The document defines and categorizes various coating defects that can occur, including those related to surface preparation, application, and the coating film itself. It describes 13 common defects - blistering, bubbling, checking, cracking, corrosion, edge/corner failure, peeling/flaking/delaminating - and discusses their causes. The document is intended for internal use by AkzoNobel Protective Coatings to understand and address coating defects.

1. Coating Defects
For internal use only – not to be circulated outside AkzoNobel Protective Coatings

2. Contents
• Definition of Coating Defects
• Types of Coating Defects
• Causes of Coating Defects
• Specific Defects
• Surface Preparation
• Application
• In Service
• Inherent
• Film Defects
For internal use only – not to be circulated outside AkzoNobel Protective Coatings

3. Definition & Types of Coating Defects
Flaw that spoils the required appearance and specified
performance of a painted surface
Types of Defects
• Blistering
• Bleeding
• Poor Coverage
• Loss of Gloss
• Loss of Adhesion
• Wrinkling
• Spray dust/Overspray
• Rash Rusting
• Pinholes
• Cratering
• Chalking
• Runs
• Orange Peel
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4. Causes of Coating Defects
 Poor surface preparation
• Surface contamination
• Surface profile
 Poor application
• Mixing (1-pack & 2-pack)
• Use of brush & roller (low dft per coat)
• Use of spraying (low or high dft per coat)
For internal use only – not to be circulated outside AkzoNobel Protective Coatings

5. Causes of Coating Defects
 Incorrect Paint Systems
• eg 2-pack over 1-pack systems
• Incorrect system for the environment
• eg Anticorrosive or Antifouling performance needs
 Poor Engineering Design
• Inherent design defects (eg stitch welding)
 Poor Quality of Paints
• Product/batch related problems
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6. Specific Defects – Surface Preparation
1) Blast Profile Effects
• Profile too small gives poor key for adhesion
• Profile too large means peaks may protrude through
the paint film as paint flows away from peaks.
Steel Profile Paint barely covering high
peaks of blast profile.
Applied Coating
Low film thickness of paint over steel with large blast profile
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7. Specific Defects – Surface Preparation
2) Cissing
• Due to contamination of the surface, (eg where paint
can not wet the surface fully) or in the paint.
• The wet paint appears to retract from some areas,
and this is often associated with oil or other
contamination of the surface
3) Millscale effects
• Detachment & Galvanic Corrosion.
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8. Specific Defects – Surface Preparation
4) Welding Issues
• Painting over weld flux residues can cause problems
as it is hygroscopic (absorbs water and then dissolves
in it) and corrosion will break through the coating at
these points
• Paint applied over weld spatter will show early
breakdown, due to shrinkage stress in the coating.
For internal use only – not to be circulated outside AkzoNobel Protective Coatings

9. Specific Defects – Application
1) Blooming
• surface effect if amine & amine-adduct cured
epoxies contact with water before full cure.
• unreacted curing agent takes up moisture.
• not detrimental to film performance but must be
removed (solvent wiping) before painting.
2) Blushing
• White surface film soon after application at high
humidity due to condensation in the film.
For internal use only – not to be circulated outside AkzoNobel Protective Coatings

10. Specific Defects – Application
3) Dry Spray
• To coalesce and form a continuous film, paint must
still be fluid when it reaches the surface.
Target steel
(panel, ship etc)
Spray
Gun
Wet Paint merging
from spray tip.
Evapouration of solvent from
atomised droplets before they
can reach the surface..
For internal use only – not to be circulated outside AkzoNobel Protective Coatings

11. Specific Defects – Application
4) Lapping
• Brush strokes & spray pass stay visible after drying.
• Most obvious on paints with fast solvents on hot
steel - especially if aluminium pigmented.
• Adding slow solvents can help - or end passes at
welds.
5) Pin holing
• Circular pits which appear to be free of paint.
• Bubbles break at a stage where the coating has
already dried too much for it to flow and repair the
broken surface.
For internal use only – not to be circulated outside AkzoNobel Protective Coatings

