Macro Defects in Steel - Coating Defects

Coating Defects

Abrasion
Description: The mechanical action of rubbing, scraping, scratching, gouging or erosion.
Probable Causes:Removal of a portion of the surface of the coating or in severe cases removal to expose the substrate by contact with another object such as the use of metal chains for lifting, cargo, fenders, or the grounding of a ship.
Prevention:Use of abrasion resistant coatings formulated with particular regard to resins and extender pigments. With severe cases of abrasion the effects will only be reduced or limited by an abrasion resistant coating.
Comment:Depends on the extent of the damage and could range from individual areas prepared by mechanical cleaning to the blast cleaning of large areas. Application of an abrasion resistant coating.
Adhesion Failure

Paint fails to adhere to substrate or underlying coats of paint..
Probable Causes:Surface contamination or condensation, incompatibility between coating systems and exceeding the overcoating time.
Prevention:Ensure that the surface is clean, dry and free from any contamination and that the surface has been suitably prepared. Use the correct coating specification and follow the advised overcoating times.
Repair:Depends upon the extent of adhesion failure. Removal of defective areas will be necessary prior to adequate preparation and application of correct coating system to manufacturer’s recommendations.
Alligatoring (also known as Crocodiling)

Very large (macro) crazing/cracking which resembles the skin of an alligator or crocodile. Cracks may penetrate through to the undercoat or down to the substrate.
Probable Causes:Internal stresses in the coating where the surface shrinks faster than the body of the paint film. Excessive film thickness and limited paint flexibility. Application of a hard topcoat over a more flexible softer undercoat. Application of topcoat before the undercoat has dried.
Prevention:Use correct coating specification and compatible materials. Avoid excessive film thickness. Avoid application at high ambient temperatures.
Repair: Repair will depend upon size and extent of alligatoring. Abrade or remove all affected coats and apply suitable undercoat and topcoat. Follow recommended application procedures.
Aluminium Corrosion

Blistering and/or lifting/disruption of the paint coating due to the formation of aluminium corrosion products under the paint.
Probable Causes:Pinholes in the coating. Porosity of flame/ arc sprayed aluminium. Insufficient coating thickness.
Prevention:Use correctly formulated coating system applied at the correct thickness as a closed film.
Repair: Blast clean and recoat.
Application Defects

Defects associated with application by brush e.g. brush hairs in the coating, contamination from rollers, fingering and spattering from spray application.
Probable Causes:Poor quality brushes and rollers, incorrect brush and roller materials, incorrect spray setup and inadequate care during application.
Prevention:Use good quality equipment of the correct type and follow the data sheet guidelines.
Repair: Repair is related to the type and extent of the defect but often rubbing down and recoating is adequate.
Bittiness (also known as Peppery, Seedy or Seedi-ness)

Film contaminated by particles of paint skin, gel, flocculated material or foreign matter which project above the surface of the paint film to give a rough appearance. The term Peppery is used when the bits are small and uniformly distributed.
Probable Causes:The main cause is contamination within or on the surface of the paint film. This can be paint skin, gelled particles, airborne material and grit or contamination from brushes, rollers etc.
Prevention:Use clean application equipment and clean working environment. Use new, uncontaminated paint. Follow good painting practices.
Repair:Repair depends on size and extent of problem. Abrade or completely remove the contaminated layer and recoat.
Bleaching

Total loss of colour of a coating.
Probable Causes:Weathering or exposure to chemicals.
Prevention:Use colour stable pigments or a system which will withstand the chemical environment.
Repair:Remove bleached coating or abrade and recoat using a more suitable coating system.
Bleeding (also known as ‘Bleed Through’)

Staining of a paint film by diffusion of a soluble coloured substance from the underlying paint to give undesirable discoloration or staining . Often seen where bituminous or tar based products are overcoated with topcoats in which the tar or bitumen is soluble. Also occurs with emulsion paints.
Probable Causes:‘Bleed Through’ is generally a full or partial redissolving of the previous coat or an ingredient of a previous coat and can occur when strong solvents are used in the topcoats.
Prevention:Use correct coating specification and materials. Use compatible materials. Use appropriate sealer coat if possible.
Repair:Remove stained or contaminated layer. Apply a suitable sealer coat which will prevent the diffusion of soluble coloured material from beneath. It may be possible to apply a sealer coat without the removal of the stained/contaminated layer.
Blistering (General)

Dome shaped projections or blisters in the dry paint film through local loss of adhesion and lifting of the film from the underlying surface. Blisters may contain liquid, vapour, gas or crystals.
Probable Causes:Many mechanisms can be involved including osmotic gradients associated with soluble salts, soluble pigments, corrosion products, retained solvents and solvents from cargoes. Non-osmotic blistering associated with electro endosmosis, cathodic disbonding, thermal gradients related to cold wall effects and compressive stress.
Prevention:Ensure correct surface preparation and application. Apply a suitable coating system after testing for soluble salts. Consider the possibility of the different blister mechanisms in the particular environment.
Repair:Depending upon size and type of blistering, remove blistered areas or entire coating system and repair or fully recoat.
Blistering - Intercoat

Dome shaped projections or blisters in the dry paint film through local loss of adhesion from an underlying coating.
Probable Causes:Commonly the presence of soluble salt contamination between coats or soluble material in the underlying coats.
Prevention:Ensure that tests for soluble salts are carried out if contamination is suspected and fresh water wash if necessary
Repair: Depending upon size and type of blistering, remove blistered areas or entire coating system, fresh water wash and repair or fully recoat.
Blistering – Non-Osmotic

