Technical data

the spray gun or brush, tendency to sag or run, drying time,
etc. Volatility also largely governs the flash point of materials.
6.7.2 Thinners.
The very properties that make a substance a good
solvent for organic materials tend to make it
harmful to the body. Many are also hazardous due
to flammability. Use caution to avoid unnecessary
and continued exposure to the volatile constitu-
ents of paints either by inhalation or by skin
contact. Precautions must be taken at all times to
prevent accidental ignition.
Thinner is the material added to a coating material by the
painter to adjust its viscosity. The following specification
thinners are among those used in Air Force painting:
6.7.2.1 A-A-3007, is thinner for enamels such as TT-E-
489, for spray applications.
6.7.2.2 MIL-T-81772 Aircraft Coating Thinner covers
three types of thinners for reducing the standard aircraft
coatings. They are suited for, but are not necessarily limited
to, the following applications:
6.7.2.2.1 Type I is for thinning, MIL-PRF-85285 and
MIL-C-83231/SAE AMS-C-83231 polyurethane coatings, or
other coatings as authorized.
6.7.2.2.2 Type II is for thinning, MIL-PRF-23377 epoxy
primer, MIL-PRF-22750 epoxy coating, or other coatings as
authorized.
6.7.2.2.3 Type III is for thinning, TT-P-1757 primer, or
other coatings as authorized.
6.7.2.3 Special purpose “thinners” are often added to
coating materials to provide good drying characteristics under
abnormal environmental conditions. High boiling point sol-
vents such as diacetone alcohol (ASTM D2627) and butyl
alcohol (ASTM D304) are often added to prevent blushing.
6.7.3 Viscosity. Viscosity is a measure of a liquid’s
resistance to flow. Very viscous or thick liquids such as
molasses flow very slowly, while low viscosity liquids such
as water flow very quickly. Maintaining the proper viscosity
is very important for proper spray application of primers and
paint coatings. Too high a viscosity produces poor spray
patterns and poor coverage, while too low a viscosity
produces a film that sags and runs easily. Many different
methods can be used to measure viscosity, but the easiest and
most frequently used methods for primers and paint coatings
are flow time measurements from either a No. 2 Zahn Cup or
a No. 4 Ford Cup. Therefore, the acceptable viscosity ranges
for each primer and paint coating discussed in this technical
order are given in flow time in No. 2 Zahn Cup and No. 4
Ford Cup seconds at 75° F. For any of these materials, the
viscosity will be somewhat higher at lower temperatures and
somewhat lower at higher temperatures. Viscosity is mea-
sured as follows:
6.7.3.1 No. 2 Zahn Cup. (See Figure 6-1) After the
primer or paint coating is properly mixed, fully immerse the
cup in the liquid so it is completely filled, and lift the cup out
of the liquid. Using a stop watch, measure the time in seconds
it takes the material to flow out of the hole in the bottom of
Figure 6-1. Zahn Cup
TO 1-1-8
6-4