system before severe binder erosion occurs.
Corrective action:
Remove loose chalk by the cleaning method recommended for the substrate and coating system. Verify that the surface is sound and free of residue before recoating. Severe deterioration may require removal to a stable layer or substrate.
Related defects: Blooming, fading, erosion, loss of gloss, and weathering.
Checking
Definition:
Checking is the development of short, narrow surface cracks that generally do not penetrate through the complete coating system.
What it looks like:
Fine, shallow cracks appear in a regular or irregular pattern. Checking is usually less severe than cracking and much finer than alligatoring.
Common causes:
- Loss of flexibility as a coating ages
- Excessive film thickness
- A rigid topcoat over a softer undercoat
- Repeated expansion and contraction of the substrate
- Premature recoating or incomplete cure
- Ultraviolet, thermal, or chemical degradation
Prevention:
Use a compatible, sufficiently flexible coating system. Observe dry-film thickness, recoat windows, and curing conditions. Select a product suited to the substrate movement and service environment.
Corrective action:
Sand or remove the checked coating to a sound layer. If the cracking extends deeper than expected, remove the complete failed system. Correct compatibility, thickness, or movement problems before recoating.
Related defects: Alligatoring, cracking, crazing, and mud cracking.
Cissing
Definition:
Cissing is the failure of a wet coating to uniformly wet the surface. The coating pulls away from small areas and exposes the substrate or underlying coat.
What it looks like:
Small circular or irregular openings develop in the wet film. They may resemble craters or fisheyes and often have a visible center where the coating has receded.
Common causes:
- Silicone, oil, grease, wax, polish, or release-agent contamination
- Water or oil carried by the compressed-air system
- Contaminated cleaning rags, solvents, mixing tools, or spray equipment
- Surface-tension differences between incompatible materials
- Contamination settling onto the surface before or during application
Prevention:
Eliminate the contamination source instead of relying on additives to hide it. Clean and prepare the surface with approved products, maintain the compressed-air system, isolate silicone operations, and keep mixing and spray equipment clean.
Corrective action:
Allow the coating to reach the stage specified by its manufacturer, then remove the affected material. Clean the surface thoroughly, correct the contamination source, and recoat. Applying more coating over active contamination may make the defect worse.
Related defects: Cratering, crawling, fisheyes, and poor wetting.
Cobwebbing
Definition:
Cobwebbing is the formation of fine, string-like filaments during spraying. The material stretches into threads instead of breaking into normal droplets.
What it looks like:
Web-like strands float through the spray area or collect on the part, booth, gun, or surrounding equipment. The deposited finish may feel rough or fibrous.
Common causes:
- Material viscosity that is too high for the spray setup
- Very rapid solvent evaporation
- Incorrect thinner or reducer
- Excessive atomizing air pressure
- Cold material or unsuitable coating chemistry
- Fluid nozzle, air cap, or spray technology mismatched to the coating
Prevention:
Use the coating manufacturer's recommended viscosity, solvent blend, temperature range, fluid nozzle, air cap, tip, and pressure settings. Do not reduce material outside the approved limits.
Corrective action:
Stop spraying and confirm viscosity, material temperature, reducer selection, and equipment setup. Clean deposited fibers from the work area. Sand and recoat affected parts if the cured surface cannot be repaired by the approved finishing procedure.
Related defects: Dry spray, overspray, poor atomization, and stringing.
Cracking
Definition:
Cracking is the splitting of a coating film because stresses exceed its strength or flexibility. Cracks may affect only the topcoat or extend through the entire coating system.
What it looks like:
Visible lines, splits, or networks of fractures appear in the finish. Edges may lift, expose an underlying layer, or provide a path for moisture and corrosion.
Common causes:
- Excessive film thickness
- Coating applied over an uncured or incompatible layer
- Loss of flexibility from age, ultraviolet exposure, or chemical attack
- Substrate movement, vibration, thermal cycling, or impact
- Incorrect mixing ratio or insufficient cure
- Applying a hard topcoat over a softer coating
Prevention:
Select a compatible coating system with the flexibility needed for the substrate and service. Control film thickness, mixing, cure, and recoat timing. Address structural movement rather than expecting a rigid coating to bridge an active crack.
Corrective action:
Determine how deeply the cracks extend. Remove failed material to a sound layer or substrate, repair active substrate cracks when required, and apply a compatible system at the specified thickness.
Related defects: Alligatoring, checking, crazing, mud cracking, and splitting.