Dome shaped projections or blisters in the dry paint film through local loss of adhesion from the steel substrate.
Probable Causes: Non-osmotic blistering associated with electroendosmosis, cathodic disbonding, thermal gradients related to cold wall effects and compressive stress. Where electroendosmosis is involved, the blistering is often seen as a circular pattern of blisters around a coating defect where the substrate is exposed.
Prevention: Ensure correct surface preparation and application. Apply a suitable coating system after considering the possibility of the different blister mechanisms in the particular environment.
Repair: Depending upon size and type of blistering, remove blistered areas or entire coating system and repair or fully recoat.
Blistering – Osmotic

Dome shaped projections or blisters in the dry paint film through local loss of adhesion from an underlying coating.
Probable Causes: Osmotic blistering is commonly associated with the presence of soluble salts, soluble pigments, soluble corrosion products, retained solvents or the absorption and retention of low molecular weight water miscible solvents, typically from the carriage of chemical cargoes.
Prevention: Ensure correct surface preparation and application and follow working procedures for ventilation etc. Apply a suitable coating system after testing for soluble salts. Consider the possibility of the different blister mechanisms in the particular environment.
Repair: Depending upon size and type of blistering, remove blistered areas or entire coating system, fresh water wash and repair or fully recoat.
Bloom (Blush)

A hazy deposit on the surface of the paint film resembling the bloom on a grape, resulting in a loss of gloss and a dulling of colour.
Probable Causes: Paint film exposed to condensation or moisture during curing especially at low temperature (common phenomenon with amine cured epoxies). Incorrect solvent blend can also contribute to blooming.
Prevention: Apply and cure coating systems under correct environmental conditions and follow the manufacturer’s recommendations.
Repair: Remove bloom with clean cloth or suitable solvent cleaners. If necessary, apply undercoat/topcoat following manufacturer’s recommendations.
Bodying

An increase in the consistency/body of a coating that occurs during manufacture or storage often increasing the viscosity to a point that it is unusable.
Probable Causes: Incorporation of too much thixotrope or poor storage conditions.
Prevention: Correct raw material control and correct storage.
Repair: The coating is often unusable.
Bridging

The covering over of unfilled gaps such as cracks or corners with a film of coating material. This introduces a weakness in the paint film which may crack or flake off.
Probable Causes: Poor application. High viscosity paint system. Failure to brush paint into corners and over welds.
Prevention: Brush apply a stripe coat into corners and welds and fill all cracks or weld them prior to application of the full coating system.
Repair: Remove all loose paint, abrade the surface, apply a stripe coat by brush, fill and recoat.
Brush Marks (also Laddering, Ladders or Ropiness)

Undesirable ridges and furrows which remain in a dry paint film after brush application, where the paint film has not flowed out. May be found as a cross-hatch pattern (Laddering) where alternate coats have been applied in opposite directions. Pronounced brush marks are known as Ropiness.
Probable Causes: Viscosity of material may be too high for brush application; Incorrect thinners used; Inadequate mixing or poor application technique; paint has poor leveling properties; two-pack paints may have exceeded application pot-life.
Prevention: Use brushing grade of paint and apply adequate thickness. Thin paint to brushing viscosity. Use within pot-life.
Repair: Depending on extent of brush marks, thoroughly abrade surface and recoat with suitable viscosity paint.
Bubbles Or Bubbling

Bubbles within a paint film appear as small blisters. These may be intact or broken (to leave a crater). Can be found in excessively thick paint films, especially if spray applied, and also with roller application. This should not be confused with blistering.
Probable Causes: Trapped air/solvent within the coating which is not released before the surface dries. Air entrainment during mixing. High ambient temperature during application. Also seen when overcoating antifouling without removal of the leached layer and zinc silicates. Can be found with factory applied coatings where application is by dipping, electrodeposition or roller coating.
Prevention: Spray application - adjust viscosity with thinners and follow data sheet requirements for maximum application temperature. Use correct mixing equipment to ensure air is not stirred in during mixing. Apply a mist coat. Add defoaming agent to emulsion paints.
Repair: Depending on extent and severity of bubbling, abrade or remove the offending coat(s) and recoat.
Cargo Damage

Deformation or removal of a coating by physical action or chemical action.
Probable Causes: An example of physical action is the abrasive contact of a hard angular cargo on the holds of a bulk carrier and an example of chemical action is that of an aggressive chemical cargo on a tank lining.
Prevention: Use an abrasive resistant coating (in most cases this will reduce/limit but not prevent the abrasion) or a coating compatible with the cargo to be carried.
Repair: In the case of isolated mechanical damage, spot repair and touch up. In the case of extensive damage blast clean and recoat may be required.
Cathodic Disbonding

Blistering and delamination of a coating system around bare steel areas and coating defects associated with cathodic protection on buried pipelines, immersed structures and the hulls of ships.
Probable Causes: High overvoltage principally from impressed current systems but also to a lesser extent with sacrificial anodes when the number of anodes is excessive. Factors are incorrect installation, poor monitoring, and incompatible coating systems.
Prevention: Use a well designed cathodic protection system, regularly monitored with well placed reference electrodes and application of an alkali resistant coating system.
Repair: Eliminate the source of the overprotection. Blast clean the affected areas and apply a suitable coating system.
Chalking

