3-3. CLEANING OF SPECIFIC SURFACES
General. Unless otherwise stated in the end item specification, cleaning shall be accomplished by chemical
methods (such as solvent cleaning, alkaline cleaning, acid cleaning, pickling, descaling with hydride or paint stripping), by
electromechanical cleaning methods (such as electropolishing, electrolyte alkaline, or electrolytic pickling), or by
mechanical means such as blasting, chipping, wire brushing, or grinding. After cleaning, all surfaces shall be kept free
from dirt, dust, finger marks, and other contaminants. Various surfaces, such as ferrous metals, zinc, aluminum and
aluminum alloy, magnesium alloy, wood, and previously painted surfaces, require special handling.
Ferrous Metal Surfaces. Unless otherwise specified, ferrous metal surfaces to be painted shall be blast cleaned in
accordance with Steel Structural Painting Council (SSPC) Specification SSPC-6 to remove milliscale, products of
corrosion, dirt, casting, sand, slag, and other foreign substances. Also, when stated, blast-cleaning shall be in accordance
with specifications SSPC-5 or SSPC-10, as required (see Steel Structures Painting Council Manual, Volume 2, SSPC-
SP6-63 for more information). Blast-cleaned surfaces shall be given a prime coat as soon as possible after cleaning and
in no case more than four hours later. Blast-cleaning shall not be used on surfaces which could be damaged, such as
machine parts and sheet metal thinner than 0.0625 inch (16 gage U.S. Standard).
Blast-cleaning is optional on components painted for protection during limited storage, from which the paint
will be worn off as soon as the equipment is placed in use. Examples are truck assemblies, track roller assemblies
(including mounting frames), interiors of weld-type box sections, bulldozer components (including rippers, scarifiers,
ejectors, push plates, blades, bowls, and buckets), scrapers and crane shovels, interiors of cement mixer drums, and
interiors of aggregate driers. However, these surfaces shall be dry and free from oil, grease, dirt, and rust prior to painting.
Ferrous metal surfaces of vehicles shall be cleaned for painting in accordance with paragraph 3-3b above,
except as specified herein. Surfaces of malleable iron or steel castings shall be cleaned as stated in paragraph 3-3b(1)
above. Other surfaces that cannot be cleaned by blasting may be cleaned to base metal by chipping, powered wire
brushing, or grinding to the required degree specified above for commercial sand blasting. Sheet metal and sheet metal
parts of eight gage and thinner may be cleaned to bare metal by acid pickling in accordance with TT-C-490, with a
maximum of five percent sulfuric acid included. Old paint may be removed from vehicles requiring repainting by the use of
a paint remover.
Zinc Surfaces. Zinc surfaces, including zinc-coated ferrous material, shall be thoroughly cleaned, as specified in
paragraph 3-3a above, to remove all traces of oil, grease, dirt, and other foreign substances.
Aluminum and Aluminum-Alloy Surfaces. These surfaces shall be thoroughly cleaned, as specified in paragraph
3-3a above, to remove all traces of oil, grease, dirt, and other foreign substances. This shall be followed by a three to five
minute immersion or pressure spray in a hot, 10 percent solution of chromic acid, after which the surfaces shall be
thoroughly rinsed with clean, warm water to remove excess chromic acid from cavities, joints, and recesses. The
concentration of chromic acid shall be checked at regular intervals to ensure that the solution is maintained at the specific
strength. Aluminum surfaces that cannot be immersed or sprayed with chromic acid shall be mechanically cleaned,
swabbed with a solution of MIL-C-5541, Type II, Grade B, Class 2.
Magnesium Alloy Surfaces. Magnesium alloy surfaces shall be cleaned in accordance with MIL-M-3171.
Wood Surfaces. Wood surfaces to be painted shall be dry and cleaned of all dirt, oil, grease, and other foreign
substances with a straight, petroleum-aliphatic solvent.
Previously Painted Surfaces. Any coating showing corrosion, cracking, blistering, or flaking must be sanded down
to bare substrate and solvent cleaned. Consider such surfaces bare and treat as required.
For CARC application.