MIL-HDBK-1110
f)
Scaffolding for access to work
4.2.3
Safety and Environmental Restrictions.
It will be
necessary to conform to all prevailing safety and
environmental
regulations concerning materials and processes to
be used for
surface preparation and for coating application.
These
regulations are discussed more fully in Section 3
of this
handbook.
4.2.4
Compatibilities. Coating systems must be compatible
with the surfaces to which they are applied. Coating
incompatibility can cause failures at or just after application
or after a much longer time. Failures occurring just after
application are due to solvent incompatibility or wetting
problems. Failures associated with slow chemical reactions, such
as those occurring between alkaline surfaces (e.g., concrete and
galvanized steel) and oil-based paints or mechanical property
mismatches (e.g., a rigid coating applied over a more flexible
one) cause failure in a longer timeframe. The failure more often
is peeling. For existing coatings being repainted, compatibility
generally means that topcoats should be of the same generic type
or curing mechanism as undercoats. One exception to this rule is
inorganic zinc coatings. Since inorganic zinc coatings
frequently do not bond well to themselves, it is safest to repair
them with zinc-rich organic coatings.
A simple test to classify coatings is to determine
solvent sensitivity using an methylethyl ketone (MEK) or acetone
rub test. To do this, soak a cloth in MEK or acetone, rub it
against the existing paint, and visually check for pick up of
paint. The paint is classified as "solvent soluble" if paint is
picked up, and as "solvent insoluble" if not.
Another practical method of ensuring topcoat solvent
compatibility is to coat a small test area of the existing
coating with the paint selected for the work. If situations
permit, this test is preferred over the MEK rub test because it
is specific for the surface to be repainted. The test area
should be visually inspected the following day (or preferably
after 3 or more days) for bleeding of undercoat, wrinkling, loss
of adhesion, or other coating defects. Although most
incompatibility problems are apparent in a couple of days, some
types of incompatibility may not become apparent for several
months or until after a change of seasons. These types are
usually associated with mechanical film properties.
4.2.5
Costs. Life cycle cost has always been one of the most
important considerations in selection of coating systems. Life
cycle costs include original surface preparation, materials, and
application and necessary maintenance throughout the life of the
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