Why do coatings fail? Common failures, and how to solve them
Peeling, rusting, blistering, cracking, chalking, corrosion under the film, lost adhesion, pinholes, sagging, discolouration and erosion — what causes each one, how it is solved, and how it is prevented next time.
Coating failures are rarely about the product alone. Each of the failures below has a cause that can be identified — and prevented.
01Why does paint peel?Understanding adhesion failure
Peeling is one of the most visible signs of coating failure. The coating lifts, flakes or separates from the surface, sometimes exposing the underlying substrate.
Why does it happen?
Paint does not simply fail because of the product itself. Poor adhesion can result from:
- Inadequate surface preparation
- Dust, oil, grease or other contamination
- Moisture on the substrate
- Rust or mill scale left on the surface
- Incompatible coating layers
- Incorrect application or recoating conditions
How can it be solved?
The first step is to identify why the coating lost adhesion.
Loose and poorly bonded coating should be removed, followed by appropriate surface preparation. The substrate should then be assessed before selecting a compatible coating system and applying it according to the required application conditions.
How can it be prevented?
Good adhesion starts with a properly prepared surface. Surface cleanliness, surface profile, environmental conditions, coating compatibility and application procedures should all be considered before recoating.
Don’t just repaint a peeling surface. Find out why it lost adhesion first.
02Why does rust come back after painting?When corrosion returns beneath the coating
One of the most frustrating coating problems is seeing rust appear again after a surface has been painted. It may appear as small rust spots, staining, bubbling or eventually peeling of the coating.
Why does it happen?
Common causes include:
- Inadequate removal of existing rust
- Poor surface preparation
- Contamination or soluble salts
- Moisture
- Insufficient coating thickness
- Damage to the coating
- A coating system unsuitable for the environment
How can it be solved?
The affected area should be assessed to determine the extent of corrosion.
Failed coating and corrosion products should be removed, followed by the appropriate level of surface preparation. A suitable corrosion protection system can then be applied according to the substrate and environmental requirements.
How can it be prevented?
The coating system should be selected based on the expected environment and required durability. Proper surface preparation and sufficient coating thickness are equally important.
Rust prevention starts before the first coat.
03Why does paint blister?Understanding bubbles beneath the coating
Blistering occurs when bubbles or raised areas develop beneath the coating surface. Some blisters may appear small and harmless, but they can indicate a problem beneath the coating.
Why does it happen?
Blistering can be associated with:
- Moisture trapped beneath the coating
- Soluble salts or contamination
- Poor surface preparation
- Application under unsuitable environmental conditions
- Solvent entrapment
- Incompatible coating layers
How can it be solved?
Do not simply puncture or paint over the blisters. The cause should first be identified. Affected coating may need to be removed and the substrate inspected and properly prepared before recoating.
How can it be prevented?
Control the conditions before and during application. Important factors include:
Surface cleanliness · Moisture · Humidity · Temperature · Dew point · Coating compatibility
When a coating blisters, look beneath the surface.
04Why does paint crack?Understanding cracking and coating stress
Cracks can range from fine hairline patterns to deep cracks that expose the underlying substrate. Once cracks develop, moisture and contaminants may enter the coating system and accelerate deterioration.
Why does it happen?
Possible causes include:
- Excessive coating thickness
- Incorrect coating system
- Movement of the substrate
- Incompatible coating layers
- Poor substrate condition
- Ageing and weathering
- Incorrect application
How can it be solved?
The extent and cause of the cracking should be determined first. Unstable coating should be removed where necessary, the substrate corrected and a suitable coating system applied.
How can it be prevented?
Follow the recommended coating thickness and application procedures. The coating system should also be appropriate for the substrate and expected service conditions.
More coating does not always mean more protection. The right thickness matters.
05Why does paint chalk?When UV and weathering change the surface
Chalking appears as a fine, powdery residue on the coating surface. It is commonly noticed when a hand or cloth picks up powder from an exposed painted surface. Chalking can also be accompanied by fading or loss of gloss.
Why does it happen?
Chalking can occur as the coating binder gradually deteriorates under prolonged exposure to:
- UV radiation
- Sunlight
- Weathering
- Moisture
- Outdoor environmental conditions
How can it be solved?
