Technical data

4.4.1.1 Distance. Distance depends on the desired
width of the paint fan and the type of gun used (Figure 4-7,
Detail A). When all adjustments to the spray gun are correct
and the spray gun is held at too great a distance from the
surface, it will result in a dry spray (dusting) and excessive
overspray. Conversely, if the spray gun is too close to the
surface, it will result in too heavy a coating with a tendency
for sags or runs to develop.
4.4.1.2 Stroking. The essence of proper stroking is to
maintain as near as possible the same distance to the work,
the same speed, and the same perpendicularity of the gun to
the surface throughout the pass. The natural tendency for
spray painters, particularly when fatigued or in an uncom-
fortable position is to arc or wave the gun (Figure 4-7, Detail
B). This practice must be avoided at all costs. In general,
wrist movement must be eliminated in stroking as almost
inevitably, it causes the gun to describe a curve instead of
remaining perpendicular to the surface. This results in a
thicker coating in the middle of the stroke than at the end. An
exception to the rule is spotting in for touch-up. In this case
it is permissible to fan the gun to produce an area which is
thinner at the edges in order to blend into the surrounding
painted area. When applying coating materials with poor flow
characteristics (such as vinyl paints), special efforts must be
taken to hold the gun perpendicular to all surfaces (flat or
contoured). If this is not done, the irregular spray pattern
formed will produce an uneven thickness and cause uneven
drying. Protrusions such as screw heads, etc., present surfaces
that will require facing the gun in several directions to
completely coat them. It may be advisable to spot paint these
in advance. The rate of the stroke should be uniform to
produce a full wet coat of material. Stroking should be in
parallel passes with each stroke aimed for a 50 percent
overlap, or so that the middle of the spray pattern strikes the
wet bottom edge of the previous stroke (Figure 4-8). In order
to ensure good coating integrity and coverage, the technique
of cross coating is best (Figure 4-9). Cross coating should
always be used when applying multiple coats of a coating
system. This is done by applying each layer using the 50
percent overlap and cross coating with each alternate layer of
the coating system, usually after a drying or curing period
between coats. The cross-coating technique is also the stan-
dard for applying a single-coat finish system by applying a
thin, wet-coat followed immediately with another thin cross-
coat to obtain one full wet coat. When applying high solids
primers and topcoats, with HVLP, airless, or air assisted
airless equipment, a single coat using 50 percent overlap
Figure 4-5. Sectional View of Spray Gun
TO 1-1-8
4-7