Technical data

Water to make 1 gal
Chromic Acid Solution (Also known as Dow 19)
Chromium Trioxide (A-A-5587
Type III) (99.5% pure)
11/3oz
Calcium Sulfate 1 oz
(CaSo4
4
•2H
2
O)
Operating Temperature 70° F to 90° F
Container Stainless steel, Alu-
minum, vinyl
Polyurethane or
rubber
Rubber gloves, acid apron, and eye protection
shall be worn by personnel during all mixing
operations.
a. Add chemicals to the water in the order shown, stirring
the solution vigorously, either mechanically or by air
agitation for at least 15 minutes.
b. Apply the solution to a properly prepared surface using
a brush, clean rag, sponge, applicator bottle, or a low
pressure stream (flow-on, do not atomize). Apply the
solution to the surfaces treated with the acid pickle
solution while these surfaces are still wet. Allow the
gross amount of rinse water to run off the aircraft, but do
not wait for complete drying before applying Chromic
Acid Solution, as the oxide film just removed by the acid
pickle solution will reform during this time period and
prevent a proper formation of the conversion coating.
When applying solution to large areas start at the lowest
surface working upward, applying the solution with a
circular motion to disturb the surface film and assure
proper coverage. Agitation shall be accomplished using
a non-metallic acid resistant brush or aluminum oxide
abrasive nylon mat (A-A-58054, Type I, Class 1, Grade
A). Solution works best when applied at 70° F or above.
Leave solution on the surface one to 20 minutes, until a
dark brown coating is produced. Rinse with cold run-
ning water while insuring complete flushing of any
residual materials.
3.1.25 Surface Preparation For Steel. It is essential to
remove rust, scale, oil or other contaminants from steel
surfaces to be painted. The Organic or Inorganic Zinc Rich
primers require good electrical contact with the steel (these
primers provide galvanic protection). To enable this, the steel
surfaces shall be solvent cleaned per Table 3-2, phosphoric
acid treated (Reference TO 1-1-691), or sandblasted. Sand-
blasting to white metal is preferred. Where sandblasting is not
practicable or possible, clean surfaces by means of powered
wire brushes, disc-sanders, grinding wheels or needle scalers.
(Reference TO 1-1-691). Grind sharp edges to a rounded
contour. Remove dust, sand, or grit by vacuuming with a
HEPA filtered vacuum. Follow this with a solvent wipe per
Table 3-2. Clean galvanized surfaces with power tools.
3.1.26 Masking. Masking off areas is almost invariably
required in painting operations on large assemblies or struc-
tures either for protective reasons, as in the precautionary
note below, or for purposes of delineation. In spray applica-
tion of coatings, masking operations may consume more
man-hours than the actual painting.
NOTE
To prevent overspray or paint drift of one color or
material onto another, untreated Kraft paper may
be used to mask or cover areas not specifically
described below where protection of an area
against overspray is the prime consideration.
3.1.26.1 Mask areas such as windows, canopies and large
openings with combinations of tapes and barrier materials:
• Specification MIL-PRF-121, usually a treated paper
which is oil and moisture resistant.
• Specification MIL-PRF-131, usually a laminated foil
and cloth or foil and paper with good water vapor
resistance.
NOTE
Both types above are heat sealable.
3.1.26.2 Pressure-sensitive masking tape conforming to
SAE AMS-T-21595 (formerly MIL-T-21595), Types I
(creped paper backing), II (flat paper backing), and III (plastic
backing).
TO 1-1-8
3-16