06 coating failures

Paint School1

Coating failuresCoating failures

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 School4

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Sags and runsSags and runs

Too thick application of antifouling

4226-48

4934-82

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 School6

Orange peelOrange peel

Poor flow / levelling properties of the paint

1183-0026

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 School10

PinholesPinholes

• Paint applied to a porous substrate

4934-67

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


• 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


• 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 School18

LiftingLifting

• Wrinkled and tacky surface

• Coatings not compatible

4934-0066

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


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


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:



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:



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.


Paint School36

ISO 4628 - 3 ISO 4628 - 3

Degree of rusting Degree of rusting

Ri 5

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


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


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:



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 School52

BleedingBleeding

Tar epoxy bleeding through yellow vinyl coat

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

Paint School57

Cracking / AlligatoringCracking / Alligatoring

Soft coat under a hard coat

0807-194934-61

06 coating failures

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