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Paint School2
Most common paint failuresMost common paint failures
• Holidays, too low DFT
• Sags and runs
• Orange peel
• Dry spraying
• Overspray
• Pinholes, popping
• Fish-eyes
• Wrinkling / lifting
• Sweating (Amine)
• Blushing
• Poor drying / curing
• Blisters
• Rust penetration
• Cracking
• Flaking
• Chalking
• Discolouration/bleeding
Paint School3
Sags and runsSags and runs
Appearance• Paint running or hanging like curtains on vertical surfaces
Caused by• Too high Wet film thickness
• Too much thinner added to the paint
• Airless spray gun too close to surface
Repair• Avoid above
• Use paint brush to smoothen or remove excessive paint
Paint School5
Orange peelOrange peel
• Paint surface is rough, like an orange peel
• Poor flow / levelling properties of the paint
(Paint too thick or too low temperature)
• Poor atomisation of the paint
• Too fast evaporation of the thinner
• Airless spray gun too close to surface
• Improve application technique
• Use correct thinner
• Grind surface and apply new paint
Appearance
Caused by
Repair
Paint School7
Dry sprayDry spray
• Porous, sandpaper like surface of the paint
• Poor atomisation of the paint
• Spray gun too far away from the object
• High air temperature and low relative humidity: Too fast evaporation of the solvents
• Strong wind during application
• Inorganic Zinc: Re-blast and apply new paint
• Physically drying paints: Apply thinner on the painted surface and apply a new coat
• Oxidativly drying paints: Remove loose dust and apply topcoat
• Two-pack paints: Remove loose dust, sandpaper to smooth surface, apply topcoat
AppearanceCaused by
Repair
Paint School8
Overspray Dry sprayOverspray Dry spray
• Blue top coat spray dust settling on welds etc.
• Overspray onto fresh paint
4226-584934-76
Paint School9
PinholesPinholes
Appearance
• Tiny holes through one or more coats, or even down to the substrate, as if perforated by a needle
Caused by
• Dry spraying
• Entrapped solvents or air
• Porosity of previous coat
• Incorrect application technique or viscosity of the paint
Repair
• Grind top layer of the paint
• Recoat
Paint School11
Pinholes / poppingPinholes / popping
Solvents or air try to evaporate through the upper part of the film, which has already nearly dried, leaving small bubbles /craters on the surface
• Very porous substrate (e.g. Zinc silicate primer)
• Entrapped solvents or air in the paint film
• Usually in connection with too high film thickness, too long application distance or too strong ventilation.
• Reduce film thickness or ventilation and adjust application technique (Tie coat / mist coat technique.
• Remove paint on painted surfaces and repaint
Appearance
Caused by
Repair
Paint School12
Pinholes / PoppingPinholes / Popping
• Porous substrate
• Too thick application
0807-4
0807-88
Paint School13
FisheyesFisheyes
Appearance
• Spots of paint on the surface with no wetting of the surface around the spots. Appearance of a fisheye.
Caused by
• Paint applied on oil, silicone or other contaminants
• Painted on incompatible paint (Glossy paint giving poor wetting)
Repair
• Grind top layer of the paint
• Recoat
Paint School14
Evaporation of solventsSilicon
FisheyesFisheyes
Wet topcoat
Primer
Blasted steel
Fisheye
Paint School15
WrinklingWrinkling
Appearance
• Small wrinkles through or partly through the paint film
Caused by
• Skin drying of the paint film, which is usually applied too thick
Repair
• Grind top layer of the paint
• Recoat
Paint School16
WrinklingWrinkling
• Paint applied too thick
• Skin drying
• Most common with alkyds
4847-0595
Paint School17
LiftingLifting
Appearance
• Small wrinkles through the paint film
Caused by
• Softening and raising or swelling of a previous coat by the application of an additional coat
• Normally when overcoating Alkyd
• Lifting often caused because the solvents in the new coat is too strong for the previous coat
Repair
• Remove the paint
• Recoat
Paint School19
Sweating and carbonisationSweating and carbonisation(Amine blooming)(Amine blooming)
Appearance
• Tacky and sweating film, often with white stains
Caused by
• High humidity, particularly on Epoxies during curing
• Poor ventilation
• The Amines react with CO2 and humidity and form Amine carbamate.
