Glossary of Paint Defect Terms
Banding
This defect is found in spray applications where there is
heavy application of paint on the outside of the spray pattern
with little paint in the canter of the fan.
The cause can be:
- Too much air pressure
- Uneven lapping of the spray gun
- Having the gun too close to the job
The remedy may be found from:
- Use at correct air pressure
- Ensure that the overlap of each stroke is 50% over the
previous coat
- Hold gun at the correct distance from the job - about
15 cm for lacquers and 25 cm for enamels. To correct a coat
that has been applied, re-coat with double coat using thinner
that has been specifically recommended for the paint using
indicated solvent ratio and pressure, and ensuring that
the gun is held at the correct distance.
Bleeding
This is the migration of the color from a previous coat into
the freshly applied top coat. This defect usually occurs when
a light color is applied over a dark color, particularly reds
and maroons which are prepared by using organic pigments not
resistant to solvents or application over a surface contaminated
with bitumen where the solvents in the fresh paint dissolve
the bitumen.
The remedy is:
- Use a bleed sealer before application of the light color
- Wash the surface with mineral turps if it is contaminated
with bitumen.
Blistering
This defect is the appearance of irregular blisters on the
paint finish.
This defect can be caused by:
- Not correctly cleaning substrate
- Contamination of the brush, air gun, line etc.
- Using wrong thinner or incorrect amount of thinners
- Old paint surface
- Excess film thickness
- In timber finishes, not allowing the solvent, particularly
paint removers , to evaporate before repainting
This defect may be overcome by:
- Cleaning all surfaces free of grease and allowing the
solvent to evaporate.
- Using recommended thinner at correct ratio.
- In spray applications, inspect so that water does not
build up in the traps, especially in humid weather.
- Check that the new paint is compatible with the old surface.
- Do not apply paint films too quickly and allow solvents
to evaporate before re-coating.
Blooming
This defect gives a bloom or white deposit, like the bloom
on a grape or plum, after the paint has dried. The cause is
the rising of soluble fractions of the pigment rising to the
surface on the paint's drying. The remedy for spray paints
is to rub the surface down.
Blushing
This is a white deposit appearing on the surface of lacquer
films only. The defect is caused by painting with lacquers
in high humidity conditions where the water contained in the
air condenses on the paint film The remedy is not to paint
in humid conditions or to add a strong, active solvent that
may stop the blushing.
Bronzing
This is a defect that was often observed on cars painted
red or blue where after a period of time a characteristic
red tone developed on the paint surface. The cause was older
types of pigments like phthalocyanine or Prussian blues. The
defect is not common with the pigments available today.
Chalking
Chalking is the powdery deposit on the surface of the paint
which dulls the gloss and appears after exposure. This defect
is usually associated with long exposures to sunlight and
is a natural degradation of the paint film. Some combinations
and types of pigments and resins show more pronounced chalking
than others.
Checking
Checking is the appearance of wide splits with round edges
that occur in the top coat. The cause is usually due to the
surface not being clean (could be old paint) or too high a
film build or the materials not being mixed properly. The
remedy is to remove the old paint, cleaning the surface and
mixing the paint ingredients properly.
Cracking or Crazing
This defect is a series of irregular cracks in the surface
of the paint.
The cause of this defect can be:
- Application of the top coat before the previous coat is
dried
- Too thick of a top coat
- Impurities on the surface or the effect of impurities
on the applied coat.
The remedy is the let the intermediate coats dry before the
top coat is applied, clean the surface well, remove the previous
coat or ensure that the top coat is not applied too thickly.
Dirt Retention
This is the deposition of dirt and dust on the paint film.
For certain types of paint, the dirt may become entrained
into the surface. The paints that resist dirt retention are
high-gloss enamels while the low gloss latexes are the most
susceptible to this defect.
Fading
Fading is the decrease in the intensity of the color after
exposure. It should be tested for after removal of any chalking
that may have occurred as this will tend to mask the actual
fade of the pigment. In general organic pigments, especially
those of low cost, will fade more than pigments that are inorganic.
More expensive coatings especially prepared for exterior exposure
will resist fading more than less expensive paints.
Fish Eye
This defect is indicated by small round imperfections in
the top coat. The defect is caused by traces of silicone or
oil on the surface prior to painting. The remedy is to thoroughly
clean the surface and if spray painting, to ensure that there
is an oil filter on the air line.
Flaking
Flaking is the lifting of small-to-large sections of the
paint and is due to poor adhesion and to the brittleness of
the paint. The causes can be varied, for example the defect
could be caused by efflorescence or the migration of soluble
salts to the paint-media interface which can cause the paint
to be forced off the surface. The paint may react with moisture
and any traces of alkali to decompose the paint - this is
called saponification. It may be due to failure to remove
millscale from the steel before painting.
Floatation and Flooding
Floatation or floating occurs when a paint has been incorrectly
formulated with two or more different colored pigments when
one of the pigments floats to the surface giving different
differences. On close examination the surface appears mottled
with regular shaped cells.
Flooding is similar to floatation in that one of the pigments
migrates to the surface when the paint is produced using two
pigments with different densities.
These defects are corrected mainly by better paint formulation.
Gassing
This is the formation of a gas, usually by hydrogen, by the
reaction of reactive pigments, like Zinc and Aluminum, with
acidic materials in the resin. It can be overcome by better
formulation or packaging the paint separate from the pigment
and mixing the ingredients prior to application.
Mould
The growth of mould on a paint film causes severe discoloration.
