MIL-HDBK-1110
Paint should be removed from wood when failure is by
cross-grain cracking (that is, cracking perpendicular to the wood
grain). This failure occurs when the total paint thickness is
too thick and/or the paint is too inflexible. Painting over this
condition almost always results in early failure of the
maintenance paint layer.
Paint removal from wood is difficult
and may not always be feasible. Chemical strippers can be used,
but the alkaline types may damage (chemically degrade) the
surface of the wood and cause a future peeling-paint failure.
Failure caused by a stripper-degraded wood surface is more likely
for exterior exposures than for interior exposures. This is
because the greater expansion and contraction of wood in exterior
exposures requires that the surface wood have a greater
mechanical strength.
6.3.2
Concrete/Masonry. Bare concrete and masonry surfaces,
as well as painted surfaces, are usually best cleaned with water
and detergent. Use low-pressure washing (less than 2000 psi) or
steam cleaning (ASTM D 4258) to remove loose surface contaminants
from surfaces. Use high-pressure water blasting (greater than
2000 psi and usually about 5000 psi) (ASTM D 4259, Abrading
Concrete) to remove loose old coatings or other more tightly held
contaminates or chalk. If existing paints are leaded, special
worker safety and environmental controls will be needed.
Abrasive blasting (ASTM D 4259 and D 4261, Surface
Cleaning Concrete Unit Masonry for Coating) or acid etching of
bare surfaces (ASTM D 4260, Acid Etching Concrete) may also be
used to obtain a surface profile as well as clean surfaces for
coating. Care must be taken to avoid damaging surfaces with
high-pressure water or abrasives. Grease and oil must be removed
with detergents or steam before abrasive blasting. Any
efflorescence present should first be removed by dry wire
brushing or acid washing. Special worker safety and
environmental controls may be needed.
Concrete surfaces must be completely dry prior to paint
application for all types of paints except waterborne. The
plastic sheet method (ASTM D 4263, Indicating Moisture in
Concrete by the Plastic Sheet Method) can be used to detect the
presence of water (i.e., tape a piece of plastic sheet to the
surface, wait 24 hours and look for condensed moisture under the
sheet - the inside of the sheet should be dry).
6.3.3
Steel. The first step in preparing steel for coating
is solvent cleaning as described in SSPC SP 1. Cleaning methods
described in SSPC SP 1 include organic solvents, vapor
degreasing, immersion in appropriate solvent, use of emulsion or
alkaline cleaners, and steam cleaning with or without detergents.
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