Cratering
Definition:
Cratering is the formation of small, bowl-shaped depressions in a coating film. The film may become thin at the center or pull away enough to expose the layer below.
What it looks like:
Round depressions resemble tiny volcanic craters. A central speck or contaminant may be visible. The defect can appear individually or across a large area.
Common causes:
- Oil, silicone, grease, wax, or other low-surface-tension contamination
- Dirty compressed air, spray equipment, containers, or filters
- Air or gas bubbles breaking at the surface without adequate flow-out
- Incompatible coating materials or additives
- Dust particles or overspray landing in the wet film
Prevention:
Control contamination throughout the finishing area. Maintain clean, dry compressed air; use dedicated mixing tools and containers; follow approved cleaning procedures; and verify compatibility before introducing additives or different coating materials.
Corrective action:
Identify whether the crater was caused by contamination or a bursting bubble. Remove or sand the affected coating as required, eliminate the source, clean the surface, and recoat. Do not assume a fisheye eliminator is a substitute for contamination control.
Related defects: Cissing, fisheyes, pinholing, solvent popping, and bubbling.
Crazing
Definition:
Crazing is a dense network of very fine surface cracks. The cracks are usually shallower and more closely spaced than checking or general cracking.
What it looks like:
The surface develops a fine, web-like or hairline crack pattern. It may initially be visible only under magnification or at certain viewing angles.
Common causes:
- Internal shrinkage stress during drying or curing
- Excessive film thickness
- Fast surface drying over a softer underlying film
- Incompatible coating layers
- Aging, ultraviolet exposure, thermal cycling, or chemical attack
- Insufficient flexibility for substrate movement
Prevention:
Apply compatible materials within their specified thickness and recoat windows. Provide the required flash and cure conditions, and select a coating with adequate flexibility and environmental resistance.
Corrective action:
Sand or remove the crazed layer to a sound surface. If the defect extends through several coats, remove the failed system. Correct the thickness, compatibility, or curing problem before recoating.
Related defects: Checking, cracking, alligatoring, and stress cracking.
Crawling
Definition:
Crawling is severe wetting failure in which a liquid coating retracts into beads, islands, or patches and leaves substantial areas uncovered.
What it looks like:
The wet coating gathers together instead of remaining as a continuous film. Exposed areas can be much larger and more irregular than typical fisheyes or cissing.
Common causes:
- Heavy oil, wax, silicone, grease, or release-agent contamination
- An extremely smooth or low-surface-energy substrate
- Incompatible undercoat and topcoat
- Excessive coating surface tension
- Applying over a wet, glossy, or improperly prepared surface
Prevention:
Thoroughly clean and prepare the substrate, remove contamination, abrade glossy surfaces when specified, and confirm coating compatibility. Test the system on difficult plastics, composites, and previously coated surfaces.
Corrective action:
Remove the affected coating, eliminate the contamination or wetting problem, prepare the surface correctly, and reapply the compatible coating system.
Related defects: Cissing, cratering, fisheyes, and poor wetting.
Delamination
Definition:
Delamination is the separation of one coating layer from another or the separation of the complete coating system from the substrate.
What it looks like:
Coating lifts, peels, flakes, or separates in sheets. Examination of the back of the failed film can help identify the layer where adhesion was lost.
Common causes:
- Surface contamination or inadequate preparation
- Applying outside the recoat window
- Incompatible coating layers
- Moisture, soluble salts, corrosion, or trapped solvent
- Insufficient surface profile or failure to abrade a cured layer
- Improper mixing, cure, or environmental conditions
Prevention:
Document and inspect each stage of surface preparation and coating application. Maintain cleanliness, profile, dew-point separation, mixing accuracy, recoat timing, and specified film thickness.
Corrective action:
Determine the exact plane of failure. Remove every poorly bonded layer, correct contamination or compatibility problems, restore the required surface preparation, and rebuild the approved coating system.
Related defects: Adhesion failure, flaking, lifting, peeling, and undercutting.
Die-Back
Definition:
Die-back is a reduction in gloss that develops as a newly applied coating dries or cures. The finish may initially appear glossy and then become duller or uneven.
What it looks like:
Gloss decreases after application, sometimes in patches. Surface texture, porosity, or sanding marks may become more visible as the film cures.
