Failures & Defects

Troubleshooting Coatings

Coating Failures

Causes & Remedies

Recognizing the type of coating failure encountered in the field, understanding its cause and how to remedy it can lead to early correction and/or major reductions in maintenance costs while maintaining the overall appearance. All coatings eventually fail by weathering, especially exterior weathering. However, premature failure is a costly problem that occurs all too frequently. This document addresses its probable cause and then gives methods of remedy.

 

Description

Causes

Remedy

CD01
ABRASION DAMAGE. Mechanical damage
Physical damage by abrasion (also impact)
Provide fendering protection; spot repair and use more abrasion or impact-resistant coatings
APPLICATION MARKS.
Poor quality tools. Temperature too hot causing paint to cure too quickly and not allowing the product to flow naturally.
Abrade back to flat even surface and refinish, considering applications and temperature conditions.
CD02
BLISTERING. Small to large broken or unbroken bubbles; surface may feel like sandpaper 
Surface contamination prior to paint application. Solvent entrapment due to paint being applied too thickly or overcoated too soon. Moisture entrapment during coating. Coating applied when humidity was too high.
Blowers in enclosed areas to accelerate solvent release; adequate cleaning of surface contamination; proper levels of cathodic protection; abrade back all blisters, fill where necessary and recoat.
CD03
BLUSHING. Flat finish with milky appearance
Moisture condensation in high humidity with fast evaporating or unbalanced thinner in spray application
Abrade back until blushing is cleared and recoat, consider the relative humidity and temperature; respray with retarder add to thinner
CHALKING. Poor gloss, powdery surface
Prolonged exposure to Ultra Violet rays, poorly mixed paint
For a permanent cure, abrade back and recoat ensuring the paint is properly mixed.
CD04
CHECKING. Narrow breaks, usually short, in topcoat that exposes undercoat
Limited coating flexibility, too thick a coat, or applied at too high a temperature
Sand or mechanically remove checked coat and apply fresh coat
CD05
COATING APPLIED TO DAMP SURFACE. Heavy wrinkling
Moisture on substrate distorts wet film
Remove by scraping or sanding and recoat under dry conditions
CD06
CRACKING. Deep cracks in coating that exposes substrate
Coating shrinkage, limited flexibility, excessive thickness, or applied/cured at too high a temperature
Sand, blast, or mechanically remove total coating and apply new coat
CD07
CRATERING. Also called pitting. Small, uniform indentations in film
Air pockets trapped in wet film during spraying
Sand or blast to smooth finish and apply additional coats
CRAZING. Appearance of shattered glass
Extreme temperature changes during coating, incompatible overcoating, coating applied too thickly or overcoated too soon
Abrading back and repainting may solve the problem, however, it is more likely that the complete coating needs to be removed and an appropriate coating re-applied in accordance with recommended specification
CD08
DELAMINATION. Peeling from undercoat or substrate
Separation/lifting of paint from chalky substrate or smooth, poor-bonded undercoat
Sand or mechanically remove all loose paint, clean and roughen smooth surface, and recoat
CD09
FISH EYES. Small holes in the coating film. Separation or pulling apart of wet film to expose underlying finish or substrate
Application over oil, dirt, silicone, or incompatible coating
Abrade back until contaminated area can be de-greased, allow to dry and recoat
CD10
IRREGULAR SURFACE DETERIORATION. Deterioration at edges, corners, crevices, channels, etc.
Difficult to coat surfaces, or configurations that permit collection of moisture, salt, and dirt
Round edges, fillet weld seams and crevices, avoid configuration that permits collection of contaminants, provide drainage
LIFTING OR PEELING. Paint lifting or peeling from surface
Poorly prepared surface, incompatible overcoating, moisture on the surface, or overcoating times exceeded
Remove loose coating, abrade, de-grease and recoat in accordance with recommended specification
LOSS OF GLOSS.
High humidity, cold conditions, and dewfall will cause the coating to cure with a low gloss level; Ultra Violet degradation over a period of time
Abrade back and recoat
CD11
MUD CRACKING. Deep, irregular cracks, looks like dried mud
A relatively inflexible coating applied too thickly
Remove coating and abrasively blast steel before reapplying at lesser thickness, sanding/mechanical cleaning may be acceptable on older substrates
CD12
ORANGE PEEL. Hills, valleys in coating resembling an orange peel
Paint too viscous, gun too close to surface, solvent evaporated too fast, or air pressure too low for proper atomization
Before cure, brush out excess coating and modify spray conditions. After cure, abrade back to an even flat surface and recoat. If using a roller, it may be necessary to lay off using a brush or pad after roller application.
CD13
OVERSPRAY. Also called dry spray. Dry, flat, pebbly surface
Particles reaching surface not wet enough to level because of too rapid solvent evaporation, gun too far from surface, or coating particles falling outside spray pattern
Before cure, remove by dry brush followed by solvent wiping. After cure, sand and apply another coat
CD14
PEELING OF THICK, INFLEXIBLE COATING. Peeling of thick paint from substrate
Stress from cured, weathered (contracted) coating exceeds adhesion to substrate
If limited, spot-remove loose coating and apply flexible coating; if extensive, scrape, grit blast, mechanically or chemically remove coating to substrate before recoating
CD15
PINHOLING. Tiny, deep holes exposing substrate
Insufficient coating spray atomization, coarse atomization, or settled pigment
If uncured, brush out and apply additional coat. If cured, apply additional coat
CD16
PINPOINT RUSTING. Rusting at pinholes or holidays
Pinholing or too high a steel surface profile for coating thickness
Use holiday detector for early detection of pinholes, apply additional coats after mechanical or blast cleaning
RUNS. Running of wet paint into uneven rivulets
Paint has been over-thinned or too much paint applied
Abrade back to an even, flat surface and recoat
CD17
SAGS. Also called runs or curtains. Excess flow of paint
Spray gun too close to work, paint applied too thickly, too much thinner, or surface too hard or glossy to hold the coating
Before cure, brush out excess coating and modify spray condition. After cure, abrade back to an even, flat surface and recoat
CD18
UNDERCUTTING. Blistering and/or peeling of coating where exposed steel is rusting
Corrosion products formed where steel is exposed, undermining and lifting coating
Early detection of defects with holiday detector and correction, use inhibitive pigments in primer
CD19
UNEVEN GLOSS. Nonuniform sheen, shiny spots
Nonuniform film thickness, moisture in film, temperature change during curing, or paint applied over soft or wet undercoat
Allow to dry and apply another finish coat under acceptable conditions for moisture and humidity
CD20
WRINKLING. Rough, crinkled surface
Surface skinning over uncured coating because of too much thickness and/or too warm weather causing solvent entrapment (uncured paint) under the surface
Scrape off wrinkles and apply thinner coat, avoid intense sunlight

