e . Coating Application . 



(1) Introduction. The goal of coating application is to place a 

 continuous, uniform coating of sufficient thickness that is securely 

 bonded to the substrate. Coating application is initiated after surface 

 preparation has been satisfactorily completed and inspected. The prime 

 coat should be applied promptly after the surface is cleaned, as cleaned 

 steel is easily rusted if it is not protected. Coating application must be 

 made under good dry conditions. If temperature is low enough that drops 

 can occur and cause condensation on the surface, coating application should 

 not be undertaken. 



Coating specifications usually designate that coating work not be 

 undertaken unless the temperature is 3 to 6 Celsius above the dewpoint 

 (the temperature at which condensation will occur at a given pressure and 

 relative humidity). Coating application can be by brush, roller, spray, or 

 dip. 



(2) Brush. Application of coatings by brush is one of the oldest 

 and most widely used procedures for coating application. Maintenance and 

 repair work are frequently done by brush, particularly if the size of the 

 job is small. Most alkyds and a limited number of other products with good 

 wetting properties can be applied by brush. Some manufacturers recommend 

 that the prime coat be brushed on to ensure that it has been worked well 

 into the surface. This is a desirable procedure when the surface is rough 

 or when the surface preparation is poor. 



When brushing is called for, the primer is often thinned to improve 

 flow-out on the substrate. If the surface is rough or pitted, brushing 

 will help work the coating into the roughened surface. The ability of a 

 primer to protect will be directly related to surface wetting. If areas of 

 the surface are not wetted by the primer they will be subject to corrosion. 

 When conditions dictate that a brush be used for touchup work, tacky 

 materials should be applied by liberally filling the brush and quickly 

 applying it to the surface with a minimum amount of brush out. One advantage 

 to application by brush is that there is only 4 to 8 percent loss of 

 material (as opposed to 20 to 40 percent by conventional spray.) 



Brushes must be of best quality and appropriate style. Brushing 

 should be done in such a manner that a smooth coat as nearly uniform as 

 possible be formed. It must be worked well into all crevices and corners 

 and be applied without runs or sags, and with a minimum of brush marks. 



In short, brushing is used by professionals only when it is specified 

 or recommended by the coating manufacturer, where surface preparation is 

 relatively poor, and for touchup work where spraying is unsuitable because 

 of plant or area regulations. 



(3) Roller. This method of application, like brushing, is fine 

 for some materials and poor for others. Roller coating is generally used 

 for applying alkyds and water-based (latex) materials over large areas such 

 as tanks and buildings. These tools are also called into play because of 

 regulations against any spray fog. Fast dry lacquer-type products will dry 

 on the roller and do not dissolve in dipping. Others also show poor flow- 



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