MIL-PRF-24635E
4.5.22 Water resistance. Two panels shall be prepared in accordance with 4.4.1. A film of coating shall be
applied to both test panels by drawing down in accordance with ASTM D823 to the manufacturer's recommended
total system DFT. The coating film shall be allowed to cure to service in accordance with the manufacturer's
ASTM F718 sheet at referee conditions. Exposed uncoated metal surfaces shall be coated with wax or a primer in
accordance with MIL-DTL-24441. One panel shall then be immersed in distilled water at 73±2 °F (23±1 °C) for 18
hours in accordance with ASTM D1308. The exposed panel shall be examined for blistering in accordance with
ASTM D714, and visually compared to the second, unexposed panel.
4.5.23 Accelerated weathering. Two panels shall be prepared in accordance with 4.4.1, with the exception that
the panels shall be 4 by 6 by 0.125 inches of cold rolled steel. The coating being tested shall then be applied to the
panels by drawing down films of coating in accordance with ASTM D823 to the manufacturer's recommended total
system DFT. The panels shall be allowed to cure to service in accordance with the manufacturer's ASTM F718 data
sheet at referee conditions. The initial color of the test panels shall be measured in accordance with ASTM E1347
on any suitable instrument. The initial 60-degree gloss of the test panels shall be measured in accordance with
ASTM D523. The panels shall be exposed for 300 hours to accelerated weathering using a Fluorescent UV-
Condensation type apparatus in accordance with ASTM G154. The cycle shall be 4 hours of UV exposure using a
UVB-313 bulb at 140 °F (60 °C) and 4 hours of condensation exposure at 104 °F (40 °C). After exposure, color and
gloss shall be measured again in accordance with ASTM E1347 and D523. The color difference shall be calculated
in accordance with ASTM D2244, and the gloss change shall also be calculated. Any chalking shall be evaluated in
accordance with ASTM D4214.
4.5.24 Anti-stain. Four steel test panels shall be prepared in accordance with 4.4.1, with the exception that the
panels shall be 4 by 6 by 0.125 inch cold-rolled steel. The coatings to be qualified shall be applied to one side of
three of the four test panels in accordance with the manufacturer's ASTM F718. The fourth panel shall be coated on
one side with one of the Grade C products currently listed on the Qualified Products List for this specification (the
"control"). All four panels shall be coated on the reverse side and around all edges with one coat of
MIL-DTL-24441 Formula 150 green primer to achieve four mils DFT. All panels shall be cured for 7 days at
referee conditions. Three evenly spaced 0.125-inch holes shall be drilled through the coating to the steel substrate,
but not through the steel plate. These holes shall be located 0.75 inches from one of the 4-inch edges ("the top") of
the specimen. One hole shall be centered between the panel edges, and the other two holes located one inch to either
side of the center hole. All four panels shall then be exposed in accordance with GM9540P, Method B for 100 days.
After the 100 day exposure period, the panels shall be removed, and the vertical length of running rust streaks shall
be measured on both the control panel and the three coating system panels.
4.5.25 Long-term exterior exposure. Four test panels shall be prepared in accordance with 4.4.1. The coating
being tested shall be applied to the required total system DFT and allowed to cure to service in accordance with the
manufacturer's ASTM F718 sheet between applications of each coat at referee conditions. The painted panels shall
be cured for at least 7 days prior to mounting on the test rack. After this cure period, the 60-degree gloss for each
panel shall be determined in accordance with 4.5.17 and recorded. Test specimens shall be mounted on a test fence
having a 45-degree south facing rack at a distance of not greater than 100 feet of an ocean high tide line. The
exposure shall be in accordance with ASTM D1014. The fence shall be at a facility approved by the qualifying
authority. Prior to initiating the test, photograph the wall of test panels (include a gray color scale in all photos and
develop photographs to the scale). The test panels shall be exposed for period of 1 year. All panels shall be
evaluated for checking in accordance with ASTM D660, cracking in accordance with ASTM D661, blistering in
accordance with ASTM D714, and chalking in accordance with ASTM D4214. The 60-degree gloss for each panel
shall again be determined in accordance with 4.5.17, and recorded. The gloss measurement for a panel after
exposure shall be divided by the gloss measurement recorded before exposure for that panel, and the result
multiplied by 100 percent to obtain the percent gloss retention for each panel. The percent gloss retention for all
four panels shall be averaged, and the result recorded. Two of the exposed panels shall then be tested for adhesion
in accordance with ASTM D3359, Method A for coatings with a total system DFT of greater than 15 mils, and
Method B for coatings with a total system DFT of 15 mils or less. If the total DFT is between 5 to 10 mils, the
spacing between the lines in the Method B cross-hatch shall be doubled. If the total DFT is between 10 to 15 mils,
the Method B line spacing shall be tripled.
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