Coating Defects

1.0   GENERAL

Defects present in applied coatings/linings can lead to premature failure. Therefore, it is essential to conduct a proper inspection to avoid placing a coating/lining into service when such defects are present.

2.0   DESCRIPTIONS OF COMMON DEFECTS

2.1 Alligatoring

Appearance — coating appears to be cracked, it has an appearance similar to alligator skin, the defects usually do not penetrate to the steel substrate
Causes — insufficient drying of coating before application of the second coat, coating applied and cured at too high a temperature,  excessive coating thickness, or coating cures too quickly

2.2  Blistering

Appearance — area of localized coating swelling, sometimes resembling bubbles
Causes — coating applied over too hot a surface, condensation forms at the coating/metal interface, trapped solvent, oil, grease or rust under the coating. Coatings and linings placed into service may blister due to degradative processes, e.g., those due to osmotic forces, cathodic disbondment or trapped solvent

2.3 Blushing

Appearance — coating finish has a dull, milky appearance
Causes — moisture condensation in a high-humidity environment, condensation on a cold surface

2.4 Chalking

Appearance — coating loses its gloss and usually develops a white, powdery surface
Causes — general weathering of the coating in atmospheric environments (i.e., ultraviolet degradation of the coating)

2.5 Cracking

Appearance — discontinuities/breaks, usually sharp in nature, in the coating that exposes the substrate
Causes — insufficient drying of coating before application of the second coat, coating applied and cured at too high a temperature, excessive coating thickness, coating cures too quickly, especially a thick coating/lining that is rapidly heated

2.6 Cratering

Appearance — small, uniform indentations in the coating/lining.
Causes — oil or moisture are present in the air lines during spraying (conventional), air pockets trapped in wet coating during spraying

2.7 Disbondment

Appearance — loss of adhesion to the substrate or between coats
Causes — early disbondment of the topcoat or the complete coating system is usually due to poor surface preparation; e.g., substrate or intercoat contamination, excessive cure time between coats. For heat-cured MarineLINE, excessive heating can sometimes lead to coating disbondment due to high coating thickness, surface contaminants or excessive flexing of the substrate.

2.8 Dry Spray

Appearance — surface of coating has a rough texture and porous appearance
Causes — poor atomization of the spray, spray guy is too far from the surface during application, high air temperature and low humidity can lead to rapid solvent evaporation thus producing partially dry spray particles

2.9 Foreign Inclusions

Appearance — foreign particles are embedded or partially embedded in the coating/lining
Causes — dust, dirt or abrasives that settle into coating while it is still wet, the sources for solid particle contamination can be airborne, from adjacent structures, equipment or dirty scaffolding, tracked in by personnel, etc.

