MIL-HDBK-1110
11.4.2
Film Failures. The following paragraphs further
describe the film defects chosen in the initial decision.
11.4.2.1 Crawling. Crawling, sometimes called bug eyeing or
fish eyeing, occurs during coating application, frequently on
contaminated surfaces. It can usually be detected at the time of
application. The smooth, oval shapes resembling eyes are
characteristic of crawling.
11.4.2.2 Alligatoring. The characteristic checkered pattern of
cracked coating will identify alligatoring. The coating is quite
inflexible and cannot expand and contract with the substrate. It
is a special form of cracking or checking.
11.4.2.3 Intercoat Delamination. Intercoat delamination is
simply the peeling of a stressed coat from an undercoat to which
it is poorly bonded. It may occur in a variety of situations,
but occurs frequently when a chemically curing coating such as an
epoxy or a urethane has cured too hard to permit good bonding of
a topcoat. It may also occur when coating a contaminated
surface.
11.4.2.4 Intercoat Blistering. Intercoat blistering in a
storage tank or other enclosed area is likely due to solvent
entrapment. In water tanks or other areas exposed to water, the
trapped solvent will cause water to be pulled into the blister.
If the blisters are large, unbroken, and filled with water, it is
sometimes possible to smell the retained solvent after breaking
them. Intercoat blistering may lead to intercoat delamination.
11.4.2.5 Pinpoint Rusting. Pinpoint rusting is frequently
caused by applying a thin coating over a high profile steel
surface. A thin coating can be verified using a magnetic
thickness gage. It may also occur when steel is coated with a
porous latex coating system. Pinpoint rusting may initiate
corrosion undercutting of the coating.
11.4.2.6 Cracking. Cracking is the splitting of a stressed film
in either a relatively straight or curved line to an undercoat or
the structural substrate. Cracking may occur from rapidly curing
coatings such as amine-cured epoxies. Mudcracking is a more
severe condition caused by rapid drying, particularly by heavily
pigmented coatings such as inorganic zincs. It also occurs with
latex coatings applied too thickly on hot days. On wood, too
thick or too inflexible a film (usually a buildup of many layers)
can cause cracking perpendicular to the grain of the wood.
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