MIL-HDBK-1110
6.7.2.1
Concrete. Heavy efflorescence and laitance should be
removed from concrete surfaces by dry brushing or cleaning prior
to acid cleaning. This is to prevent dissolution of the
efflorescence and subsequent movement of the salts into the
concrete. Prior to application of an acid solution, heavy oil,
grease, and soil deposits must also be removed. Oily dirty
deposits can be removed by solvent or detergent washing. The
commonly used procedure to acid clean these surfaces is to
thoroughly wet the surface with clean water; uniformly apply acid
solution (often a 5 to 10 percent solution of hydrochloric
(muriatic) acid solution or a solution of phosphoric acid); scrub
the surface with a stiff bristle brush; and immediately rinse the
surface thoroughly with clean water. Measure the pH of the
surface and rinse water using pH paper (ASTM D 4262, pH of
Chemically Cleaned or Etched Concrete Surfaces). In general, the
pH should be within one pH unit of fresh rinse water. It is
essential for good paint performance that the acid be neutralized
before painting. Work should be done on small areas, not greater
than 4 square feet in size. This procedure or light abrasive
blasting can also be used to etch the surface of very smooth
concrete prior to coating. Coating adhesion on slightly rough
concrete surfaces is usually much better than on smooth and
(e.g., troweled) surfaces. An acid etched surface is usually
roughened to a degree similar in appearance to a medium grade
sandpaper. This cleaning method is described in detail in ASTM
D 4260.
6.7.3
Chemical Removal of Paint. Paint strippers can be used
when complete paint removal is necessary and other methods, such
as abrasive blasting, cannot be used due to environmental
restraints or potential damage to the substrate. Removers are
selected according to the type and condition of the old coating
as well as the nature of the substrate. They are available as
flammable or nonflammable types and in liquid or semi-paste
types. While most paint removers require scraping or other
mechanical means to physically remove the softened paint, types
are available that allow the loosened coating to be flushed away
with steam or hot water. If paint being removed contains lead,
additional environmental and worker safety precautions will be
needed. Many removers contain paraffin wax to retard evaporation
and this residue must be removed prior to recoating. Always
follow manufacturer's recommendations. In addition, surrounding
areas (including shrubs, grass, etc.) should be protected from
exposure to the remover, collection of the residue will probably
be required by environmental regulations. Removers are usually
toxic and may cause fire hazards. Management of the waste
associated with the procedure will also be necessary. Consult
the local environmental and safety offices for further
information.
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