Technical data

a. Allow materials to come to room temperature.
b. Remove lids and inspect paint for skin-over, gelling,
lumps, etc. Skins, if present, shall be carefully removed
and discarded, retaining liquids which drain from them.
Gelled, lumpy, or otherwise deteriorated paints shall not
be used.
NOTE
Cans of pigmented paint with non-resealable lids
should not be opened and inspected until after the
original mechanical agitation.
c. Thoroughly agitate all pigmented paints, using a me-
chanical agitator prior to thinning and prior to and
during application.
d. Thinning shall be controlled by weight, volume, or
viscosity measurement to obtain and maintain proper
and uniform consistency. Thin according to manufactur-
er’s instructions or the specification for the material.
When the volatile organic compound (VOC) content of
coatings is regulated, thin only with exempt thinner or
solvent, and do not use non-VOC compliant thinners or
solvents such as MIL-T-81772 to reduce high solids
primers and topcoats. Reducing with non-VOC compli-
ant thinners or solvents can cause high solids coatings to
exceed the maximum allowable VOC content in viola-
tion of air pollution regulations.
e. Reduction and/or catalyzation of coatings shall be in
accordance with Paragraph 6.6, Paragraph 6.7, and the
specific coating paragraph as well as the manufacturer’s
instructions. If this does not produce the proper spraying
viscosity, quality control personnel shall be consulted.
f. Strain all material to be used in spray equipment through
fine-mesh strainers or cheesecloth.
6.6 MIXING AND THINNING OF COATING MATERI-
ALS, GENERAL.
Mixing shall be done in controlled areas that are
well ventilated and away from any open flame or
other source of ignition and direct sunlight.
Forced air ventilation, preferable with air flow
from the back of personnel to an exhaust in front
of them. For two component materials, an organic
vapor type respirator shall be worn as a mini-
mum, with the air supplied type being preferable.
Mixing of coating materials may seem too elementary to
require lengthy discussion, but it is a very common source of
trouble either through negligence or lack of knowledge. All
coating materials require preparation prior to application, and
problems with color, gloss, hiding power, film application
characteristics, adhesion, and curing can be expected if
materials are not adequately prepared. For two-component
materials, the components must be thoroughly mixed with
each other and in the exact specified proportions or curing
and adhesion problems will occur. Pigments, which give
color and other desirable characteristics to coatings, are
generally insoluble and heavier than the liquid portion of the
coating material, so they eventually settle out of suspension.
The consistency or viscosity of the liquid portion determines
the rate of settling; for example, pigments mixed with a
thinner alone would settle out in a few minutes; but in a paint
vehicle, it might take months. The practice of thinning too
much material at a time and pouring unused portions of the
material back into the original container with unthinned
material lowers the total consistency and increases the rate of
settling and should not be done. Settled material usually
re-disperses readily unless the material is over-aged or has
become exposed to the atmosphere. In some materials, such
as wash primers and some vinyl based materials, settling may
be accompanied by a change in chemical structure after
storage of only a few months. Such changes are not revers-
ible; therefore, judgment should be employed whenever using
them.
NOTE
After a coating materials shelf life has expired,
thoroughly test material per Appendix A before
using it. If an aged material appears unsuitable
after appropriate attempts at mixing and reduc-
ing, it should be discarded. If the quantity in-
volved is large, laboratory tests by Robins Sci-
ence and Engineering Laboratory to determine its
continued conformance to specification require-
ments will be required before its use or its
disposal.
6.6.1 Method of Mixing. Mixing in containers shall be
done per the following methods:
a. Hand-mixing of single-component materials and the
catalyst component of two-component materials in cans
and drums, per the manufacturer’s instructions using
wooden or plastic paddles.
b. Mixing of one-component materials and the base com-
ponent only of two-component materials in containers
up to five gallons is best accomplished by using me-
chanical shakers that vibrate or shake the unopened
container.
c. Accomplish mixing of one-component materials and the
base and catalyst components of two-component mate-
rials with low speed mechanical paddles.
6.6.2 Mixing Test. A simple test of complete mixing is
to flow samples down an inclined piece of glass. Irregularities
TO 1-1-8
6-2