Page 177 - CW E-Magazine (24-6-2025)

Special Report

Prevention methods in the paint film takes place in a pattern reasons such as: incorrect pigmenta-
Use correct coating systems, appli- resembling to a crow’s foot as illustrated tion; use of non-light-stable organic
cation techniques, and ensure proper in Figure-19. pigments; atmospheric contamination;
dry-film thicknesses. Alternatively, and/or porous substrate. Figure-21
use a more flexible coating system. Prevention methods shows discoloration/fading of paint
Apply a thinner coat of paint, add colour when exposed to sunlight/
cratering slower-drying thinners, and check that weather accompanied by loss of gloss
Cratering is caused by trapped air application and drying conditions are tending to accelerate in presence of
or solvent bubbles that have burst, correct for the paint system used. moisture.

delamination Prevention methods
If compatible paint materials have Use correct coating systems that
been used, delamination defects are resist ultraviolet light and fading. Use
a coating with light-stable pigments.

Flaking
Flaking takes place due to incor-

Fig. 18: cratering
leaving small craters as the coating
dries. The coating has insufficient time
to flow into a uniform film. Figure-18
shows the formation of small bowl- Fig. 20: delamination
shaped depressions in the paint film generally related to poor surface prepa-
caused by cratering failure of a ration and application defects, such as
coating. contamination between coats, exceed-
ing overcoat times, or application to a Fig. 22: Flaking
Prevention methods glossy surface. Figure-20 depicts loss rect paint system used. Either no or
Improve spray technique, apply a of adhesion between coats of paint due an incorrect pretreatment is used for
mist coat, and avoid air entrainment to delamination. certain substrates, for example, non-
during mixing. Add thinners as recom- ferrous or galvanized. Flaking may
mended by the paint supplier. Prevention methods also be caused due to poor application.
Ensure no contamination occurs It may also be attributed to differential
crowsfooting between paint coats. Follow the recom- expansion and contraction of paint and
Usually takes place due to the sur- mended over-coating intervals. Lightly substrate, for example, wood. It can be
face drying rapidly to form a skin, abrade and clean glossy surfaces the result of aging of the paint system
between coats. also (Figure-22).

Fading Prevention methods
Fading may be caused due to the Correct coating system and pre-
treatment should be used.

Grinning
Caused due to low film thickness of
topcoat and poor opacity and covering
power of topcoat. Grinning of coating
Fig. 19: crow’s footing may also be caused due to strong colour
which then wrinkles as solvent slowly of primer/undercoats, etc. The underly-
evaporates from the soft underlying ing surface is visible through the paint
paint. Development of small wrinkles Fig. 21: Fading film due to inadequate hiding power of

Chemical Weekly June 24, 2025 177

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