ing or when the temperature causes the solution to become too thick to be properly 

 sprayed. Pressure pots should be equipped with an agitator operated by an air 

 motor (fig. 6), which, in addition to performing the work, will accelerate the 

 operation. 



How To Apply Plastic 



In the application of plastic solution the background to be sprayed must be 

 considered. Air pressure tends to blow the plastic through small openings and 

 it is desirable to make the first pass with the spray gun relatively light in order 

 to form a foundation. It has been found that in spraying against webbing, the 

 guns should be held at a sufficient distance (see fig. 17), approximately 12 to 18 

 inches initially, and moved closer on finishing passes, so that the background is 

 not torn or displaced by the pressure. In spraying large solid surfaces the spray 

 gun should be held from 6 to 8 inches from the surface to be sprayed, whereas on 

 cracks or crevices, such as those shown in figure 14, it should be held very close 

 to the surface, diereby eliminating unnecessary coverage. 



The distance at which the gun is held from the object being sprayed affects the 

 wetness or dryness of the application. The greater the distance the drier the 

 resulting coat. A relatively wet application is desirable and should be maintained 

 except where runs are apparent in the application. Wherever these develop 

 either the gun should be held farther away or an adjustment in the spray nozzle 

 should be made. 



In figures 15 through 18, steps in the sealing of an opening are shown. Figure 

 15 shows that the binding agent has been applied directly to the tile wall. The 

 second step shows webbing being applied; the third, the spraying of the finishing 

 coat. In figure 18, the damaged wall is seen to be adequately sealed. 



Backgrounds of Cheesecloth, Paper, and Wire 



In covering large openings, where an excessive amount of webbing solution 

 would be required, cheesecloth or similar material may be used as a background. 

 The basic solution (without webbing) is applied directly on this foundation, and 

 satisfactory results are obtained. In some instances where too much draft or air 

 pressure exists, cheesecloth has a tendency to sag, and this type of application is 

 not satisfactory. 



When many large doors and windows are to be sealed, paper can be applied 

 over the openings and the seams and edges sealed with plastic at a much lower 

 cost than if the solution were applied over large areas. Sisalkraft paper of a heavy 

 grade is desirable. This type of sealing should be used only in protected locations, 

 as the paper seal will not stand exposure to the weather. The use of plastic is 

 recommended when there are relatively few openings of this nature and the 

 material is available, as the cost is not prohibitive, considering the saving in labor. 



Plastic coating should not be sprayed directly against a rigid, porous background, 

 such as wire screen. The air pressure tends to blow the material through the 

 background, leaving minute holes which affect the final result. 



Temporary Sealing of Screened Openings 



In sealing screened doors and screened ventilators it has been found that sisal- 

 kraft paper may be used advantageously. The first step is to apply a margin 

 of binding agent around the frame of the door. Paper adheres to this margin 

 and as a final step the seams and edges are sealed with plastic coating. This 

 sealing gives a gastight result and it is readily removable when fumigation work 

 has been completed. Figure 19 shows an example of this type of application. 



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