Technical data

Table 4-1. Spray Coating Troubles, Possible Causes, and Remedies - Continued
Trouble Possible Causes Preventive Measures Or Remedies
Crazing, Mud
Cracking,
Checking (Fig-
ure 4-17 and
Figure 4-18).
1. Painting over a hard glossy coat. A base
coat of this condition offers a poor sur-
face adhesion of subsequent coats. In
drying, the topcoat slides over the base
coat, breaking out in cracks.
1. Remove all previous coats of paint using
paint remover or scuff sand, solvent
wipe, and apply a primer tiecoat before
overcoating.
These three defects
are all very
similar in that
they all consist
of surface cracks
in varying de-
grees. Crazing is
a fine surface
crack while
cracking and
checking often
extend to the
metal surface.
2. Excessive amount of catalyst in paint caus-
ing brittleness.
2. Drier should be used only as recom-
mended by manufacturer of material
being used.
3. Excessive heat employed in drying opera-
tion.
3. Exercise caution in placement of heat
lamps to assure uniform heat distribu-
tion over the entire painted area.
4. Insufficient drying times between coats. 4. Allow sufficient drying times.
Slow drying of
Wash Primer
Accidental addition of A-A-857 thinner;
excessive butyl alcohol addition; high
humidity conditions, excessive thickness;
denaturants in the alcohol such as oils,
high boilers, etc., introduced by the acci-
dental use of the wrong alcohol to clean
the surface.
Check mix, using smaller quantities of same
batch, apply to test panel; modify the type
and/or quantity of thinner added and compare
drying times under actual painting conditions;
incorporate use of small test panel adjacent to
all aircraft during complete painting proce-
dure, using such panel for thickness measure-
ments also.
Pinhole Cavities,
Solvent Pop
Improper surface treatment or lack of sur-
face treatment; entrapped oils and/or sol-
vents; insufficient primer drying times;
excessive alcohol additions to wash
primer; use of improper thinner.
Apply manual surface treatment and en-
sure complete coverage with surface
chemical film, before wash primer
and/or primer application; check mixing
instructions to eliminate use of improper
thinners.
Excessive Blush-
ing of Topcoats.
Excessive humidity; insufficient quantity of
Specification blush-retardant thinner
ASTM D330.
Check humidity control equipment where
employed and/or increase quantity thin-
ner ASTM D330.
Peeling Failure to remove moisture, oil or grease
from the surface before the finish is ap-
plied.
Refinish surface.
Blistering (Figure
4-19)
1. Oil or grease on surface. 1. Strip and clean; or sand down and repaint.
2. Moisture in lines. 2. Drain lines periodically.
3. Trapped solvents. 3. Use proper thinner.
TO 1-1-8
4-16