2.10  Fish Eyes

Appearance — separation of the coating/lining film that resembles holes or deep depressions, can also be separation of the wet film just after application
Causes — application of the coating/lining over oil, dirt, moisture, silicone residue or other contaminants that reduce the wetting of the coating film over the substrate, coating over incompatible coatings

2.11 Missed Areas

Appearance — presence of localized bare areas on an otherwise coated item
Causes — missed regions are usually associated with difficult to coat areas

2.12 Orange Peel

Appearance — finely dimpled surface texture that resembles the skin of an orange
Causes — usually due to poor atomization of spray of low pressure, sometimes associated with fast solvent evaporation or spray gun positioned too close to the surface

2.13 Overspray

Appearance — a deposit of wet or dry coating particles on areas other than those intended to be coated
Causes — coating material that drifts onto other areas coated areas of the structure due to the configuration of the structure, e.g., “I” beams, or material that is carried by the wind or falls along walls of a vessel from elevated sections to the floor or lower sides.

2.14 Pinholing

Appearance — small diameter, deep holes that penetrate either through the coating/lining to the substrate or through the topcoat to the basecoat, often referred to as “holidays.”
Causes — coating applied over pits in the substrate, dry spray, embedded abrasives and dirt, solvent entrapment, hot substrates and incorrect viscosity of the coating material

2.15 Pinhole Rusting

Appearance — rusting that occurs at defects through coating/lining
Causes — defects present in coating/lining, e.g., pinholes, cracks, embedded particles, metal slivers in substrate that protrude into coating/lining, weld splatter or insufficient coating coverage over high points in the surface profile

2.16 Runs and Sags

Appearance — excess coating material that runs down vertical surfaces
Causes — coating applied at too high of thickness, excessive thinning of the material, application made to cold surfaces or poor air flow across coating in high relative humidity environments (i.e., retards solvent evaporation)

2.17 Softness

Appearance — coating dries on the surface but remains soft in the interior of the coating, one can indent the coating with a fingernail or leave a fingerprint when pressing on the coating
Causes — excessive coating/lining thickness, insufficient drying time, drying hindered by low temperatures and high humidity, poor ventilation which slows solvent evaporation

2.18 Tackiness

Appearance — coating/lining has only partially set and has a sticky feel but is not wet
Causes — excessive thinner, insufficient drying, cold temperatures, poor ventilation

2.19 Wrinkling

Appearance — coating/lining has a rough, crinkled texture
Causes — excessive coating thickness and temperature is too warm or cold

3.0 INSPECTION PROCEDURES

3.1 Examination of Coating Defects: Most defects are visible to the unaided eye. However, a low power pocket microscope can enhance the details of suspected defects. Flashlights or spotlights are required for inspections inside tanks, vessels, pipes, etc. They are also useful in other areas where natural lighting is poor. Utility, pocket or putty knives can be useful for examining coating adhesion loss due to flaking or peeling. Be careful not to damage the coating/lining. Dry film thickness readings should be made regularly over the coated structure according to the appropriate application procedures.

3.2  When to Inspect: The coating shall be inspected after each spray and stripe coat and before the next step in the coating operation. Also, all repairs and touch-ups must be inspected during and after completion.

3.3  Unacceptable Defects: The inspector is to use his/her discretion in determining which defects are unacceptable and those that are acceptable, however, the acceptance of a defect(s) shall in no way compromise the integrity of the coating/lining. This implies that the applicable application procedures shall be followed, otherwise, a non-conformance document must be prepared and authorized by the owner’s representative and the Technical Services Department at Advanced Polymer Coatings.

3.4  Marking Defects: Defects such as pinholes, low areas of dry film thickness, runs, sags, etc., can be identified using grease-free chalk, stone chalk or a suitable marking pen.

4.0 CORRECTIVE ACTIONS

All unacceptable defects shall be repaired according to the procedures provided in the appropriate applications procedure.

5.0  CONCERNS

5.1  Pinholes: Does spraying additional coats of material over pinholes adequately correct this defect? The answer to this question is no. Pinholes must be either removed or enlarged, and coating brushed into them and then overcoated by spray, brush or roller. See appropriate application procedures. Pinholes can reappear if material is not pushed down into the pinhole.

5.2 Excessive Thickness. Excessive dry film thickness or high thickness associated with runs and sags can eventually crack through organic movement or during heating curing.