MIL-DTL-53072E
3.3.6 Blasted steel armor. On blasted ferrous armor substrates that have Rockwell C hardness
(HRC) greater than 39, wash primer containing phosphoric acid shall not be used. This is due to
the risk of hydrogen embrittlement from the phosphoric acid in the component B of the wash
primer. In lieu of wash primer, TT-C-490, type I, qualified pretreatments to TT-C-490 types III
and IV not containing phosphoric acid or zinc-rich primer conforming to A-A-59745 shall be
used as the pretreatment. Refer to 3.2.1, abrasive blasting of ferrous metal surfaces, for
alternatives to hexavalent chromium containing pretreatments. For blasted ferrous substrates
greater than HRC 42, prior approval from the contracting officer shall be received before zinc-
rich primers are used as an alternative. Refer to TT-C-490 for embrittlement testing and stress
relief for steel alloys at Rockwell C hardness (HRC) 39 or greater. Applying Zinc-rich primer to
ferrous substrates with a hardness rating greater than HRC 42, is prohibited unless the contractor
submits a request for deviation and receives approval.
3.4 Priming. The primer shall be applied to a clean, dry surface within 24 hours of cleaning and
pretreating. The preferred temperature range for the application of these primers shall be 60 to 90
ºF (16 to 32 ºC). If priming is done outside of this range, then all quality control checks shall be
done (see 4.2.3) to verify film integrity. The paint and surface shall be approximately the same
temperature and not less than 50°F (10°C). When surface temperature or air temperature is < 5 ºF
above dew point, the coating is adversely affected. At relative humidity in excess of 50%, a dew
point calculation may be necessary to avoid the formation of moisture on the substrate to be
coated. Application shall be by brush or spray, depositing a continuous, adherent film which is
smooth, uniform, and free from runs, sags, or other defects that might interfere with the
application and adhesion of subsequent coatings (see 4.2.3.8). The film thickness requirement of
each primer is specified in table V. If paint heaters are used to assist in application, the substrate
to be coated shall be at least an ambient temperature of 60 oF (16 ºC). Dipcoating is not a
recommended application method for CARC primers. The anticorrosive primers are primarily
epoxies and two component products. The powder coating primers are epoxies, but are one
component materials. The zinc- rich primers are either two component epoxies or one component
moisture cured urethanes. They are applied to metal substrates to provide corrosion resistance and
a surface to which the CARC coating system firmly adheres. The two component products dry by
a two stage process of solvent evaporation and chemical crosslinking, and they have a finite
potlife, typically 6-8 hours. Environmental conditions, particularly temperature and relative
humidity, can affect potlife, curing, and adhesion. In areas where air quality regulations restrict
volatile emissions, do not add thinner to the coating material if that addition exceeds the
regulatory limit. If thinner needs to be added, consult with the manufacturer of the primer for the
appropriate thinner to stay within the regulatory limits. The specific information below for the
seven primers is summarized in table II. If a contract requires the use of zinc-rich primer, then
MIL-DTL-53022 or MIL-DTL-53030 shall be applied over the zinc-rich primer as a barrier coat
between the zinc-rich primer and the topcoat. In addition to the liquid primers, there is also an
epoxy anticorrosive powder coating primer (MIL-PRF-32348) that can be used in the CARC paint
system. When a contract specifies the use of either MIL-DTL-53022 or MIL-DTL-53030,
alternative primers MIL-DTL-53084 or MIL-PRF-32348 are authorized for use only with the
approval of the contracting officer.
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