Careful planning is necessary to close faying surface seals on large assemblies within the application time limit of the sealant. Once the sealant has been applied, the parts must be joined, the required number of bolts must be torqued, and all the rivets driven within this time limit. When insulating tape has been installed between the faying surfaces to prevent dissimilar metals contacts, pressure sealing should be accomplished by fillet sealing. Fillet sealing is the spreading of sealant along the seam with a sealant injection gun. The sealant should be spread in approximately 3-foot increments. Before you proceed to the next increment, the applied portion of the fillet should be worked with a sealant spatula or tool. See figure 14-45. This working of the sealant fills the voids in the seam and eliminates air bubbles. The leak-free service life of the sealant is determined by the thoroughness and care you use in working out the air bubbles. After the sealant has cured to a tack-free condition, the fillet should be inspected for any remaining air bubbles. Such air bubbles should be opened and filled with sealant. When a heavy fillet is required, it should be applied in layers.   The top layer should fair with the metal. Injection sealing is the pressure filling of openings or voids with a sealant injection gun. Joggles should be tilled by forcing sealant into the opening until it emerges from the opposite side. Voids and cavities are filled by starting with the nozzle of the sealant injection gun at the bottom of the space and filling as the nozzle is withdrawn. Figure 14-45.—Applylng sealant. NOTE: A joggle is a joint between two pieces of material formed by a notch and a fitted projection. Rivets, rivnuts, screws, and small bolts should have a brush coat of sealant over the protruding portion on the pressure side. Washers should have a brush coat of sealant on both sides. Split grommets should have sealant brushed into the split prior to installation. After installation, fillets should be applied to both the base of the grommet and the protruding tube in the pressure side. Sealing Compound MIL-S-8802 This  temperature-resistant,  two-component, synthetic rubber compound is used for sealing and repairing fuel tanks and fuel cell cavities. This compound is designed for an operating environment that may vary between -65°F and +250°F. It is produced in the following classifications: Class A —Sealing material suitable for brush application Class B—Sealing material suitable for application by extrusion gun and spatula Class C — Sealing material suitable for faying surface sealing Dash numbers after the classification code indicate the allowed application time in hours before the curing cycle will have progressed to the point where it is no longer feasible to apply that particular batch of sealant. Class A dash numbers are –1/2 and –2. Class B dash numbers are –1/2, –2, and –4. Class C dash numbers are –20 and –80 (8 hours of application time with the remaining time allowed for working the material). Example: Class A-2 designates a brushable material having an application time of 2 hours. Class B-1/2 designates an extrusion gun material having an application time of 1/2 hour. Class C-20 designates a faying surface sealant with an application time of 8 hours and a working life of 20 hours. Sealing Compound MIL-S-81733 This accelerated, room temperature, curing synthetic rubber compound is used in sealing metal components on weapons and aircraft systems for protection against corrosion. This sealant contains 14-47