4. Prepare Adhesive
A. Mix adhesive only as needed and use as soon after mixing as possible.
NOTE: Adhesives are usually supplied in preweighed portions for shop use.
(1)
Type I:
(a)
Thoroughly mix 100 parts, by weight of A-4000 resin with 4.5 parts, by weight catalyst. Use adhesive as soon as possible after mixing. Pot life of A-4000 is 2 to 4 hours at 700F.
(b)
Thoroughly mix 100 parts by weight of PSA-529 adhesive base with 4.5 parts by weight SRC-18 catalyst. Use adhesive as soon as possible after mixing. Pot life of the adhesive is 8 hours at 700F.
(2)
Type II:
NOTE: Type II adhesives, Dow Corning Silastic 731 RTV and Silastic 140 and General Electric RTV 174 are one part adhesives. Each has an indefinite pot life until exposed to air.
(3)
Type III:
(a) Thoroughly mix 100 parts by weight of Dow Corning 93-076-1/2 or 93-076-2 adhesive base with 10 parts by weight of catalyst. Use adhesive as soon as possible after mixing. Pot life of the adhesive is a maximum of 2 hours.
5. Prepare Surfaces
A. Clean both surfaces to be joined, including approximately 2 inches of surrounding area, with clean cheesecloth or gauze pads wet with solvent, Series 88 (ref AMM/SOPM 20-30-88).
WARNING: DO NOT GET SOLVENTS IN YOUR MOUTH, OR YOUR EYES, OR ON YOUR SKIN. DO NOT BREATHE THE FUMES FROM SOLVENTS. SOLVENTS ARE HAZARDOUS MATERIALS. REFER TO PRODUCT MATERIAL SAFETY DATA SHEETS (MSDS) AND LOCAL REQUIREMENTS FOR PROPER HANDLING PROCEDURES.
B. Wipe dry with clean dry gauze before solvent evaporates.
C. Repeat steps A and B as necessary to completely remove dirt, oil, paint and other soils.
NOTE: Clean surfaces are essential for good adhesion.
D. Lightly abrade the area to be repaired with 100 grit, or finer, abrasive to roughen the surface. Remove the particles with a dry cheesecloth.
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E. Apply primer to all surfaces which adhesives are to be applied as follows:
(1)
Spray or brush light coat of Dow Corning 1200 RTV or S-2260 primer on all materials except silicone rubber and air dry for 30 minutes before applying Dow Corning A-4000, Silastic 140 RTV, Silastic 731 RTV or General Electric PSA-529 adhesives.
NOTE: Primer is not required on silicone rubber.
(2)
Spray or brush light coat of Dow Corning 1204 primer on all materials except silicone rubber and dry for 1-24 hours before applying Dow Corning 93-076-1/2 or -2 adhesive.
(3)
Spray or brush light coat of Dow Corning 92-035 primer on silicone rubber and dry for 10 minutes to 24 hours before applying Dow Corning 93-076-1/2 or -2 adhesive.
(4)
Primer is not required before applying General Electric RTV 174 adhesive.
6. Repair Delamination at Joints
A. General
(1) Delamination in a small area (up to 0.50 square inch) may be localized or cover most of that area (extensive). If delamination is localized and the adjoining bond is tight, it may be possible to cut off the delaminated area; if extensive, repair can be effected by use of adhesive. Repairs to delamination in large areas (over 0.50 square inch) may require complete removal and replacement of fabric reinforcement.
B. Repair small delaminated areas (localized in edge of splice and sealing capability is not impaired).
(1)
Cut off loose flap with a sharp knife.
(2)
Feather edge to discourage further peeling.
(3)
Apply a light coat of Type II or Type III adhesive (par. 1.C.(2) or (3)).
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C. Repair small delaminated areas (a maximum of 0.50 sq. in.).
(1)
Pull back delaminated flap and prepare faying surfaces per par. 5.
(2)
Repair seal using Method A (par. 1.B.(1)) with a Type I adhesive (par. 1.C.(1)). Allow 5 to 30 minutes drying time before joining surfaces.
NOTE: The longer times are required at high humidity (over 75% relative humidity) or at temperatures below 650F.
(3)
Press surfaces together firmly to ensure complete contact.
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