(a)  A fuel tank exterior coating for vapor and fuel protection on surfaces exposed to pressurized compartments of the airplane.
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SEALS AND SEALING - MAINTENANCE PRACTICES
1.  General

A.  During the course of structural or component inspection seals are to be examined for deterioration of compound and non-adherence. Any air leakage throughout the pressurized fuselage can normally be detected aurally when carrying out a fuselage pressure check. Fluid leakage can be detected by presence of fluid or fluid stains on the dry side of structural members. For detailed information of fuel leak detection and repair procedure, refer to Chapter 28, Fuel.
WARNING:  AVOID PROLONGED OR REPEATED SKIN CONTACT WITH SEALING COMPOUNDS. USE RUBBER GLOVES WHEN WORKING WITH SEALING COMPOUNDS.
2.  Equipment and Materials
A.  General

(1)  All equipment used for application of sealing compound must be kept clean at all times. All equipment must be cleaned thoroughly after completing each job. Two part sealing compounds, which have been mixed with an activator, will harden and make cleaning of equipment difficult if not removed before they cure. Do not mix tools used with silicone with tools used with non-silicone materials.
(a)  
Cotton coveralls (no pockets, no metal buttons, etc.)

(b)  
Thermal socks

(c)  
Pencil brushes No. 3

(d)  
Varnish brushes, 1 inch and 2 inch

(e)  
Neoprene rubber gloves

(f)  
Unsterilized gauze sponges, (all material shall contain less than 0.75 percent oil - by carbon tetrachloride extraction)

(g) 
 Pipe cleaners

(h) 
 Medicine dropper

(i)  
Polyethylene wash bottles

(j)  
Inspection mirrors - large

(k)  
Flashlight - explosion proof

(l)  
Fillet Fairing Tools - ST 982, A, B, and C

(m)  
Sealant removal tools - made from hardwood or plastic 3/16 inch thick and 8 inches long in 1/4 inch, 1/2 inch and 3/4 inch widths

(n)  
Semco sealing gun, (6 inches length cartridge) Semco Research Inc., Inglewood, California

(o)  
Semco polyethylene nozzles - No. 254, 420, 600E, 620, 640, and 643

(p)  
Semco polyethylene cartridges - No. 250C6

(q)  
Semco Polyethylene Plungers - No. 240P

(r)  
Solvent - Final Cleaning Prior to General Sealing (Series 92) (Ref AMM/SOPM 20-30-92).

(s)  
Methyl isobutyl ketone (Ref 20-30-31)

(t)  
Tape - Permacel Tape No. 70 or 85, or American Tuck Tape No. 210 (Ref 20-30-51)

(u)  
Solvent - Final Cleaning Prior to Aerodynamic Smoothing and Fairing (Series 95) (Ref AMM/SOPM 20-30-95)

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3.  Prepare for Sealing

A.  Determine whether any structural repair is necessary and if so, refer to Structural Repair Manual.
CAUTION:  AVOID BLOCKING OF EXTERIOR DRAIN HOLES AND INTERIOR DRAINAGE PATHS WITH SEALANT.
B.  Examine sealing in area of leakage. Determine the seal level and seal plane in adjacent structure.
NOTE:  The seal plane is defined as being the boundary plane through any assembly of structural items which presents a continuous barrier to flow of fluids or gases.
C.  Identify type of sealant used in area of defect.
D.  Determine type of seal; fillet, faying surface, etc.; which will be required to carry out repair.
NOTE:  Do not interchange sealing compounds. The material originally used has been found to be the most efficient for sealing the area.
E. Completely remove or notch sealant in affected area to produce a solid residual material.
CAUTION:  CUTTING TOOLS SHALL BE OF HARDWOOD OR PLASTIC MATERIAL. METAL CUTTING TOOLS ARE NOT ALLOWED.
F.  Examine rework area for clean cuts and adequate notching and for access. Loose chunks or flaps of sealant on cut areas shall be removed.
G.  Remove grease, oil, dirt, and chips, immediately prior to sealant application, from all surfaces to which sealing compound is to be applied.
NOTE:  The importance of proper cleaning before application of a sealing compound cannot be too highly emphasized. Sealing compound will not stick to a dirty greasy surface. The entire purpose of applying the sealing compound is defeated if it falls off after application.
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