• Too low temperature
Repair
• Wash with warm water or thinner, using rags
Preventive measure: Induction time before application start
Paint School20
Amine blooming - SweatingAmine blooming - Sweating
• Steel painted with Epoxy
• Tacky surface
C22/2-17 C22/2-19
Tacky, shining surface
Tacky surface with white stains
Paint School21
Bloom and blushBloom and blush(Blushing)(Blushing)
Appearance• Surface looks milky
Caused by• Condensation on cold steel surfaces at high humidity
• Air pollution, sulphur dioxide (SO2) and ammonia forming ammonium sulphate on the paint film.
• “Fast “ thinners
Repair• Grind top layer of the paint
• Recoat
Paint School22
BlushingBlushingBloom / BlushBloom / Blush
Antifouling and top coat exposed to high humidity
4226-00660807-47
Paint School23
ISO 4628ISO 4628
• Evaluation of degradation of paint coatings
• Designation of intensity, quantity and size of common types of defect
Paint School24
ISO 4628 ISO 4628
Content of the StandardContent of the Standard
Part 1 General principles and rating schemes
Part 2 Designation of degree of blistering
Part 3 Designation of degree of rusting
Part 4 Designation of degree of cracking
Part 5 Designation of degree of flaking
Part 6 Designation of degree of chalking
The standard consists of six parts
Paint School25
ISO 4628 / 1ISO 4628 / 1General principles and rating schemesGeneral principles and rating schemes
Uniform deterioration. Rating scheme for designation the intensity of deterioration
consisting of a uniform change in the visual appearance of the paint coating.
Rating Intensity of change0
1
2
3
4
5
unchanged, i.e. no perceptible change
very slight, i.e. just perceptible change
slight i.e. clearly perceptible change
moderate, i.e. very clearly perceptible change
considerable, i.e. pronounced change
severe, i.e. intense change
Paint School26
ISO 4628 / 1ISO 4628 / 1General principles and rating schemesGeneral principles and rating schemes
Scattered defects. Rating scheme for designating the quantity of defects consisting
of discontinuities or other local imperfections of the paint coating.
RatingQuantity of defects
(relative to a test surface area of 1 to 2 dm²)
0
1
2
3
4
5
none, i.e. no detectable defects
very few, i.e. some just significant defects
few, i.e. small but significant amount of defects
Moderate, i.e. medium amount of defects
considerable, i.e. serious amount of defects
dense, i.e. dense pattern of defects
Paint School27
ISO 4628 / 1ISO 4628 / 1General principles and rating schemesGeneral principles and rating schemes
Rating scheme for designating the size (order of magnitude) of defects
Class Size of defect
0
1
2
3
4
5
not visible under 10 X magnification
only visible under magnification up to 10 X
just visible with normal corrected vision
clearly visible with normal corrected vision (up to 0,5 mm)
range 0,5 to 5 mm
larger than 5 mm
Paint School28
ISO 4628 / 1ISO 4628 / 1
Test reportTest reportThe test report shall contain at least the following information:
a) the type and identification of the product tested
b) a reference to this International Standard (ISO 4628/1)
c) the type of defect
d) the intensity of the defect (table 1) or,
e) the quantity of the defect (table 2)
f) the rating, if any, of the size of the defect in brackets preceded by the letter “S”.
Examples: cratering of top coat : 2 (S3)
whitening : 4
rivelling : 3 (S2)
Paint School29
ISO 4628 / 2ISO 4628 / 2Designation of degree of blisteringDesignation of degree of blistering
RatingRate the density and size of the blisters in a paint coating by means of the pictorial standards
NOTE - The photographic reference standards have been adopted from ASTM D 714-56The correlation between the ISO and the ASTM rating system is as shown in the table.