A friable, powdery layer on the surface of a paint film. A change of colour or fading is also seen. Chalking rates vary with pigment concentration and choice of binder. Chalking is a known characteristic of certain paints e.g. epoxy paints.
Probable Causes: Disintegration of the paint binder on exposure to weathering and/or UV light.
Prevention: Apply a suitable topcoat with high resistance to chalking, and with UV resistance.
Repair: Remove all powdery deposits by wiping, scrubbing, high pressure washing or abrasion. Wipe loose material off and apply a chalk resistant topcoat.
Checking

Fine cracks which do not penetrate the topcoat of a paint system. Some checking can be so minute that it is impossible to see without magnification.
Probable Causes: Typically a formulation and/or a specification problem. As with cracking, stresses are developed which cause the surface of the paint film to become brittle and crack. Limited paint flexibility.
Prevention: Use a correctly formulated coating system.
Repair: Abrade and clean surface then apply an undercoat/topcoat to suit.
Cheesiness (Soft Coating)

Coating remains soft, even after prolonged drying time.
Probable Causes: Wrong mixing ratio for two-pack paints. Too low a drying/curing temperature. Excessive solvent retained within the coating.
Prevention: Ensure adequate mixing of two-pack paints. Only use the recommended amount of thinners. Apply and cure the coating under controlled environmental conditions.
Repair: Remove all soft coatings and apply suitable coating system or topcoat to coating manufacturer’s recommendations.
Chemical Exposure

Chemical breakdown of a coating after exposure to aggressive chemicals.
Probable Causes: The reaction of a coating with a chemical or atmosphere (either organic or inorganic) that it is not resistant to.
Prevention: Use coating systems suitable for the environment or prevent the chemical from reaching the coated surface.
Repair: Will depend on the extent of failure but removal or neutralization of the chemical and fresh water washing essential. Use a chemically resistant coating and consider isolation from the source of the chemical.
Cissing

Surface breaks in a wet paint film, where the paint has receded to expose the underlying substrate. The paint is unable to wet out the substrate. Can be very large.
Probable Causes: Surface contamination by either moisture or foreign matter such as oil, grease, silicone etc. Also known to happen when incorrect solvent blends have been used.
Prevention: Ensure surface is clean and free from grease, oil and foreign contaminants prior to application of coating.
Repair: Abrade and thoroughly clean the contaminated surface or remove the coating to achieve a clean surface. Reapply the coating system to the coating manufacturer’s recommendations.
Cobwebbing

The production of fine filaments instead of normal atomised particles when some solutions of high molecular weight polymers are sprayed. Traditionally when applying chlorinated rubber coatings by conventional spray.
Probable Causes: Too high a viscosity with some types of polymer solutions. Will occur with chlorinated rubber at almost any viscosity.
Prevention: Reduce the spraying viscosity. Select a more suitable solvent blend. Change the spraying conditions.
Repair: Abrade to remove all affected material and recoat.
Cracking

The splitting of a dry paint film through at least one coat to form visible cracks which may penetrate down to the substrate. Cracking comes in several forms, from minute cracking to severe cracking.
Probable Causes: Cracking is generally a stress related failure and can be attributed to surface movement, ageing, absorption and desorption of moisture and general lack of flexibility of the coating. The thicker the paint film the greater the possibility it will crack.
Prevention: Use correct coating systems, application techniques and dry film thicknesses. Alternatively, use a more flexible coating system.
Repair: Abrade to remove all cracked paint. Correctly reapply the coating system or use a more flexible system and one less prone to cracking.
Cracking At Welds

Paint coatings with visible cracks at weld seams which may penetrate down to the substrate.
Probable Causes: Cracking is generally a stress related failure and can be attributed to surface movement, ageing, absorption and desorption of moisture and general lack of flexibility of the coating. The thicker the paint film the greater the possibility it will crack. Also occurs when the adhesion of the coating is insufficient to bear the stress.
Prevention: Use correct coating systems, application techniques and dry film thicknesses or use a more flexible coating system.
Repair: Abrade to remove all cracked paint. Correctly reapply the coating system or use a more flexible system and one less prone to cracking.
Cratering

The formation of small bowl shaped depressions in the paint film. Not to be confused with Cissing.
Probable Causes: Trapped air or solvent bub-bles which have burst to leave small craters as the coating dries. The coating has insufficient time to flow into a uniform film.
Prevention: Improve spray technique, apply a mist coat and avoid air entrainment during mixing. Add thinners as rec-ommended by the paint supplier.
Repair: Abrade and clean the surface and recoat.
Crazing

Similar to checking but the cracks are generally wider and penetrate deeper into the film.
Probable Causes: Application temperature too low, incompatibility with previous coating, ageing and high film thickness.
Prevention: Apply a thinner coat of paint, add slower drying solvent, check application and drying conditions are correct for the paint system used and check compatibility.
Repair: Abrade and clean the surface and recoat.
Crowsfooting

The development of small wrinkles in the paint film which occur in a pattern resembling that of a crow’s foot.
Probable Causes: Usually due to the surface drying rapidly to form a skin which then wrinkles as solvent slowly evaporates from the soft underlying paint.
Prevention: Apply a thinner coat of paint; add slower drying thinners, check application and drying conditions are correct for the paint system used.
Repair: Abrade the surface when fully dry and recoat.
Dryspray

Rough and uneven finish to the surface of the paint film where the particles are insufficiently fluid to flow together and are often poorly adhered.
Probable Causes: Incorrect spray application i.e. gun distance. Also associated with fast drying products and too high an application temperature.
Prevention: Use correct coating application equipment and techniques. Use a slower drying solvent or solvent blend. Follow recommended application procedures.
Repair: Abrade and remove any loose dryspray and reapply coating or topcoat.
Edge Corrosion

