MIL-HDBK-1110
6.7.4
Detergent Washing. Detergent washing or scrubbing is
an effective way to remove soil, chalk and mildew. Detergent
cleaning solutions may be applied by brush, rags, or spray. An
effective solution for removal of soil and chalk is 4 ounces of
trisodium phosphate, 1 ounce household detergent, and 4 quarts of
water. For mildew removal, 1 part of 5 percent sodium
hypochlorite solution (household bleach) is added to 3 parts of
the cleaning solution used for chalk and soil removal. Of
course, if there is little or no existing chalk on the surface,
the cleaning solution should not contain the trisodium phosphate.
Note, that sodium hypochlorite solution (household bleach) must
not be added to cleaning solutions containing ammonia or other
similar chemicals. Toxic fumes will be produced. Thorough
rinsing with water is absolutely necessary to remove the soapy
alkaline residues before recoating. To test the effectiveness of
the rinse, place pH paper against the wet substrate and in the
rinse water and compare the pH of the two. (Refer to ASTM D 4262
for complete description of the procedure.) The pH of the
substrate should be no more than one pH unit greater than that of
the rinse water.
6.7.5
Hand Tool Cleaning. Hand cleaning is usually used only
for removing loosely adhering paint or rust. Any grease or oil
must be removed prior to hand cleaning by solvent washing. Hand
cleaning is not considered an appropriate procedure for removing
tight mill scale or all traces of rust and paint. It is slow
and, as such, is primarily recommended for spot cleaning in areas
where deterioration is not a serious factor or in areas
inaccessible to power tools. Hand tools include wire brushes,
scrapers, abrasive pads, chisels, knives, and chipping hammers.
SSPC SP 2 describes standard industrial hand-tool cleaning
practices for steel. Since hand cleaning removes only the
loosest contaminants, primers applied over hand-tool cleaned
surfaces must be chosen that are capable of thoroughly wetting
the surface. Paint performance applied to hand-cleaned steel
surfaces is not as good as that applied over blast cleaned
surfaces.
6.7.6
Heat. Electric heat guns and heat plates are used to
remove heavy deposits of coatings on wood and other substrates.
The gun or plate is positioned so that the coating is softened
and can be removed by scraping. Production rates depend upon the
thickness of the old coating and the smoothness of the substrate.
There is a possibility of creating toxic fumes, or conditions in
which burns are possible. The use of torches is not recommended,
although they have been used to remove greasy contaminates and
paints from surfaces prior to painting. This is an extremely
dangerous procedure. The SSPC no longer has a surface
preparation standard for flame cleaning because of the danger
involved.
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