12. Specific Defects – Application
6) Sagging & Curtaining
Weight of paint on a surface is too much for the flow
properties of the paint to support, due to:-
a) Too high thickness applied.
b) Too much thinner added to the paint.
c) Not enough thixotropy for expected wft.
d) Temperature too low / solvent too slow.
7) Wrinkling
Common on alkyds at high dft, where surface drying
of the film occurs while the under portion of the film
remains soft for a longer time
For internal use only – not to be circulated outside AkzoNobel Protective Coatings

13. Specific Defects – Application
Sagging & Curtaining
Under the
effect of
gravity.
Coating Steel
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14. Specific Defects – Application
Sagging & Runs
‘Downward movement of paint on vertical surfaces during
drying process.’
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15. Specific Defects – Application
Wrinkling
‘A rough crinkled
surface caused by a
drying interference
forming a wrinkled
skin’
Cause
•Applying the paint too thickly
•Over coating an insufficiently cured primer
•Painting during extreme hot or cool / damp conditions
forcing skin to form rather than cure to occur
Remedial Action
•Remove wrinkled layers by sanding / scraping
•Patch prime and finish allowing adequate cure in
between coats
For internal use only – not to be circulated outside AkzoNobel Protective Coatings

16. Specific Defects – In Service
1) Mechanical Damage
• Scratching etc is an unavoidable fact of life, but
certain precautions can be taken in terms of handling
times and the coating specified for a particular use.
2) Sulphide Discoloration on Surface
• The reaction of H2S with lead pigments and driers
• May be uniform or spotted (where water droplets
have absorbed sulphide from the air)
• Not, generally, a serious problem for long-term
performance of the coating, but can be unsightly.
For internal use only – not to be circulated outside AkzoNobel Protective Coatings

17. Specific Defects – Inherent
1) Bleeding
• some pigments are solvent soluble
• Tar & Bituminous coatings will bleed through if next
coat has strong solvents
2) Chalking
• Common for epoxies, as UV degradation of the resin
at the surface causes breakdown and the release of
pigment particles.
• It is a surface effect only, and not associated with a
true failure. However, surface dust must be washed off
before applying further coats.
For internal use only – not to be circulated outside AkzoNobel Protective Coatings

18. Specific Defects – Inherent
Chalking
UV Light
Long
Exposure
UV Light
Most of the coating
is not affected
The upper layer
is broken down
by UV light
For internal use only – not to be circulated outside AkzoNobel Protective Coatings

19. Specific Defects – Inherent
3) Reduced inhibiting effect on weathering
• Primers are formulated to protect steel from
corroding, and topcoats are to protect the primers
from weathering.
• If primer is exposed, soluble salts will be leached
away.
• In red oxide primers, effect might not be obvious,
but when they are overcoated, rapid breakdown
occurs.
For internal use only – not to be circulated outside AkzoNobel Protective Coatings

20. Surface Discoloration
‘Coating surface has a different appearance from that
when it was originally applied.’
For internal use only – not to be circulated outside AkzoNobel Protective Coatings

21. Specific Defects – Film Defects
1) Blistering
Caused by:-
• painting over moisture
• painting over soluble salts
• solvent entrapment
• coating permeability to gas
• excessive Cathodic Protection
• painting over porous surfaces
For internal use only – not to be circulated outside AkzoNobel Protective Coatings

22. Specific Defects – Film Defects
Blistering
‘Formation of gas or fluid-filled voids with the coating.’
Liquid / gas exerts a pressure on coating greater than
adhesion strength causing localised detachment. Coating
stretches to form hemispherical blister(s). Once internal
pressure exceeds coating strength, the coating will
rupture leading to holiday in coating.
For internal use only – not to be circulated outside AkzoNobel Protective Coatings