Breakdown at edges resulting in corrosion.
Probable Causes: Low film thickness, sharp edges, lack of stripe coats and flow away from the edges.
Prevention: Ensure that all edges are radiused, stripe coats are applied and the coating has good edge retention.
Repair: Remove coating by abrading, radius the edges and reapply the coating system with adequate stripe coats.
Efflorescence

White (powdery) substance on the substrate of concrete, brick, masonry and plaster. The efflorescence, which comes from the migration of salts, can lift the paint from the substrate.
Probable Causes: Soluble salts within the substrate. Moisture brings the salts to the surface of the substrate resulting in coating adhesion failure.
Prevention: Ensure surface is moisture free, clean and suitable for application of the coating system. Remove or eliminate the source of moisture.
Repair: Remove all powdery substances and thoroughly clean the surface. Apply a suitable sealer and coating system formulated for concrete, masonry etc.
Erosion

Selective removal of paint films from areas or high spots.
Probable Causes: The wearing away of the paint film by various elements such as rain, snow, wind, sand etc. Found to be more prominent on brush applied coatings because of the uneven finish.
Prevention: Use a suitable coating system with resistance to surface erosion/abrasion.
Repair: Clean surface free from contamination and apply a coating system formulated and tested for the specific environment.
Exudation

The appearance of an oil-like film on the surface of the coating after drying. Also described as sweating but not to be confused when the term is used to explain condensation on a surface.
Probable Causes: Migration of a component of the coating e.g. plasticizer, additive, or curing agent that remained unreacted. Often associated with poor environmental conditions during or after application.
Prevention: Apply under good environmental conditions and use a more suitable coating.
Repair: Depends on the extent of the defect but may be resolved by solvent washing and re-application of a suitable topcoat under controlled environmental conditions.
Fading

Discolouration or gradual decrease in colour of paint when exposed to sunlight/weather. May be accompanied by loss of gloss. In some situations it may resemble chalking but without the powdery surface. Fading tends to accelerate in the presence of moisture.
Probable Causes: Incorrect pigmentation; use of non light stable organic pigments; atmospheric contamination; porous substrate.
Prevention: Use correct coating systems which resist UV light and fading. Use a coating with light stable pigments.
Repair: Abrade and clean the surface and apply a light stable coating system.
Fat Edge

An accumulation of a ridge of coating at an edge of the article being coated often occurring during drainage after dip application.
Probable Causes: Rheology of the coating not suitable for dip application.
Prevention: Re-formulate or use a more suitable coating.
Repair: Abrade the area and recoat.
Feather Edging

Bevelling/tapering the edges of a repair area of a coating by abrading to gradually reduce the thickness and expose the different underlying layers.
Probable Causes: Untreated edges of spot blast cleaned repair areas.
Prevention: Abrade all edges of spot blast cleaned repairs. This is only practical on small areas. On extensive spot blasting it is impractical.
Repair: Bevel/taper the edges to gradually expose previous coats and recoat.
Filiform (Corrosion)

Random threads of corrosion that develop beneath thin lacquers and other coating films from a growing head or point. Often seen on old ‘tin’ food cans, with thin electro plating but also on painted aluminium and other surfaces.
Probable Causes: Contamination on the metallic substrate or damage to the coating which allows a corrosion cell to develop at the tip and advance under the coating.
Prevention: Ensure no contamination exists on the substrate prior to coating application.
Repair: Remove all traces of corrosion products and non adhering coatings. Abrade, clean and coat to manufacturer’s recommendations.
Fish Eyes

Small quasi-circular areas of substrate that are exposed through the applied coating immediately after application and which have at their centre a source of contamination.
Probable Causes: Surface contamination in the form of small spots of wax, silicone, grease or particles from contaminated airlines.
Prevention: Thoroughly degrease the surface and maintain equipment.
Repair: Abrade the affected area, degrease and reapply the coating system. In automotive applications fish eye eliminators can be used.
Flaking

A form of adhesion failure where paint flakes from the substrate. A familiar sight on wood substrates and on galvanising.
Probable Causes: Incorrect paint system used. Either none or incorrect pre-treatment used for certain substrates i.e. non-ferrous or galvanised. Also poor application techniques. May also be attributed to differential expansion and contraction of paint and substrate e.g. wood. Can be the result of ageing of the paint system.
Prevention: Use correct coating system and pre treatment.
Repair: Remove all flaking coating until a firm edge can be achieved. Abrade, sweep blast and clean overall and apply suitable coating system to coating manufacturer’s recommendations.
Flocculation

The development of loosely coherent pigment agglomerates in a coating material.
Probable Causes: Non-uniform pigment dispersion which results in the pigments forming agglomerations. Unsuitable thinners or inadequate mixing. Can also occur in manufacturing.
Prevention: Ensure only properly formulated and mixed products are used. Use recommended thinners.
Repair: Remove coating where flocculation is visible. Abrade and clean the surface and apply a properly formulated and mixed coating system.
Flooding

A defect which appears soon after application due to pigment separation. The visual appearance is a deepening of the colour. The affected area dries to a deeper shade than the remainder of the surface.
Probable Causes: Pigment separation and settlement.
Prevention: Use correctly formulated products.
Repair: Lightly abrade and clean and then recoat with a suitably formulated material.
Flotation