Table - Correlation between ISO and ASTM rating systems
Density Size
ASTM ISO ASTM ISONone
(less than few)
Few
Medium
Medium - Dense
Dense
0
1
2
3
4
5
(smaller than 8)
8
6
4
2
1
2
3
4
5
Paint School30
ISO 4628 / 2ISO 4628 / 2Designation of degree of blisteringDesignation of degree of blistering
Test reportThe test report shall contain at least the following information:
a) the type and identification of the product tested
b) a reference to this International Standard (ISO 462/2)
c) the numerical rating of the density of blistering
d) the numerical rating of the size of blistering.
for example: blisters 2 (S2)
Where a test piece exhibits blisters of varying size, quote as the size rating that of the largest blisters which are numerous enough to be typical of the test piece.
e) the date of the examination
Paint School31
ISO 4628 - 2 ISO 4628 - 2
Degree of blistering Degree of blistering
Density 2
Density 3
Density 4 Density 5
Blisters of size 5
Paint School32
Degree of blisteringDegree of blistering
• Osmotic blistering in WBT
• Two size and intensity of blisters
4934-00684226-0064
Paint School33
ISO 4628 / 3ISO 4628 / 3Designation of degree of rustingDesignation of degree of rusting
Rating
Designate the degree of rust formation by reference to the pictorial standards
Degree Area rusted %
Ri 0
Ri 1
Ri 2
Ri 3
Ri 4
Ri 5
0
0,05
0,5
1
8
40/50
Paint School34
Assessment of area ratio Assessment of area ratio for coating breakdown for coating breakdown
0.1 %
.
..
...
. ..
.
1.0 %
10 %
30 %
3.0 %
20 %
Paint School35
ISO 4628 / 3ISO 4628 / 3Designation of degree of rustingDesignation of degree of rusting
Test report:The test report shall contain at least the following information:
a) the type and identification of the product tested
b) a reference to this International Standard (ISO 4628/3)
c) the numerical rating of the rusted area
d) the numerical rating of the size of the rust spots, if desired,
for example: Rust: Ri 3 (S4) =
rusted area, as a percentage of rust, approximates standard 3, the sizes of the individual rust spots of the order of a few millimetres.
e) the date of the examination
Paint School37
ISO 4628 / 4ISO 4628 / 4Designation of degree of crackingDesignation of degree of cracking
Rating
Rate the quantity of cracking by reference to table 2 of ISO 4628/1 and using as examples figures 1 or 2, depending on the type of cracking
Rating scheme for the designation of the size of cracks
Class Size of cracks
012345
Not visible under 10 X magnificationOnly visible under magnification up to X 10Just visible with normal corrected visionClearly visible with normal corrected visionLarge cracks generally up to 1 mm wideVery large cracks generally more than 1 mm wide
Three main types of failure by cracking are to be distinguished:a) surface cracks which do not fully penetrate the top coatb) cracks which penetrate the top coat, the underlying coat(s) being substantially unaffected;c) cracks which penetrate the whole coating system
Paint School38
ISO 4628 / 4ISO 4628 / 4Designation of degree of crackingDesignation of degree of cracking
Test report:a) the type and identification of the product tested
b) a reference to this International Standard (ISO 4628/4)
c) the numerical rating of the quantity of cracking
d) the numerical rating of the size of cracking
e) the depth of cracking (a. b. or c), where possible,
for example: cracking 2 (S3) b
If necessary, the standard assessment may be amplified in words, for example “linear cracking”. The use of such comments shall, however, be avoided wherever possible
e) the date of the examination
Paint School39
ISO 4628 - 4 ISO 4628 - 4
Evaluation of crackingEvaluation of cracking
Quantity
1 2 3 4 5
Paint School40
ISO 4628 - 4 ISO 4628 - 4
Evaluation of cracking. Evaluation of cracking.
Quantity
1 2 3 4 5
Paint School41
Evaluation of crackingEvaluation of cracking
• Left: Thick old alkyd paint has been under stress
• Right: Too thick paint film (Cracking)
4934-0063 0807-30
Paint School42
ISO 4628 / 5ISO 4628 / 5Designation of degree of flakingDesignation of degree of flaking
Scale for the quantity of flaking
Class Flaked area012345
00,10,31315
Scale the average size of areas
Class Size of flaking0
12345
not visible under X magnification
up to 1 mmup to 3 mmup to 10 mmup to 30 mm
larger than 30 mm
The main types of failure by flaking are to be distinguished:
a) Top coats flaking from underlying coat;
b) Whole coating system flaking from substrate
Paint School43
ISO 4628 / 5ISO 4628 / 5Designation of degree of flakingDesignation of degree of flaking
Test reportThe test report shall contain at least the following information:
a) the type and identification of the product tested
b) a reference to this International Standard (ISO 4628/5)
c) the numerical rating of the quantity of flaking
d) the numerical rating of the size of flaking
e) the depth of flaking (a or b),
for example: flaking 3 (S2) a
Paint School44
ISO 4628 - 5ISO 4628 - 5 Evaluation of flaking. Evaluation of flaking.
