MIL-HDBK-1110
5.7.2.2
Zinc-Coated Steel Tower Components With Deteriorated
Organic Coatings. Zinc-coated steel (either galvanized or
thermally sprayed) with damaged organic coatings should be
scrubbed with a bristle brush to clean the exposed metal surface
and remove loose coatings. The coatings should also be lightly
sanded, if necessary, to feather edge the damaged areas. If the
old paint is oil, alkyd, latex, vinyl or solvent soluble, apply
one coat each of latex primer and finish to the exposed zinc
coating and overlay it 1 inch onto the surrounding tight coating.
If the repaired area matches the intact paint, it will not be
necessary to topcoat the undamaged areas.
If the existing finish coat is polyurethane, epoxy, or
solvent insoluble, apply one coat of epoxy primer and one coat of
aliphatic urethane finish to damaged areas. Again, if the match
is good, topcoating of undamaged areas will be unnecessary.
If an inorganic zinc-primed steel component has
suffered topcoat damage, it should be repaired with the original
topcoat system. If the inorganic zinc primer itself is damaged,
it should be repaired with a zinc-rich epoxy primer (e.g.,
MIL-P-24441, Formula 159) and then given an epoxy intermediate
coat and an aliphatic polyurethane finish coat. Sometimes,
corrosion of the galvanizing has been so severe that underlying
steel is exposed. Such areas should be treated as described
below for steel tower components.
5.7.2.3
Steel Tower Components (With No Zinc Coating) With
Damaged Organic Coating. Steel components of towers that have
never received a zinc coating and currently have damaged coatings
should be hand (SSPC SP 2) or power tool (SSPC SP 3 or 11)
cleaned to remove rust and loose paint. The preferred method of
surface preparation is SSPC SP 11. This method not only removes
all visible rust but also produces a roughened surface so that it
is considered comparable to SSPC SP 6. Powered needle guns and
grinders with flexible wheels and disks can produce the SSPC
SP 11 surface. The steel should be cleaned and primed the same
day, before flash rusting occurs.
If the old paint is oil, alkyd, latex, vinyl or solvent
soluble, apply two coats of alkyd primer to the exposed steel to
a total of 3 mils dry film thickness and overlay it 1 inch onto
the surrounding tight coating. A primer with raw linseed oil
(e.g., SSPC PAINT 25) will penetrate the surface better but dry
relatively slowly. A totally alkyd primer (e.g., TT-P-645) will
dry faster but may not penetrate the surface as well. After
priming, apply two alkyd or silicone alkyd (e.g., MIL-E-24635,
Enamel, Silicone Alkyd Copolymer (Metric)) finish coats at the
same thickness. Two additional coats of primer followed by one
or more latex finish coats can be used instead of the alkyd
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