Mould is a plant growth that requires moisture, the presence
of food and the correct temperature for growth. The defect
can occur on most types of paint but is most prevalent in
bathrooms, kitchens and exterior walls that are in shady positions.
The paints that are most susceptible are soft oil-based paints
or varnishes and emulsions, especially if they are low gloss
where dirt can be trapped in the film.
Often the mould growth can be killed and color removed by
washing with dilute sodium hypochlorite solution taking due
care as this preparation is alkaline. Safety glasses and gloves
have to be worn. Before repainting, susceptible surfaces should
be prepared with anti-mould preparations, like sodium pentachlorophenate
and by using either paints prepared with mould inhibiting
pigments, like Zinc oxide, or by using high gloss finishes.
In extreme cases it may be necessary to remove the high humidity
in the room by using exhaust fans.
Orange Peel
This defect gives the paint finish the rough appearance similar
to the outside of an orange. The defect is found in spray
painting and is generally due to having the wrong solvent.
It can also be due to an incorrectly adjusted spray gun.
The solution is to use the manufacturers recommended thinner
and to adjust and use the gun correctly.
Peeling
Peeling is simply another type of flaking where the amount
of paint film removed is greater.
Pinholing
The defect is the appearance of small holes in dried paint
film. The problem is most probably caused by too thick a coat
trapping solvents into the film, or by air bubbles. The defect
may be due to not cleaning the surface before painting, using
the wrong solvents in spray painting or incorrect air pressure.
The problem can be solved by addressing the above causes.
Poor Flow
Poor flow can manifest itself in two ways: if the paint is
too thick and will not flow out this will show up as a rough
surface or orange peel where the surface resembles the skin
of an orange; if the paint flows too much the result will
be runs, sags and wave formation. This defect is remedied
by proper formulation and when thinning the paint to use the
right solvent and the correct amount.
Poor Hiding or Lack of Opacity
Opacity is the ability of a paint film, when applied to a
given surface, to hide or obliterate the surface or the undercoat.
Poor hiding power can be due to too thin a coat being applied
or to the formulation using a poor quality pigment.
Runs and Sags
As the name suggests this is the formulation of runs or sages
on the finished paint film.
The defect can be caused by a number of things:
- Too thick of a film.
- Too much thinners.
- Not allowing the first coat to dry before applying the
top coat.
Settling
This is the separation of the pigments and occurs to a certain
extent in all paints. It becomes a serious defect when the
pigment is difficult to reincorporate into the paint by stirring.
The defect occurs due to the high densities of some pigments
and can be accelerated by a drop in viscosity, the paint being
stored at high ambient temperatures or by being subjected
to vibration for example on long transportation by rail.
The control of settling lies in selection of suitable pigments
and the addition of additives that increase the viscosity
of the paint.
Slow Drying
Slow drying occurs when the paint remains tacky for an extended
period of time. This will result in the film picking up insects
or dirt before it is hard and will make repainting difficult.
The main causes are:
- Too thick of an application of the paint when using air-drying
paints. As these paints require oxygen to penetrate the
film to produce dying, if the film is too thick oxygen will
not penetrate.
- The viscosity of the paint is too high for the application.
This can occur in cold weather and can be overcome by reducing
the viscosity with the recommended thinners for the paint.
- The paint was applied at too cold a temperature. This
will cause the chemical reaction that takes place to cause
the film to cure slowly.
- High humidity due to rain or the like will reduce the
evaporation of the solvent, the first step in drying.
- The surface to which the paint is applied is not clean
and has traces of wax or paint removed on it.
- The coat to which the paint is being applied has not dried
when the next coat is applied.
Staining
Contamination of many surfaces with water, soot, smoke, tannins
and tobacco can result in color coming through the paint surface
to cause stains. Stains caused by water will leave a tide
mark and after drying, the paint around the stain can be removed
and the surface repainted. If the surface may become damp
again, remove the source of the water or paint with chlorinated
rubber or a hard varnish. Patches of soot or smoke should
be removed before coating. Use of an insulating paint before
the final coat can help. Nicotine should be removed with an
alkaline cleaner (bleach) before coating. Remember to wash
off all the alkali before attempting to paint.
Viscosity Drop
Low viscosities may be simply due to incomplete stirring
or the addition of too much solvent. The viscosity may decrease
on standing in water-borne paints due to enzymic attack on
the thickeners used. Modern latex paints use thickeners that
are not readily attacked by bacteria. Changes in the orientation
of the pigments (for example partial flocculation) may reduce
the viscosity.
Wrinkling, Webbing, Frosting and Gas Checking
Wrinkling is the development of wrinkles in the paint film
as it dries, usually due to the formation of a skin. Defects
similar to wrinkling are webbing, frosting and gas checking.
Webbing is the development of wrinkles, usually in a well
defined pattern and if it occurs in an oven it is called gas
checking. Frosting is the formation a haze which is due to
fine wrinkles and it occurs in gas fired drying ovens.
The causes can be:
- Due to the paint's being applied too thick, especially
with high oil-length alkyds, varnishes with wood oil and
too much cobalt drier, enamels based on alkyd or phenolic
resins with drying oils and black enamels containing bitumen.
- Stoving paints containing bitumen.
- Frosting may be due to the products combustion in the
oven reacting with the surface of the film or may be due
to high humidity.
- Too much cobalt drier.
Sometimes the wrinkle pattern may be induced into the paint
to produce films that will hide surface defects.
Another type of defected related to wrinkling are crocodiling
or alligatoring where the wrinkle pattern resembles the hide
of one of these reptiles.
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