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NOTE:  Identify sealant required in the repair area before mixing.
1)  Place amount of base compound to be used on scale and balance with weights.
2)  Add to weights an additional amount of weight to give curing compound-to-base compound ratio called out on manufacturer's sealant container.
NOTE:  The mixing of BMS 5-26, Type II, Class B-2, may be modified by using an accelerator-to-base ratio range of 8.4:100 to 16.8:100 by volume or
10:100 to 20:100 by weight. The 10:100 ratio is standard for B-2 sealant. The 20:100 ratio results in a material with an application time of approximately 1/2 hour and a cure time of approximately 6 hours at 77°F and 50 percent relative humidity.
3) Balance scale by adding curing compound on top of base compound.
NOTE:  Always use curing compound with base compound from same repair kit. Do not mix contents of one repair kit with that of another kit.
4)  Mix curing compound and base compound until homogeneous indicated by sealant of solid uniform color. If mixing machine is not available use clean spatula.
CAUTION:  AVOID INCORPORATING AIR INTO SEALANT DURING MIXING PROCESS.
5)  Place sealant in tube or can which was cleaned with B01013 solvent, series 93 (Ref AMM/SOPM 20-30-93), and sealant is now ready for use.
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(b)  Storing mixed sealant compound
1)  The usability range of mixed sealant may be extended beyond the normal application time by refrigerated storage immediately after mixing. Ensure that sealant to be stored in refrigerator or dry-ice box is placed in sealed container identified as to mix date, sealant designation, class, supplier, and expiration date of usage. Reject sealant stored over 21 days at -41°F (-40°C) and reject sealant stored over 7 days at -20°F (-28.9°C).
CAUTION:  DO NOT REFRIGERATE MIXED SEALANT A SECOND TIME AFTER THAWING.
(4)  
Sealant application time

(a)  The application time of mixed sealant compounds is the usability range of the sealant and is usually designated by a dash number after class, i.e., BMS 5-26, Class B-2 designates sealant with an application time of 2 hours at 77°F and 50 percent relative humidity.

(5)  
Sealant squeeze-out life

(a)  Squeeze out life is the length of time sealant remains suitable for structure assembly in faying surface seal applications. Time, shown in Fig. 804, is the maximum time interval allowed between initial thaw-out of frozen material or mixing of non-frozen material and the final fastening of mating surfaces.

(6) 
 Sealant curing

(a)  Sealant must be allowed a minimum cure time, per Fig. 804, before resuming maintenance operations in tank or filling tank with fuel.
502 
Aug 01/94  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  28-11-0 Page 811 

 

E41493
Sealant Usable Time  502 
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(b)  Ideal conditions for curing are provided by a well ventilated area with ambient temperature of 77°F (25°C). Humidity is a very important factor in cure times and the relative humidity in the area should be known at all times sealant operations are in progress. Desired relative humidity is 50 +5%. Humidity below 40 percent retards curing so that it may be necessary to circulate moistened warm air 120°F (49°C) maximum temperature over the sealed area, or prewarm structure to be sealed, or both. Water added to the air to increase humidity must contain less than 100 parts per million total solids and less than 10 parts per million of chlorides. Curing time may be reduced by circulating warm air, not exceeding 120°F (48.9°C), over sealant or prewarming applicable structure to not exceed 120°F (48.9°C).
WARNING:  USE OF WARM AIR IS EXTREMELY DANGEROUS UNLESS ALL SAFETY PRECAUTIONS ARE OBSERVED. NEVER START OR STOP AIR BLOWER WITH AIR HOSE INSIDE FUEL TANK.
CAUTION:  SEALANT SHALL NOT BE APPLIED WHEN STRUCTURE TEMPERATURE IS BELOW 50°F (10°C) OR ABOVE 140°F (60°C).
(c)  Using the values in Fig. 804 with relative humidity kept constant, times vary according to temperature in that for every 20°F (11.1°C) rise, the tack-free and cure times are approximately one-half as long and for every 20°F (11.1°C) drop, the tack-free and cure times are approximately doubled.
CAUTION:  IF SEALING IS BEING ACCOMPLISHED WHERE HUMIDITY IS HIGH, TEMPERATURE OF METAL SURFACE BEING SEALED MUST EXCEED AMBIENT TEMPERATURE TO PREVENT CONDENSATION OF WATER ON SURFACE TO BE SEALED. THIS SURFACE MUST BE DRY.
　
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