Occurs in coloured materials containing mixtures of different pigments. It closely resembles flooding, although a mottled or streaky effect is produced when the different pigments separate.
Probable Causes: The mottled effect, which is visible to the eye, is caused by separation of the different coloured pigments. It may also result from the addition of excessive thinners.
Prevention: Use correctly formulated products. Do not over thin with solvent.
Repair: Abrade and clean overall and apply a suitable sealer or topcoat.
Galvanising (Loss of adhesion of coating)

Loss of adhesion to a galvanized substrate.
Probable Causes: Incorrect surface preparation or absence of an etch primer/”T-Wash”.
Prevention: Abrade weathered galvanizing or apply etch primer/”T-Wash” to fresh galvanizing after degreasing.
Repair: Remove detached paint, degrease, fresh water wash and abrade weathered galvanizing or apply etch primer/”T-Wash” to fresh galvanizing.
Grinning or ‘Grinning Through’

The underlying surface is visible through the paint film due to inadequate hiding power of the coating material. This is sometimes called ‘Grinning-Through’. Often seen where dark colours are overcoated with lighter colours.
Probable Causes: Low film thickness of penultimate coat. Poor opacity and covering power of topcoat. Strong colour of primer/undercoats.
Prevention: Apply adequate dry film thickness between individual coats. Use opaque coatings with good opacity.
Repair: Apply additional compatible coats to clean surface.
Grit Inclusions

Particles of grit and dust embedded within the coating system. The particles will rust if ferrous.
Probable Causes: Failure to remove used grit from the surface prior to application of the paint. Contamination of the wet primer or undercoat with grit from other blast cleaning operations. Windblown grit particles adhering to the topcoat.
Prevention: Ensure all used grit is removed before application of fresh paint. Do not carry out blast cleaning whilst there is wet paint on nearby surfaces. Ensure than all cans of paint and brushes etc. are protected during blast cleaning operations.
Repair: Abrade or blast clean the surface to remove all grit contamination, thoroughly clean the surface and recoat.
Growth (on the surface of a paint film)

Growth and attachment of organisms to the surface of finished products. These vary in form, size and lifespan, e.g. algae, mosses etc.
Probable Causes: Natural organisms associated with moist, wet or immersed conditions. Growth may continue after attachment.
Prevention: Use correct coating specification and products suitable for the environment. Where practical, clean regularly to prevent build-up of moss and algae.
Repair: Clean and remove all growth, abrade the surface and apply a suitable coating system.
Heat Damage

Discolouration, detachment and/or blistering and general degradation of a paint film.
Probable Causes: Effect of high temperature often applied to the reverse side of a steel plate from burning, welding or fire.
Prevention: Ensure that all welding/burning is completed prior to painting.
Repair: Abrade small areas or blast clean large areas prior to reinstating the coating system.
Impact Damage (Star cracking)

Cracks which radiate from a point of impact.
Probable Causes: Impact damage to a relatively brittle coating. Often seen on glass fibre reinforced plastics. Also occurs when steel is deformed by impact.
Prevention: Prevent impact damage.
Repair: Abrade all damaged areas and recoat.
Incorrect Coating System

An unsuitable or incompatible coating system has been used which results in rapid failure.
Probable Causes: Use of incompatible or unsuitable coating materials for the service required.
Prevention: Use correct coating specification and materials. Ensure that different coats are compatible with each other.
Repair: Remove all defective coating and apply correct coating system to manufacturer’s recommendations.
Incorrect Coating Thickness

A coating system that has been applied at inadequate thickness often leading to premature breakdown.
Probable Causes: Poor spray application, poor quality control and difficult access.
Prevention: Improve spray application and quality control.
Repair: Abrade area and overlaps and reapply to the correct thickness.
Intercoat Contamination

The presence of contamination between coats in a multi-coat system.
Probable Causes: The contamination could be present due to inadequate washing down, salts from weathering of shopprimer or deposits from nearby operations.
Prevention: Carefully inspect and test the surface before paint application and wash down with fresh water if required.
Repair: Abrade to remove poorly adherent paint, fresh water wash and recoat.
Knotting

Bleed through of resin/sap from knots in timber and staining of the surface with brownish marks.
Probable Causes: Knots not treated with knotting agent before painting.
Prevention: Treat knots with shellac based solution.
Repair: Clean area with methylated spirit, abrade and recoat.
Laminations Or Shelling

Sub-surface planar metallic defects appearing as isolated thin strips or layers with poor adhesion to the parent metal. Overpainting without treatment results in paint breakdown, rusting and rust staining.
Probable Causes: Laminations are associated with non-metallic inclusions which have been deformed during the rolling process and run in the direction of rolling. They are often only visible after blast cleaning.
Prevention: Use good quality steel plate and ensure proper surface preparation is carried out.
Repair: Grind all laminations to remove them and blast clean the surface and recoat.
Mechanical Damage

Paint removal by scraping and scratching from contact with external objects.
Probable Causes: Contact with anchor chains, fenders, grounding and use of chains rather than slings for lifting.
Prevention: Use abrasion resistant coatings to minimize damage and use appropriate lifting equipment.
Repair: Mechanically clean small areas and blast clean larger areas prior to recoating.
Milkiness

A milky white surface appearance that is apparent shortly after application and often seen on transparent varnish films.
Probable Causes: Moisture condensing on the film in humid conditions when the steel temperature is below the dew point. Can be aggravated by incorrect solvent balance.
Prevention: Ensure environmental conditions are as recommended in the data sheet.
Repair: Apply heat to the affected area or recoat after the environmental conditions have been corrected.
Millscale

