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FILM
THICKNESS -
Film thickness
measurement plays an essential part in the use and testing of paints and coating
materials. The film thickness is a decisive factor in determining appearance, protective
qualities and durability. Film thickness in coatings can have a big impact on cost
and quality. Measurement of film thickness should be a routine event for all coaters.
A film,
which is too thin, will afford inadequate protection and reduced hiding power. For
this reason, technical
specifications stipulate minimum film thickness and regular controls must be carried
out to ensure that these values are consistent.
On the
other hand, an excessively thick film is the result of using too much coating material,
causing costs to increase accordingly. Furthermore, thicker coatings do not always
mean an improvement in properties- for example; they have an adverse affect on drying
time.
The physical
and mechanical properties of a coating are directly dependent on the film thickness.
If meaningful testing is to be conducted, the film thickness must therefore be uniform.
The correct
gauge to use depends on the thickness range of the coating, the shape and type of
substrate, the cost of the gauge, and how critical it is to get an accurate measurement.
DRY FILM
THICKNESS -
Dry Film
Thickness is the thickness of an applied coating when dry; expressed in mils.
For the
protection of any surface, an adequate dry film thickness of paint must be applied.
If more than the recommended film thickness is applied, the life of the protective
coating will normally be extended. Conversely, if less than recommended thickness
is applied, the durability and performance of the system will be suspect.
The actual
dry film thickness recommended for a particular surface will depend upon the paint
system and the surface to be coated. Factors that control the coverage of the paint
are wastage, the porosity and roughness of the surface. The latter factor, the type
of surface, must always be taken into account when calculating the volume of paint
to cover a given area.
The calculation
of the theoretical coverage or spreading rate of paint is determined from the volume
solids. The volume solid is defined as the percentage of solids, expressed in volume,
in paint.
Dry film
thickness is measured using mechanical or electronic dry film thickness gauges to
ensure adequate coverage according to specifications. It may be necessary to test
coating adhesion.
Dry film
thickness gauge is an instrument for measuring the dry film thickness of a coating.
Mechanical film thickness gauges provide a number of advantages:
· Handy, portable,
and simple to operate even by unskilled personnel, sturdy construction, direct reading.
· Measurements
can be carried out on any surface. Since the system functions completely mechanically,
substrates of glass, wood, metal or plastic are permissible.
· In comparison
to other systems, mechanical film thickness gauges are favorably priced.
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