23. Specific Defects – Film Defects
2) Bubbling
Caused by:-
• Painting over porous substrates (eg Zinc Silicate)
and displacement of air - Mist Coats.
• Wrong application method - some enamels bubble if
applied by roller if warm and windy.
• Applying low solids coatings at high dft where
surface dries while solvent is still trying to escape,
resulting in a mass of tiny bubbles.
For internal use only – not to be circulated outside AkzoNobel Protective Coatings

24. Specific Defects – Film Defects
3) Checking
• Surface cracking which does not penetrate right
through the topcoat - and may need a lens to see it.
• Caused by contraction of the topcoat of paint, and
common in dark chlorinated rubbers in hot climates.
For internal use only – not to be circulated outside AkzoNobel Protective Coatings

25. Specific Defects – Film Defects
4) Cracking
• Fracture of at least the topcoat of paint with ageing,
and occurs when the substrate and coating expand
and contract at different rates.
• As paint films age, they become harder and less
flexible and so “Something has to give”.
• Thin films tend to crack less than thick films.
For internal use only – not to be circulated outside AkzoNobel Protective Coatings

26. Specific Defects – Film Defects
Cracking
Steel and coating
layers expand and
contract at different
rates
Many
temperature
cycles
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27. Different Types of Cracking
Hairline – fine surface cracks that occur erratically and at random
Checking – As above, but give a uniform pattern
Crazing – Similar to checking, but go deeper and are broader
Cracking – Breakdown penetrates to substrate, corrosion and
detachment
Mud Cracks – penetrate to substrate and form uniform pattern.
(Zn Silicates)
Cracking Hairline Mud Cracking
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28. Specific Defects – Film Defects
5) Corrosion (Rash Rusting)
Caused by:-
• low film thickness
• poor surface preparation
• Wrong selection of coating system
For internal use only – not to be circulated outside AkzoNobel Protective Coatings

29. Specific Defects – Film Defects
Liquid Paint
6) Edge & Corner failure
• Liquids draw away from sharp points.
• Use Stripe Coating to can overcome this.
For internal use only – not to be circulated outside AkzoNobel Protective Coatings

30. Specific Defects – Film Defects
7) Peeling, Flaking & Delaminating (Detaching)
• Reporting “there is serious detachment” does not
give much information - or help to provide a solution.
• Peeling - when paint curls off a substrate.
• Flaking - when paint detaches in flakes.
• Delaminating - intercoat adhesion failure.
For internal use only – not to be circulated outside AkzoNobel Protective Coatings

31. Specific Defects – Film Defects
Note Area of weakness
due to internal stresses
Multiple coats representing
frequent applications
For internal use only – not to be circulated outside AkzoNobel Protective Coatings

32. Specific Defects – Film Defects
Detachment
‘Delamination of coatings or entire scheme from substrate’
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33. Specific Defects – Film Defects
Detachment
Detachment due to surface contamination
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34. Specific Defects – Film Defects
Coatings Detachment Inspection
Coat #2
Coat #1
Steel
Flake
Front
Flake
Back
Left behind
Flake
Front
Flake
Back
Left behind
Flake
Front
Flake
Back
Left behind
Detachment from Steel Substrate
Due to surface contamination,
application beyond pot-life etc
Delamination
Due to surface contamination,
coating incompatibility etc
Cohesive failure
Weakness within a coat due to
solvent entrapment etc
For internal use only – not to be circulated outside AkzoNobel Protective Coatings

35. Final Thoughts & Suggestions
• Zinc-rich coatings such as epoxy zinc and zinc
silicates have quite a number of advantages where top
coating is to be performed, as these do not suffer most
of the problems described.
• Do not allow subcontractors to amend or adjust any
surface preparation or coating system specified,
however well-meaning their intentions may be.
• It is the usual practices that have been followed for
years that are as wrong now as they were then.
• Always seek professional and reliable advice while
preparing coating specifications.
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