High viscosity paint produces paint sag and orange peel, while low viscosity paint produces improper flow out and waste of thinner. To avoid these problems, take care to measure the proportions of thinner and paint accurately in a graduated measuring cup.
The temperature at which the spraying is done is also an important factor in turning out a good job. This applies not only to the temperature of the shop but also to the temperature of the vehicle. Shop temperatures should be maintained at approximately 70F. Whenever possible, bring the vehicle into the shop well in advance of painting so that it becomes the same temperature as the shop. Spraying paint on a surface that is too cold or too hot from being in the sun will upset the flowing time of the material and will cause orange peel and poor adherence to the surface.
Another important factor in doing a good job is the thickness of the paint film on the surface. Obviously, a thick film takes longer to dry than a thin one. As a result, the paint will sag, ripple, or orange peel. Ideally, you should produce a coat that will remain wet long enough for proper flow out. but no longer. The amount of material you spray on a surface with one stroke of a gun will depend on the width of the fan. the distance of the gun from the sprayed surface, the air pressure, and the amount of thinner used.
In addition, the speed of the spray stroke will also affect the thickness of the coat. The best procedure is to adjust the gun to obtain a wet film, which will remain wet only long enough for good flow out. Get the final thickness by spraying an additional coat after the first one has dried.
Nearly all-standard spray guns are designed to provide optima coverage when held at a distance of 8 to 12 inches from the surface to be painted. When the gun is held too close, the air pressure tends to ripple the wet film, especially if the film is too thick. If the distance is too great, a large percentage of the thinner will be evaporated in the spraying operation. Orange peel or a dry film will result. because the spray droplets will not have opportunity to flow together.
It is imperative, then. to hold the spray gun at the specified distance from the work. In addition, do NOT tilt or hold the spray gun at an angle. Also, never swing the spray gun in an arc. but move it parallel to the work. The only time it is permissible to fan the gun is when you want the paint to thin out over the edges of a small spot. Figure 8-68 shows the method for using a spray gun.
Another ingredient that is sometimes added to the paint is "drier." This substance causes the paint to set and dry much more rapidly than normal. Because a small amount of drier is all that is required, the instruction on its use must be followed closely. Mixing paint and adding drier are two critical parts of painting vehicles. Use of the wrong type of thinner, paint, or excessive drier will cause the paint to fade. peel, or blister within a short period of time after completing the job.
Painting instructions for using chemical agent resistant coating (CARC) and the camouflage painting of CESE equipment are found in the NAVFAC P-300.
Epoxy fillers (body fillers) are simple to use in that the body portions do not have to be straightened as closely as when making repairs without it. By using the manufacturer's instructions, you can apply body filler over rough places and form it with a body file or sanding until it conforms to the desired contour.
The advantage of using body filler lies in the fact that a badly damaged vehicle can be returned to a like-new appearance quickly and with a limited amount of metal straightening. Additional, the use of thinner metals in the bodies of modern vehicles makes it difficult to reform panels into their original shape.
Should you have an opportunity to use an epoxy filler. the recommended thickness of the filler should be kept to approximately 1/8 inch. If more is required. it should be applied in coats and allowed to dry before applying the next coat. Do not exceed an overall thickness of 1/4 inch.
Once a vehicle has been repainted, you will be required to replace the vehicle identification markings. The placement of registration numbers and other equipment markings for identification purposes, as required by law, are described in the NAVFAC P-300 and COMSECOND/COMTHIRDNCBINST 11200.1.
Civil Engineer Support Equipment (CESE) is assigned to many locations where atmospheric and environmental conditions can cause severe corrosionContinue Reading