S 366-152
(9)
Mix and apply the Class A sealant as a precoat first. Then mix and apply the Class B sealant. It is not necessary for the Class A precoat to cure before the Class B sealant is applied.
S 366-153
(10)
Always apply sealant within its application time, or "work life". For example, Class A-1/2 sealant has a work life of 1/2 hour or less. Class B-2 sealant has a work life of two hours or less. The work life decreases as tempereature and/or humidity increase.
S 366-154
(11)
Apply a brush coat of Class A sealant.
(a)
Use a small paint brush and work the sealant into all empty spaces (voids).
(b)
Apply the brush coat to an area slightly larger than the area where the Class B sealant will be applied.
(c)
Make sure the brush coat is applied only to cured BMS 10-20, Type II primer or to bare metal. 1) DO NOT apply the brush coat to uncured BMS 10-20 Type II
primer.
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757 MAINTENANCE MANUAL
S 366-156
(12)
Apply the Class B sealant.
(a)
It is helpful to use a pneumatic sealant gun. Certain type of plastic nozzles that are used with pneumatic sealant guns can help you give the fillet seals the correct shape. One type of nozzle has a flat tip that is one inch or less in width. A bench grinder can be used to change such a nozzle to the necessary fillet shape. Fillets applied with a pneumatic sealant gun and a nozzle with a shaped tip are usually better than those shaped by hand. When you apply fillet seals, use the fillet dimensions shown in Fig. 609.
S 366-155
(13)
Repair sealant must look like the shape of the adjacent production sealant.
(a)
Do not apply too much sealant. Too much sealant will make subsequent work in this area more difficult.
S 366-157
(14)
Take a small piece of scrap metal into the tank.
(a)
When the repair is almost complete, apply a small quantity of the Class B sealant onto the scrap metal. Put the scrap metal inside the tank, within arm's reach of the open access door. The sealant on the scrap metal will cure at approximately the same rate as the actual repair sealant.
S 366-158
(15)
Sealant is tack-free when it will not stick to a clean polyethylene film that is pushed lightly against the sealant and withdrawn perpendicular to the surface. When the sealant is tack-free, the tank can be closed.
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