The blue/black thin layer of iron oxides formed on the steel surface during the hot rolling process.
Probable Causes: Millscale is not uniform and not well adherent to the steel, hence if painted over will detach from the steel substrate together with the paint as moisture laden air penetrates beneath and/or differential expansion/contraction occurs.
Prevention: Abrasive blast clean to remove the millscale and impart a surface profile.
Repair: Abrasive blast clean and apply a suitable coating system.
Misses/Skips/Holidays

Exposed areas of substrate when the intention was to coat the entire area. Could be confined to a single coat in a multi-coat paint system.
Probable Causes: Poor application techniques. Lack of quality control. Poor access and design.
Prevention: Use correct application techniques. Apply good painting practices. Use qualified inspectors.
Repair: Apply coatings to suitably prepared and cleaned substrates to original specification and manufacturer’s repair procedures.
Missing Topcoat

Failure to apply the topcoat leaving the undercoat exposed.
Probable Causes: Poor coating application and quality control. Inadequate dry film thickness.
Prevention: Thoroughly inspect all surfaces to ensure each coat has been correctly applied.
Repair: Abrade the surface and either apply the topcoat, or an additional undercoat and topcoat, in accordance with the paint suppliers’ recommendations.
Mud Cracking

The dried paint film has the appearance of a dried-out mud flat. The cracks appear as a network that can vary in size and amount.
Probable Causes: Generally over application of heavily pigmented primers such as inorganic zinc silicates or water based coatings, although can occur with other over thick systems.
Prevention: Only apply the recommended coating thickness. Use recommended application techniques with suitably formulated products.
Repair: Remove all cracked and flaking paint back to a sound base. Abrade and clean or blast clean the surface. Reapply coating to manufacturer’s recommendations.
Orange Peel also known as Pock-marking

A uniform pock-marked appearance, in particular of a spray applied coating in which the surface of the paint film resembles the skin of an orange.
Probable Causes: Failure of the paint film to flow out. Usually caused by poor application techniques, by incorrect solvent blend or too high thixotropy.
Prevention: Use correct application techniques with suitably formulated products.
Repair: Where aesthetics are of concern, abrade overall, clean and recoat.
Overspray

Small particles of paint adhering to the surface of a previous dry coat, generally adjacent to the area being sprayed. Often appears as a pebbly surface.
Probable Causes: Particles of wet paint falling outside the spray pattern as misapplication to an adjacent surface. Spray application under windy conditions.
Prevention: Spray paint under suitable environmental conditions. Adjust spray pattern to minimise overspray.
Repair: Before curing or drying, remove by dry brushing followed by solvent wipe. After curing, abrade and apply a further coat.
Peeling

Similar to flaking, although peeling tends to be associated with soft and pliable fresh coatings which can be pulled away from or spontaneously flake away from the substrate or from between coats, due to loss of adhesion.
Probable Causes: Peeling is the reduction in bond strength of the paint film due to contamination or incompatibility of coats.
Prevention: Use correct coating system and specification applied to clean and uncontaminated surfaces.
Repair: Remove all soft and pliable coating back to a firm edge or total removal. Abrade, clean and apply suitable coating system to coating manufacturer’s recommendations.
Pinholes

The formation of minute holes in the wet paint film during application and drying, due to air or gas bubbles which burst, giving rise to small craters or holes which fail to coalesce before the film has set.
Probable Causes: Solvent or air entrapment within a paint film. A common problem when coating porous substrate such as zinc filled primers, zinc silicates and metal sprayed coatings. Pinholes can also be caused by incorrect spray application or incorrect solvent blend.
Prevention: Use correct application techniques with suitably formulated products. Correct solvent blends and environmental conditions. Check spray equipment and distance of spray gun from the surface. Apply a mist coat.
Repair: Abrade, clean overall and apply suitable tiecoat/undercoat and topcoat as necessary.
Primer Degradation

Deterioration of a shopprimer during weathering in the form of rust rashing and salt formation in the case of zinc silicate primers.
Probable Causes: Low film thickness, excessive exposure periods and harsh environmental conditions.
Prevention: Ensure that an even, adequate film thickness is applied and the exposure period is suitable for the environmental conditions.
Repair: Depending on the extent, the surface is either prepared by mechanical cleaning (small areas) or blast cleaning (large areas) prior to application of the coating system.
Rain Damage

Craters and water marks on the surface of the paint film caused by rain or heavy condensation.
Probable Causes: Rain falling on a freshly painted surface causes craters to form on the surface before it has hardened sufficiently.
Prevention: Allow coating (where practicable) to surface harden prior to exposure to rain or heavy condensation.
Repair: Abrade, clean all surface damage areas and apply overall undercoat/topcoat.
Rippled Coating

A rippled effect on the surface of the paint.
Probable Causes: Strong wind blowing across the surface of wet paint causes it to ripple. Where this is on the underside, the ripples can hang down in the form of small stalactites. Can also be caused by poor application techniques.
Prevention: Do not apply paint under unfavourable conditions. Use correct application equipment and workmanship.
Repair: When mild ripples are seen, abrade the surface and recoat. Where this is a major effect, remove the coatings and recoat.
Rot (wood)

Damp and rotten wood exposed by splitting, flaking and cracking of paint.
Probable Causes: Generally poor maintenance or application over soft and rotten wood. Occasionally, use of incorrect paint system.
Prevention: Correct and ongoing maintenance to the wood and coating. Ensure all wooden surfaces are sound and free from rot before application of paint.
Repair: Replace rotten wood, preferably with treated wood. Apply a suitable coating system formulated for wood surfaces.
Runs