Quantity
1 2 3 4 5
Paint School45
ISO 4628 - 5 ISO 4628 - 5
Evaluation of flaking. Evaluation of flaking.
Quantity
1 2 3 4 5
Paint School46
ISO 4628 / 6ISO 4628 / 6Evaluation of chalkingEvaluation of chalking
Part 6:
Rating of degree of chalking by tape method
Self-adhesive, transparent tape, of width
25 mm + 10 mm
– Chalking is removed by adhering to the tape
– Black or white background
– Comparing the amount of chalk on the tape with pictorial reference standard
Paint School47
ISO 4628 / 6ISO 4628 / 6Rating of degree of chalking by tape methodRating of degree of chalking by tape method
Test reporta) all details necessary for the identification of the product tested;
b) a reference to this International Standard (ISO 4628-6);
c) the type of weathering (artificial or natural) of the coating;
d) all details necessary for the identification of the adhesive tape used;
e) all details necessary for the identification of the substrate used as background for the adhesive tape;
f) the numerical rating of the degree of chalking;
g) any deviation from the procedure specified;
h) the date of the examination
Paint School48
ChalkingChalking
• Almost like dust on top of the coat
• The gloss will be reduced
Pigments and extenders exposed on the paint surface, due to
• Exposure to sun / UV light
• Degradation of the binder
• Weathering of the paint
• Insufficient mixing of the paint
• Grind and/or wash top layer of the paint
• Recoat
Appearance
Caused by
Repair
Paint School49
ISO 4628 - 6ISO 4628 - 6
ChalkingChalking
• Extreme case of chalking
• Due to degradation by exposure to sunlight
Paint School50
Standards relating methods for Standards relating methods for evaluation of degradation of coatings evaluation of degradation of coatings
Property Standard / Test method
BlisteringISO 4628 - 2, ASTM D 714DIN 53209, BS 3900 H2
Rust gradeISO 4628 - 3, ASTM D 610DIN 53210, BS 3900 H3
Cracking ISO 4628 - 4, ASTM D 661DIN ISO 4628, BS 3900 H4
Flaking ISO 4628 - 5, DIN ISO 4628BS 3900 H5
Chalking ISO 4628 - 6
Paint School51
BleedingBleeding
• Discolouration of a paint, particularly in topcoats
• Coloured ingredients in a previous coat or on the substrate is dissolved by solvents in the subsequent coat, e.g.
• Soluble pigments (Poor solvent resistance)
• Tar, Bitumen, etc.
• Surface contaminants (coloured)
• Re-blasting and re-application
Appearance
Caused by
Repair
Note:Note: Bleeding may continue through additional coats unless source is removed
Paint School53
DelaminationDelamination(Adhesion failure)(Adhesion failure)
Appearance• Loss of adhesion:
– Intercoat delamination: Between coats
– Substrate delamination : Between primer and substrate
Caused by• Primer not compatible with subsequent coat
• Contamination of substrate or between coats
• Recoating interval too long
• Blooming / sweating
Repair• Remove loose paint layer or down to substrate
• Recoat
Paint School54
Delamination (intercoat)Delamination (intercoat)
Intercoat delamination due to:
4226-364226-37
Too long recoating interval Condensation
Paint School55
Mud-crackingMud-cracking
Appearance
• Cracks occurring during the drying process of the paint
• Appearance of the surface of cracked mud
Caused by
• Particularly for inorganic Zinc applied at a too high film thickness
Repair
• Re-blast to Sa 2½ or grind off
• Apply the inorganic Zinc
Paint School56
Mud-crackingMud-cracking
Mud cracking of Zinc silicate
Paint applied at too high a thickness
4934-62