TM 55-1500-345-23
b. Specific guidance on ambient temperature and
acid reaction when alkaline cleaners are used.
humidity ranges for painting with various coatings may
Moistened red litmus paper when applied to the surface
be found in other parts of the TM, in the applicable
shall not react by turning blue. If such color changes
specifications,
or
in
the
manufacturer's
occur, apply a 0.20 to 0.25 percent chromic acid -C-303
recommendations. If not specific guidance is given, the
solution until a piece of blue litmus paper applied to the
general guidance is to not paint below 50F or above
treated surface turns red, which indicates an acid
90F, nor below 40% or above 75% humidity.
surface. Permit the acid solution to remain on the
surface from two to five minutes. Follow with a water
c. The temperature of the surface to be painted
rinse and then wipe dry with clean, lint-free cloths.
must also be considered, and work schedules adjusted
to allow or induce surface(s) to come to the proper
c. Determine whether the surface has appropriate
temperature before applying paint.
surface treatment in accordance with TM 1-1500-344-23.
d. When a special solvent cleaning requirement
SURFACE CONDITION.
Prior to painting,
exists in aircraft painting operations, use Military
inspect or test all metal surfaces for cleanliness and
Specification, MIL-D-16791, TYPE 1, general purpose
physical condition suitable for receiving paint material.
detergent, consisting of 1/2 ounce of detergent in a
gallon of water for wipedown. Then wipedown the
a. The water break test is a method of evaluating
aircraft with isopropyl alcohol, TT-I-735. Additionally,
the degree of cleanness of a metal surface. It is based
each time the painting sequence of an aircraft is broken
on the ability of a clean surface to sustain an unbroken
overnight or longer, this same procedure shall be
film of water. Test representative areas of the surface to
performed immediately prior to application of further
be painted by projecting distilled water on it using an
coats to insure cleanness and proper paintability of the
atomizing device such as a nasal atomizer. Do not use a
surface.
paint sprayer for this purpose as the excessive pressure
will defeat this test. If water gathers into separate
e. Examine for presence of corrosion or foreign
droplets within 25 seconds (that is, if the surface shows a
matter retained in seams and crevices, etc, and for oily
water break) the surface has failed the cleanness test.
films or deposits which may have accumulated after
If, on the other hand, the water suddenly flashes out into
cleaning. If any of these are present, remove or treat as
a film over a large area, an impurity such as alkali
directed in TM 1-1500-344-23.
detergent, etc., is on the surface and it has failed the
test. If the water merges into a continuous film without a
f.
Assure that all metal surfaces and all seams and
sudden flashout, the surface has passed the water break
crevices are dry prior to application of paint. Pressurized
test. A solvent wipedown is not required if the surface
filtered air may be used to dry these areas.
has passed a water break test.
g. Non-metallic surfaces should be dry, free of
b. Insufficient rinsing after cleaning may leave an
contamination; all pores sealed and scuff sanded with an
unacceptable surface. For best adhesion of coatings,
abrasive nylon mat in accordance with Military
metallic surfaces should give either a neutral or a slightly
Specification MIL-A-9962.
