thinner at the end of each day's operation. This operation should be performed 

 in the open air whenever possible, but, in any case, where adequate ventilation 

 exists. Hose should be blown out, as it is extremely difficult to clean after the 

 material has hardened When a sealing program has been completed, all equip- 

 ment, including hose, should be carefully cleaned and blown out with compressed 

 air. This operation is shown in figure 23. 



Maintenance 



Plastic sealing is an innovation. Until it becomes well known, the public will 

 continue to be attracted and fascinated by it. It has been observed that laborers 

 and visitors around warehouses that have been sealed continue for some time after 

 its application to pinch and punch holes in the sealing material. Instances have 

 occurred where samples have been removed with the use of a pocketknife or 



PMA 17501 



Figure 22. — Hollow-tile fire wall sealed with plastic. Note the number of cracks 

 and imperfections which have been sealed. 



other sharp instrument. This human curiosity has a tendency to decrease as 

 familiarity with the material increases, and after a period of several months it is 

 reduced to a minimum. In the meantime, however, a considerable amount of 

 patching and replacement is necessary with plastic sealing in order to maintain 

 an effective seal. 



Actual maintenance requirements, due to aging, checking, and normal injury, 

 are relatively small and the belief is that plastic sealing will probably need less 

 care than paper sealing. In connection with the Department's work at Charles- 

 ton, S. C, it was observed that one solid fire door had been moved approximately 

 3 inches without injury to the seal. This indicated that plastic retains its elas- 



29 



