General stripping procedures are described in this section. When you are stripping an aircraft surface, you should consult the applicable MIM for the specific procedures to be used.

Prior to cleaning and stripping, you should ensure the aircraft is properly grounded to dissipate any static electricity produced by the cleaning and stripping operations.

Stripping should be accomplished outside whenever possible. If stripping must be done in a hangar or other enclosure, you must have adequate ventilation. 

Paint remover may contact adhesives at seals, joints, skin laps, and bonded joints. In these areas you should mask with approved tapes and papers. Stripper should be applied liberally with a fiber brush. You should completely cover the surface to a depth of one thirty-second to one-sixteenth of an inch. The stripper should not be spread in a thin coat. A thin coat will not sufficiently loosen the paint. If the coat is too thin, the remover may dry on the surface of the metal.

You should allow the stripper to wrinkle and lift the paint. This may take from 10 minutes to 40 minutes, depending upon the temperature, the humidity, and the condition of the paint. You should remove loosened paint and residual paint remover by washing and scrubbing the surface with fresh water, nonmetallic scrapers, fiber brushes, or abrasive pads. If water spray is available, use a low- to medium-pressure stream of water directly on the surface while it is being scrubbed. After you thoroughly clean the surface, you should remove the masking materials and remove any residual paint.

Rinse the surface with a freshwater and alkaline solution (1 part MIL-C-25769 to 9 parts water) to neutralize the paint remover.

FLAP BRUSH. Paint can be mechanically removed with a flap brush. The brush consists of many nonwoven, nonmetallic nylon flaps bonded to a fiber core. The brush assembly (fig. 14-29) is made up of a flap brush, flanges, and a mandrel. It should be operated by a NO LOAD, 3200 rpm, pneumatic drill motor. The direction of rotation is indicated by an arrow imprinted on the side of the core. When a flap brush has been worn down to within 2 inches from the center of the hub, you should replace it. Continued use beyond this limit may cause gouging due to loss of flexibility of the fiber. When you use a flap brush, apply minimum pressure to remove the maximum amount of paint and the minimum amount of metal. Excessive pressure will cause some paints to melt, gum up, and streak. Eye protection should be worn when you are operating a flap brush. 

SCUFF SANDING. Aged paint surfaces should be scuff sanded to ensure the adhesion of the overcoating paint. Scuff sanding is the roughening of a paint surface as evidenced by a significant reduction of the gloss. To scuff sand, you should use aluminum oxide cloth, abrasive mats, or an oscillating sander with aluminum oxide cloth. Scuff sanding to a depth greater than necessary may result in complete removal of the paint. This situation will expose the underlying metal, and corrosion may develop. Unevenly matched faying surface joints or fasteners and sharply protruding objects or corners should be scuff sanded by hand to avoid sanding through the paint. After sanding, you should remove the residue with a clean, cotton cheese cloth dampened with MIL-T-81772 thinner.

PAINT FEATHERING. You should feather the paint along the edge of an area that has been chemically stripped to ensure a smooth, overlapping transition between the old and new paint surfaces. The smooth overlapping paint film will prevent soil from accumulating in the junction between the old and new paint films. Feathering should be accomplished with 280 or 320 grit aluminum oxide cloth or a flap brush. The major portion of thick paint films may be removed with an oscillating sander with 240 or finer grit aluminum oxide cloth. Do not allow the oscillating sander to touch bare metal. The contact between an operating sander and bare metal will damage the metal, which, in turn, may cause future corrosion. The oscillating sander should not be used after first indications of primer exposure. You should use a flap brush or hand-held 240 grit or finer aluminum oxide cloth for final feathering operations.

TREAT AND SEAL. Chemical conversion treatment is an extremely important part of the corrosion control process. Properly applied chemical treatments impart corrosion resistance to metal. It also improves the adhesion of the paint system. You should use chemical conversion coating materials according to the procedures outlined in the NA 01-1A-509.

Figure 14-29.-Flap brush with mandrel.

First, you should remove all loose seam sealants in the area to be touched up. Replace them as necessary. You should also secure loose rubber seals with the type of adhesive specified in the applicable MIM.

The area to be painted should be outlined with tape and masking paper, as shown in figure 14-30. This protects the adjoining surfaces from overspray and paint buildup.

A standardized paint system for organizational and intermediate level painting and paint touchup has been developed by the Naval Air Systems Command. Standardized exterior paint touchup consists of an epoxy primer (MIL-P-23377, type I or type II) overcoated with aliphatic polyurethane (MIL-C-81773 or MIL-C-83286) or alternate paint system. Paint systems are identified by a decal or stencil located on the right side of the aft fuselage. Standardized interior paint touchup systems consist of TT-P-1757 zinc chromate primer. Paint materials that are within their original shelf life or within an extended shelf life are preferred. However, if materials are beyond shelf life date, you should test them on a small sample of scrap aluminum.