chapter 14 coatings failurs Flashcards
the mechanism of chalking is essentially one in which the coating _______ tends to gradually _______, leaving the surface covered with pigments that had been held on the surface by the ________.
binder
disintegrate
binder
______ or ______ of a coating is due to the exposure of a coating to the ________ rays of the sun and the action of the __________ on the organic binder.
powdering
chalking
actinic
radiation
_______ have a positive influence on chalking, as they tend to reduce the chalking by _______ the resin from the sun’s rays
pigments
shielding
Identify an ASTM standard that provides a method of determining the degree of chalking
ASTM standard D4214
_______ is essentially a wearing away of the coating surface in a _______ manner similar to the chalking mechanism.
Erosion
gradual
_______ is small breaks in a coating surface that forms as a coating ages and does not ______ the full depth of the coating.
Checking
penetrate
_______ is the shrinkage of the surface while at the same time the _____ of the coating does not change in the same way.
Alligatoring
body
___________ results from stresses on the _______, while cracking is caused by stresses ______ the film and ______ the film and the substrate.
checking
surface
throughtou
between
Cracking occurs as a coating ages: as it is subject to _____ and _____, ____ and _____, _____, and _____ of moisture, etc.
expansion and contraction
wetting and drying
absorption and desorption
Reinforcing pigments, which are _____ or _______, aid materially in reinforcing the coating against cracking action.
Fibrous or acicular
ASTM Standard _______ can be used to evaluate extent of cracking.
D661-81
___ ______ occurs when highly filled coatings area applied rather heavily.
Mud cracking
______ is the result of the ______ of a coating where the _____ of the coating expands more rapidly during the drying period than the ______ of the coating.
Wrinkling
swelling
surface
body
Some driers are used to speed the _____ cure and others are used as ______-______ materials
Surface
through- drying
_____ materials are examples of surface driers; _____ and _____ compounds are classified as through driers.
Cobalt
zinc and lead
Poly-amide curing agents are susceptible to biological failure, while _____ ____ curing agents have excellent resistance to sewage conditions.
Amine type
Fungus growth can be largely eliminated by the use of _____ _____ as part of the pigmentation, along with the addition of _____ , _____ or a combination of all three.
Zinc Oxide
Fungicides
Bactericides
Inorganic zinc coatings are highly filled with metallic zinc, and the _____ to binder ration is very high, so when drying is ____, fine surface ____ can occur.
pigment
rapid
checking
Chalking remedy
coating formulated with radiation resistant resins (acrylic) and non catalytic, non chalking pigments.
Alligatoring remedy
Apply thin coats, dry thoruoughly before additional coats, never apply hard top coats (epoxy) over soft under coat (asphalt).
Mud Cracking remedy
use coatings with strong adhesions, apply under proper drying conditions, prevent sags, puddles, or areas of excess thickness.
Biological failure remedy
select oil-based coating which contain fungicides or bactericides.
Wrinkling
choose coatings with even, thorough drying, charctristics
apply evenly avoid excess thickness.
pinpoint rusting remedy
apply maintenance coat at first sign of failure.
remove coating and reapply more satisfactory zinc coating.
erosion remedy
select chalk resistant coating with good flow out to a smooth film
three types of contaminants in steel after blasting
rusting
chlorides
sulfides
previously used steel failure
retention of minute amounts of corrosion product or contaminant along grain boundaries of the steel.
galvanized steel failure
formation of zinc salts (oxides, sulfide, zinc soap)
copper failure
smooth copper oxide surface. No physical adhesions
wood failure
expansion and contraction due to humidity soft porous grain
concrete failure
chemical reactivity and moisture content
coating failures are more probable when _____ are used than when the same coating is applied over a _____ abrasive blasted surface.
inhibitors
dry
retained solvents may cause ______ and ___ adhesion to the substrate because the underlying coating is ____ and the ___ ___ are close to the substrate.
blistering and low
porous
retained solvents
regardless of their size and description, _____ are essentially discontinuity in a coating.
Holidays
______ is generally the result of poor gun adjustment, or application of the coating at too ____ a distnce from the surface, and not applying an even _____ film to the surface.
over-spray
great
wet
For the most part, ______ result from ______ application of a coating, with ____ being blown into the surface during the application.
pinholes
heavy
air
cratering (or ________ or ______) may be either an ______ problem, a _____ problem, or _______.
bug-eying or crawling
application
material
or both
Much catering is due to _______ on the surface or that falls into the wet coating.
contamination
runs, sags, and curtains failures
lack of care in application
Brush mark failure
pooor workmanship
overspray failure
uneven spray passes with gun too far from the surface
pinhole failures
spray gun to close to surface with air bubbles being forced into coating
holidays failure
poor, inconsistent application
cratering failure
improper solvent mixture
two types of blisters
coating separating from substrate or
between coats
Where there is solvent retention and the coated surface _____ in temperature, the solvent itself may create a sufficient _____ pressure to cause blisters to form in the coating.
changes
vapor
cathodic protection blisters in coatings are caused by _____ gas being formed on the metal underneath the coating is sufficient volume so the the _____ ____ pressure pushes the coating off the surface.
hydrogen
hydrogen vapor
peeling can be caused by _____ surface preparation, _____ between coats, or when the coating thickness is too _______.
poor
contamination
great
_______ is much like peeling except that the flaked coating is usually _____ and _____ and tends to pull itself away from the substrate.
Flaking
hard and brittle
Inter-coat _________ occurs most often where repair or maintenance coatings are being applied over existing coatings that are _____, have ______ embedded in the surface, or have oxidized or cured to the point of complete _______ and ________.
delamination
chalky
dirt
insolubility and impenetrability
When coal tar epoxy coatings are exposed to ______, that will catylyze the curing of the surface to the point where additional coats will not ______ ______.
sunlight
adhere properly
__________ of a coating is the action of rust under the coating, usually forming around a small _____ in the coating.
undercutting
break
A coating applied over ____ ____ is susceptible to undercutting, since once a break in the coating occurs: corrosion can begin between the ____-____ _____ and the steel
Mil scale
mil scale surface
Reverse impact is ____ ____ difficult for a coating to resist than _____ _____ .
much more
direct impact
Most coatings are _____ for faying surfaces because of the fact that the coefficient of friction is not _____ for the bonding of the joint.
unsuitable
sufficient
