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 for sealants.
 a)  You must know the relative humidity at all times during the sealant operations.
 b)  If the relative humidity is less than 40 percent it slows the cure of the sealant.
 c)  To increase the relative humidity, let moist, warm air, at a temperature of less than 120°F (49°C), flow above the repair area.
 NOTE: In hot, dry climates if you put a pan of
____ water in the fuel tank near the repair area it could add the necessary humidity.
 d)  Make sure the water added to the air contains less than 100 parts per million of total solids and less than 10 parts per million of chlorides.
 2)  If warm, moist air, at a temperature of less than 120°F (48.9°C), flows over the sealant, it decreases the curing time.
 3)  If you increase the temperature of the tank structure, but not more than 120°F (48.9°C), it decreases the curing time.
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747-400
MAINTENANCE MANUAL

 CAUTION: MAKE SURE THE TEMPERATURE OF THE TANK SURFACE THAT
_______ YOU APPLY THE SEALANT TO IS AT A TEMPERATURE EQUAL TO OR MORE THAN THE AMBIENT TEMPERATURE. IF THE RELATIVE HUMIDITY IS LARGE, CONDENSATION FORMS IF THE TEMPERATURE OF THE METAL SURFACE IS LESS THAN THE AMBIENT TEMPERATURE. THE TANK SURFACE MUST BE DRY TO APPLY THE SEALANT.
 4)  For BMS 5-26 Type II or BMS 5-45 sealant, if you keep the humidity constant, the times, shown in (Fig. 804), change as follows for each 20°F (11°C) change in temperature: a) Tack-free times are approximately one-half as long for
 each 20°F (11.1°C) increase in temperature. b) Tack-free times are approximately double for each 20°F (11.1°C) decrease in temperature.
 H.  Apply the Sealant
 S 368-247
 (1)  To apply the precoat do these steps:
 NOTE: A precoat of BMS 5-26 Type II Class A-2 sealant is brushed
____ into the repair area, prior to the fillet seal application.
 NOTE: Precoat is optional when you use Pro-Seal 860,
____ B 1/6 sealant. A special primer is used with PR-1826 sealant. Obey the manufacturers instructions.
 (a)  
Examine the seal area to make sure you have the correct selection of tools for the job.

 (b)  
Apply a precoat of correctly mixed BMS 5-26 Type II Class A-2 sealant to the surface with a stiff bristled brush (Fig. 805). 1) Make sure you apply precoat into all crevices and the full

 length of the area that you will apply sealant to. 2) Apply the precoat at a width of 1/2 inch (12.7 mm) on each side of seams. 3) Make sure the precoat is applied smoothly.

 (c)  
If you let the precoat become hard, clean with Series 93 solvent (AMM 20-30-93/201), before you apply the fillet seal.

 NOTE:____It is not necessary to let the precoat cure. A minimum tack-free time of 15 to 20 minutes is recommended.
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747-400 MAINTENANCE MANUAL
 S 368-249
 (2)  To apply the first fillet seal, do these steps:
 NOTE: You must apply the fillet seal in two applications, a small
____ first fillet seal, and a final fully body, second fillet seal. If you do not use a first fillet seal, fuel leaks can occur in service.
 (a)  Make sure the precoat is applied correctly.
 NOTE: Precoat is optional when you use Pro-Seal 860, B 1/6
____ sealant. A special primer is used with PR-1826 sealant. Obey the manufacturers instructions.
 CAUTION: MAKE SURE YOU APPLY THE FILLET SEAL CAREFULLY TO PREVENT
_______ AIR BUBBLES IN THE SEALANT. THE FILLET SEAL WILL NOT BOND CORRECTLY IF THERE ARE AIR BUBBLES IN THE SEALANT.
 (b)  
Apply a small fillet seal of BMS 5-26 Type II, Class B or BMS 5-45 Class B sealant (or equivalent) with the sealant gun (Fig. 806). 1) When you use a nozzle tip, point the nozzle tip into the

 seam, almost perpendicular to the direction of travel. Keep a bead of solvent in front of the nozzle tip.
　
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