Materials required
Table 203
9. MIXING OF SEALANTS
A. Requirements
Sealants shall be mixed in accordance with the manufacturer's recommendations and thoroughly blended before application. All mixed sealant shall be free of entrapped air as possible.
Before either hand or machine mixing, the sealing compound base and its curing agent, both in their respective original unopened containers, shall be brought to a temperature between 21 and 25°C (70 and 77°F) along with all required mixing equipment.
Before mixing, match the sealing compound base batch with the appropriate curing agent batch.
B. Hand mixing
Mix curing agent and compound base intimately.
Weigh the correct quantities of compound base and curing agent in clean jars, as specified.
Mix the two components intimately to obtain a blend with a uniform color and without streaks. Hand mixing requires five to ten minutes to obtain an intimate blend. During mixing, take care to avoid entrapped air due to quick swirls or dashes.
Scrape spatula, vessel jars and bottom regularly.
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Validity : S / N 1 — 9999 20-00-09Page 205
(BA) OCT 97
C. Machine mixing
Mix curing agent and compound base intimately.
Mix the two components with a sealant mixer to obtain a blend with a uniform color and without streaks.
NOTE : Do not exceed eighty revolutions per minute to avoid sealant overheating that would reduce the application time.
D. Extrusion gun packing
Take extreme care when packing the cartridge to avoid entrapped air bubbles. Pack the cartridge fully to expel! all air upwards.
10. APPLICATION (Figures 201 and 202)
A. General
All applications shall be made using the proper type and class of sealant.
Application time of the sealing compound shall be strictly observed. Material which becomes too stiff and difficult to work or which does not wet the surface properly shall be discarded even though the application time has not expired.
B. Fay sealing
Immediately before final closure of the joint, sealant shall be applied to one mating surface of the joint with an extrusion gun or a spatula. Smooth down sealant with a combed spatula to obtain an even film. Apply enough sealant so that the space between the assembled faying surfaces is completely filled with sealant and a small excess is squeezed out in a continuous bead around the periphery of the joint when the joint is secured.
Place parts in assembly position and install fasteners within the application time of the fay sealant. When assembly with permanent type fasteners is not possible, temporary fasteners (sheet holders or bolts) may be used. When temporary fasteners are used, they must be replaced by permanent type fasteners, as called out on the applicable drawing, before the expiration of the work life of the fay sealant. Removal of each individual temporary fastener shall be immediately followed by installation of a permanent fastener. When permanent type fasteners are installed, either after removal of a temporary type fastener or after the expiration of the application time of the sealant used for the fay seal, then sealant shall be applied to the fastener shank or to the hole before installation of the fastener.
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