Common causes:
- Solvent absorption into a porous substrate or undercoat
- Insufficiently cured or excessively absorbent primer
- Excessive or incorrect reducer
- Improper flash time or application technique
- Low film thickness, poor flow, or dry spray
- Moisture, low temperature, contamination, or incomplete cure
Prevention:
Seal porous surfaces, allow primers and undercoats to cure, use the recommended reducer, observe flash times, and apply a uniform film within the specified thickness and environmental range.
Corrective action:
Allow the coating to reach full cure before judging gloss. If permitted, polish minor die-back. More severe defects may require sanding, resealing the substrate or undercoat, and recoating.
Related defects: Dulling, gloss variation, sinkage, blooming, and dry spray.
Dirt Inclusions
Definition:
Dirt inclusions are foreign particles trapped in or deposited on a coating film during application and cure.
What it looks like:
Raised specks, fibers, dust, lint, hair, dried coating, abrasive residue, or other particles interrupt an otherwise smooth finish.
Common causes:
- Dirty parts, booth surfaces, floors, filters, garments, or equipment
- Unfiltered coating or contaminated containers
- Dried material breaking loose from hoses, guns, lids, or pressure pots
- Poor air filtration or excessive booth turbulence
- Dust generated by nearby sanding, grinding, or traffic
- Static attraction on the part
Prevention:
Control cleanliness throughout the process. Clean parts and equipment, strain material, maintain booth filters and airflow, separate dirty operations, wear suitable garments, and control static as required.
Corrective action:
Remove the contamination source. After cure, nib-sand and polish minor defects if the coating permits. Severe contamination may require sanding and recoating.
Related defects: Bittiness, nibs, seediness, and surface contamination.
Discoloration
Definition:
Discoloration is any unintended change in coating color, tone, clarity, or uniformity during application, curing, or service.
What it looks like:
The finish may yellow, darken, fade, stain, develop patches, or shift from the approved color standard. The change can be localized or uniform.
Common causes:
- Ultraviolet, heat, chemical, smoke, or moisture exposure
- Bleeding or migration from the substrate or undercoat
- Incorrect mixing, tinting, reduction, or batch combination
- Contamination in the coating, equipment, or compressed air
- Uneven film thickness, application method, or cure
- Using a binder or pigment not suited to the service environment
Prevention:
Specify materials with suitable color and environmental resistance. Standardize mixing, application, film thickness, and cure. Use compatible primers and sealers, clean equipment, and verify color before full production.
Corrective action:
Identify whether the change is caused by the coating, substrate, contamination, exposure, or application. Correct the source. Cleaning or polishing may restore some finishes; permanent changes usually require surface preparation and recoating.
Related defects: Bleeding, fading, mottling, staining, and yellowing.
Dry Spray
Definition:
Dry spray occurs when atomized coating droplets lose too much solvent, fail to remain wet, or do not flow together after reaching the surface.
What it looks like:
The finish appears rough, grainy, dusty, dull, or sandy. Overspray may sit loosely on the surface, and gloss or color can be uneven.
Common causes:
- Gun held too far from the workpiece
- Excessive atomizing air or fluid pressure
- Incorrectly fast thinner or reducer
- High booth temperature, low humidity, or excessive air movement
- Viscosity too high or fluid delivery too low
- Spray tip, fluid nozzle, or air cap mismatched to the coating
- Poor gun angle, excessive travel speed, or overspray from adjacent passes
Prevention:
Maintain the correct gun distance, angle, overlap, and travel speed. Use the coating manufacturer's recommended viscosity and reducer for the conditions. Select the proper spray setup and use only the pressure necessary to achieve acceptable atomization.
Corrective action:
Correct the spray distance, pressure, viscosity, reducer, airflow, or equipment setup. A minor wet-film defect may accept another properly timed pass if the product instructions allow it. A cured rough finish may require sanding or polishing followed by recoating.
Related defects: Cobwebbing, orange peel, overspray, poor atomization, and rough finish.
C-D Troubleshooting Summary
Before changing spray pressure or adding reducer, determine whether the defect began at the substrate, within the coating system, at the spray gun, or during cure. Cissing and crawling usually point toward poor wetting or contamination. Cobwebbing and dry spray often point toward viscosity, solvent evaporation, equipment setup, or technique. Checking, cracking, and crazing usually involve stress, compatibility, thickness, movement, or aging.
Record the coating batch, mixing ratio, viscosity, pot life, tip or fluid-nozzle size, air-cap selection, fluid and atomizing pressures, gun distance, film thickness, temperature, humidity, dew point, flash time, and curing conditions. These details make comparisons and recurring-defect analysis much more reliable.
Continue the 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 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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