The surface should be assessed and cleaned thoroughly. Depending on the severity of deterioration, the existing coating may be suitable for recoating after preparation, or more extensive removal may be required.
How can it be prevented?
Select a coating system suitable for the expected exposure. For outdoor applications, UV and weather resistance should be considered when choosing the coating system.
The right coating depends on the environment it must survive.
06Why is rust appearing under the paint?Understanding corrosion beneath the coating
Rust appearing beneath a coating can be a sign that corrosion has developed between the substrate and coating system. The visible rust may only represent part of the problem.
Why does it happen?
Possible causes include:
- Remaining rust or mill scale
- Inadequate surface preparation
- Moisture reaching the substrate
- Coating damage
- Insufficient coating thickness
- Poor edge and weld treatment
- Unsuitable coating system
How can it be solved?
The affected area should be inspected to determine the extent of corrosion. The failed coating and corrosion should be removed, followed by suitable surface preparation and application of an appropriate corrosion protection system.
How can it be prevented?
Pay attention to areas that are particularly vulnerable, including:
Edges · Welds · Joints · Crevices · Damaged areas
Proper preparation and coating application are essential for long-term corrosion protection.
A coating protects only where the system is properly prepared and applied.
07Why do coatings lose adhesion?Looking beyond the visible failure
Poor adhesion occurs when the coating does not bond properly to the substrate or to the previous coating layer. It can result in peeling, flaking, lifting or delamination.
Why does it happen?
Common contributing factors include:
- Poor surface preparation
- Dust, oil, grease or moisture
- Incorrect surface profile
- Incompatible coating layers
- Recoating outside the recommended interval
- Incorrect application conditions
- Poor substrate condition
How can it be solved?
The failed interface should be identified first. Poorly bonded coating should be removed and the remaining surface assessed. The substrate should then be prepared appropriately before applying a compatible coating system.
How can it be prevented?
Before coating, consider the complete system:
Each stage contributes to overall coating performance.
A coating system is only as strong as its weakest interface.
08Why do pinholes appear?Small holes in the coating film
Pinholes show up as small holes in the coating film. They can look minor, but each one is a break in the barrier the coating is there to provide.
Common causes
- Entrapped air
- Incorrect application technique
- Porous substrate
- Excessive film thickness
- Inadequate application conditions
How can it be solved?
Identify the extent of defects, repair affected areas and reapply using the correct technique.
How can it be prevented?
Use proper application method and equipment, and follow recommended film thickness and conditions.
09Why does the coating sag or run?When the film flows downward
The coating flows downward, creating uneven surfaces. Sagging usually shows on vertical faces and leaves a film that is too thick in one place and too thin in another.
Common causes
- Excessive wet film thickness
- Incorrect spray technique
- Incorrect viscosity
- Poor application conditions
How can it be solved?
Allow the coating to cure, remove or smooth the affected area and recoat correctly.
How can it be prevented?
Control application technique and coating thickness. Apply the recommended amount per coat.
10Why does the coating discolour?Colour change, staining or uneven appearance
Discolouration appears as colour change, staining or uneven appearance across the coated surface.
Common causes
- Chemical exposure
- Heat or UV exposure
- Contaminants
- Reaction with substrate
- Incompatible coatings
How can it be solved?
Identify the cause, clean the surface and recoat with a suitable system if necessary.
How can it be prevented?
Select a coating suitable for the environment and exposure conditions.
11Why does the coating erode or wear away?When the film is worn off the surface
Erosion and wear show as coating worn away from the surface, usually where the asset is handled, walked on, or exposed to moving material.
Common causes
- Abrasion or mechanical impact
- Harsh operating conditions
- Chemical exposure
- Insufficient coating thickness
- Unsuitable coating type
How can it be solved?
Assess the extent of wear, remove damaged coating and reapply a more suitable and durable system.
How can it be prevented?
Use a coating system designed for the expected mechanical and chemical exposure, with adequate thickness and proper maintenance.
Identify the cause. Use the right solution. Apply correctly. Achieve longer lasting protection.
Protecting What Matters. Built to Last.