A narrow downward movement of a coat of paint often apparent from accumulation of excessive quantities of paint at irregularities such as cracks and holes where the paint continues to flow after the surrounding surface has set.
Probable Causes: Over application of paint, excessive use of thinners, incorrect (lack of) curing agent or poor workmanship.
Prevention: Use correct application techniques and apply at the recommended dry film thickness.
While the paint is still wet, brush out runs and sags. (N.B. this does not restore the surface properly). When the paint has dried, abrade and clean defective areas and apply overall coat or spot repair, as necessary.
Rust Jacking

Formation of layers of rust scale that expand, increase in volume and force the mating surfaces apart.
Probable Causes: Penetration of moisture between mating surfaces through defects in the coating system.
Prevention: Edges of mating surfaces to be adequately coated and gaps to be sealed.
Repair: All corrosion products to be removed prior to the area being fresh water washed, recoated and gaps sealed.
Rust Rashing to Thermal Spray Coating

Spots of ferrous oxide develop within the pores of a sprayed metal coating similar to rust rashing of a paint film.
Probable Causes: A phenomenon which can develop on aluminium thermal sprayed coatings soon after application as moisture is absorbed into the metal coating and reacts with the ferrous substrate.
Prevention: Apply thermal spray coating in a controlled environment. Seal metal sprayed surface immediately after application.
Repair: Clean rust rashing locations, wire brush and fresh water wash. Providing dry film thickness of the thermal spray is adequate, apply sealer coat to coating manufacturer’s recommendations.
Rust Rashing

Fine spots of rust which appear on a paint film, often a thin primer coat. The initial spots rapidly spread over the surface resulting in a film of rust through which the individual spots are difficult to discern. Also from holidays.
Probable Causes: Low film thickness often in combination with a high surface profile.
Prevention: Ensure that an adequate thickness of a primer coat is applied to cover the surface profile and check that the surface profile is not too large.
Repair: Clean rust rashing locations, wire brush and fresh water wash. Large areas may require blast cleaning.
Rust Spotting

Individual spots of rust which appear on a paint film and frequently start as localised spotting but rapidly increase in density.
Probable Causes: Low film thickness (more likely creating rust rashing), voids and holidays (more likely creating rust rashing), but also defects in the steel such as laminations and inclusions. Too high a surface profile may cause penetration of peaks through a paint film and cause rust spotting. May also occur from metallic contamination of a coated surface by grinding dust etc.
Prevention: Ensure that an adequate thickness of a primer coat is applied to cover the surface profile. Use a thicker coating system or a lower blast profile. Protect coating from contamination with grinding dust etc.
Repair: Depending on type and extent, abrade or blast clean surface after removal of all foreign debris. Apply spot repair or recoat overall.
Rust Staining

A light staining on the surface of the paint caused by the precipitation of ferrous oxide from adjacent exposed steel.
Probable Causes: Water run-off from a rusty surface above a soundly coated surface. Rust staining occurs when the rust is wetted out and contaminated water runs over and discolours other items or locations. Usually more of an eye sore than a defect. The coating itself may not be defective, only stained.
Adequate design and suitable maintenance.
Repair: Remove staining with a rust remover and apply a cosmetic coating, as necessary.
Sags also described as curtains
Sags are the downward movement of a coat of paint which appear soon after application and before setting that results in an uneven area with a thick lower edge. They are usually apparent on local areas of a vertical surface and in severe situations may be described as curtains.
Probable Causes: Over application of paint, excessive use of thinners, incorrect (lack of) curing agent or poor workmanship. Could, in extreme circumstances, be a formulation problem.
Prevention: Use correct application techniques with suitably formulated products.
Repair: While the paint is still wet, brush out runs and sags although this may not result in an acceptable appearance. When the paint has dried, abrade and clean defective areas and apply overall coat or spot repair as necessary.
Salts

Contamination in the form of a salt.
Probable Causes: Deposition from a coastal salt laden environment, environmental pollution or weathering of zinc primers.
Prevention: Protect items from exposure during treatment and fresh water wash between coats if positive tests for salts are obtained.
Repair: If salts are detected fresh water wash prior to coating application.
Saponification

The coating appears to be soft and sticky. Can be in sporadic isolated spots or as an overall effect.
Probable Causes: The formation of a soap by the reaction between a fatty acid ester and an alkali. Decomposition of the binder component of alkyd and oil based coatings by alkali and moisture from a substrate such as concrete or cementitious renders. Can also occur on zinc substrates.
Prevention: Use correct coating specifications and materials.
Repair: Remove all soft coatings where saponification has occurred, abrade, clean and reapply undercoat/topcoat using non-saponifiable materials.
Settlement

The sedimentation of the solid constituents comprising pigments and extenders from the binder and solvent whilst standing in a container. Settlement which occurs after mixing and during application can result in different shades and performance in different areas.
Probable Causes: Old stock, heavily pigmented paint and incorrect formulation of product. Can be a problem with zinc rich primers.
Prevention: Use products within shelf life. Use adequate mixing procedures. Keep paint mixed or recirculated during spray application.
Repair: If a variation in shade is produced, abrade and reapply ensuring uniform mixing before and during application.
Skinning

Formation of a layer of skin on the paint surface in a container.
Probable Causes: Absence of anti-skinning agent, use of non airtight container, hot storage conditions. Often occurs in part used cans.
Prevention: Use airtight container and store according to data sheet.
Repair: Remove layer of skin and mix until homogeneous.
Solvent Lifting

