ventilation exists, inside work is generally safe if reasonable precautions are 

 taken (fig. n). 



Effect of Temperature on Application 



An important consideration in this type of work is the atmospheric condition 

 and temperature. Manufacturers of plastics state that the range of temperature 

 for the application of these materials extends from 40 ° to 120 F. Because of 

 the viscous nature of the material and the fact that the major part of the work is 

 performed in the open air, the practical range is probably from 50 to ioo° F. 

 Beyond these extremes, working conditions would be very difficult. 



In addition to the discomfort caused by working under exposed conditions or in 

 unheated buildings, there is the further problem at low temperatures of viscosity 

 of the plastic solution. Greater air pressure is required, and care must be exer- 

 cised in order to avoid excessive application. When temperatures rise above 90 ° 

 F., solvents evaporate rapidly; and in order to obtain a wet application, continuous 

 adjustment of the spray -gun nozzle is necessary. 



As previously stated, it is unlikely that a situation will be found where retarder 

 is required. In isolated cases, however, where the temperatures exceed ioo° F., 

 such as on roofs or on walls exposed to direct sunlight, the addition of methyl iso- 

 butyl ketone, methyl hexyl ketone, toluene, or similar solutions may be necessary. 

 If a retarder is used, care must be exercised in adding it to the solution, as excessive 

 quantities would affect the application and permit the coating to festoon or run 

 before drying. As the solution will be thinner and will dry more slowly with 

 than without retarder, it may be necessary to make an additional pass of the spray 

 gun in order to build up the required thickness. 



Weather — A Problem 



Plastic is difficult to apply in exposed locations during windy weather. Under 

 abnormal conditions, if protection cannot be furnished in the form of a removable 

 screen, it may be necessary to discontinue operations. In view of the fact that 

 webbing consists of spraying fairly light threadlike strands into the air, it is nec- 

 essary to provide protection from the wind. Large plywood sheets, hinged to- 

 gether to form an easily portable screen, have been used effectively as a wind- 

 breaker. Considerable time will be saved if such steps are taken to afford ade- 

 quate protection. If this type of work cannot be protected, it must be delayed 

 until more favorable weather conditions prevail. Plastic coating is easier to apply 

 than webbing and only where extremely high winds occur will any difficulty be 

 found in applying plastic material. 



During rainy periods it is extremely difficult to apply plastic unless the work can 

 be performed under sheds or on the inside of buildings. Plastic will not adhere 

 to wet surfaces; therefore areas to be sealed must be allowed to dry thoroughly 

 before work is continued. 



Oil — Grease — Dirt 



The only other condition under which plastic cannot be applied is on oily sur- 

 faces. If oil or grease has penetrated into building materials, other methods of 

 sealing must be adopted. Where the grease or oil is on the surface and can 

 be removed with kerosene, Stoddard solvent, or other similar materials, satis- 

 factory application is possible. 



It is to be noted at this point that binding agent will adhere readily to all types 

 of dry building materials. In warehouses where deposits of dust and scrap exist, 

 the force of the air pressure from the spray gun tends to clean the surface, and 

 the sealing, in all instances, is effective even under extremely dirty conditions. 



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