Eruption of the surface of the paint film. Wrinkling and blistering which leads to a weak surface and ultimate coating breakdown.
Probable Causes: Incompatible paint systems used. Topcoats with a strong solvent blend can react with previous and weaker solvent blended coatings. Overcoating before the previous coat has adequately hardened.
Prevention: Use correct coating specification, overcoating times and materials. Conduct compatibility trials with undercoat/topcoats.
Repair: Remove all defective coatings. Abrade, clean and recoat with correct coating system, following the recommended overcoating times.
Solvent Popping

Solvent (clear) bubbles on the surface of the paint film soon after application.
Probable Causes: Incorrect solvent blends, porous surfaces and incorrect environmental conditions. High surface temperature.
Prevention: Use correct coating specifications and materials and ensure correct application techniques and environmental conditions.
Repair: Lightly abrade and clean the surface and apply undercoat/topcoat.
Staining

Discolouration of a coating system.
Probable Causes: Contact with a solid or liquid that imparts a discolouration or stain to the coating.
Prevention: Avoid contact with solids and liquids that are prone to cause staining or use dark coloured coatings where any staining would not be so apparent.
Repair: If the stains are on the surface they may be removed by washing with water or chemical cleaning agents. If the stains have penetrated the coating, abrading after washing may be required prior to recoating.
Stress Cracking

Paint coatings with visible cracks which may penetrate down to the substrate.
Probable Causes: Stress cracking can be attributed to surface movement, ageing, absorption and desorption of moisture, thermal cycling and general lack of flexibility of the coating. The thicker the paint film the greater the possibility that cracking might occur. Often occurs around welds and changes in section.
Prevention: Use correct coating systems, application techniques and dry film thicknesses or use a more flexible coating system.
Repair: Abrade to remove all cracked paint. Correctly reapply the coating system or use a more flexible system and one less prone to cracking.
Stripe Coats

Although not a defect the absence of stripe coats can lead to premature breakdown. A coat of paint applied by brush or roller to edges, welds, pits and other difficult to spray areas prior to application of the next full coat.
Probable Causes: Breakdown can occur from areas not stripe coated due to the tendency of a coating to flow away from an edge resulting in low film thickness. (The third photograph illustrates an area of poor stripe coating).
Prevention: Ensure adequate stripe coating is carried out prior to application of each full coat.
Repair: Apply additional stripe coats to areas with missing stripe coats or with inadequate film thickness.
Tackiness

Degree of stickiness remaining in the film. Although beyond the wet and liquid stage, the paint film remains as a tacky and soft surface. Sometimes only apparent on touching the coating.
Probable Causes: There are various reasons why a paint will remain tacky:
Over thickness;
Excessive thinners;
Wrong (lack of) curing agent;
Low drying/curing temperature;
Use of coating beyond pot life or shelf life.
Prevention: Use correct coating specifications and materials. Ensure two-pack materials are correctly mixed. Follow paint suppliers recommendations.
Repair: Remove defective coating. Abrade, clean and recoat.
Undercured Coating

A coating that is soft or tacky and easily deformed.
Probable Causes: Insufficient drying/curing time, curing in adverse environmental conditions, poor mixing of 2-pack coatings.
Prevention: Ensure that the manufacturers’ technical data sheet is followed and that the coating is fully cured before being placed in service.
Repair: Remove coating from the damaged area by abrasion and recoat. Large areas may require blast cleaning.
Undercutting

Visual corrosion beneath a paint film often called creep. Corrosion travels beneath the paint film and lifts the paint from the substrate. Severe cases can show as blistering, flaking, cracks and exposed rust.
Probable Causes: Application of paint to corroded substrate. Rust creep from areas of mechanical damage and missing primer coat. Can be found in areas of poor design or access where inadequate preparation and coating thickness was applied. Could also be due to lack of maintenance.
Prevention: Use adequate coating specifications and maintenance procedures. Apply a suitably formulated primer.
Repair: Spot repair localised areas.Clean areas back to a sound substrate and apply suitable repair coating to manufacturer’s recommendations.
Water Spotting

The spotty appearance of the paint film caused by drops of water on the surface and which remains after the water has evaporated. The effect may or may not be permanent.
Probable Causes: The marks formed by rain drops falling on a wet paint film are prone to leaving permanent marks after evaporation whereas rain drops falling on a freshly dried but hard surface are more likely to be able to be rubbed off although with epoxy coatings it may be more difficult.
Prevention: Do not apply paint when rain is forecast.
Repair: Where the marks are just on the surface these may be washed off but where there is cratering or permanent damage to the paint film, abrade the surface and recoat.
Wrinkling

The development of wrinkles in the paint film during drying.
Probable Causes: Usually due to the initial formation of a surface skin with solvent based paints. Can arise from overcoating before the previous coat has adequately hardened. Over thickness particularly with alkyd coatings.
Prevention: Use correct coating specification and materials and ensure adequate mixing, application and curing by following the paint suppliers’ recommendations.
Repair: Remove defective coatings. Abrade, clean and recoat.
Zinc Salts

The formation of zinc salts on a zinc rich coating or on a galvanised surface during weathering.
Probable Causes: Excessive period of weathering or exposure to an aggressive environment before overcoating. Coating application over zinc salts can lead to premature failure. Zinc silicate tank coatings exhibit salt formation in service but is not considered a problem.
Prevention: Reduce the weathering period, protect from an aggressive environment or apply an appropriate protective coating system.
Repair: Fresh water wash the surface to remove all traces of zinc corrosion products. Sweep blast or abrade, clean and apply a suitable coating system.