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Spraying The Mist Coat by Don Hipskind
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Don Hipskind answers aircraft painting questions in the AXIS HVLP Paint Discussion Board. He operates at AXIS Products - makers of HVLP Paint Sprayer and Fresh Air Breathing Systems.
It's going to be more important on the base coat than the primer
coat because the primer is much more forgiving and will eventually
be hidden but with HVLP we always advise spraying a very light
mist coat or 'tack' coat on the surface. If you don't you will
probably witness runs and sags in the finish which are nasty
things to get rid of. The mist coat, when allowed to dry for
10-15 minutes (until it gets tacky) will act as a magnet and hold
the topcoat to itself. A little practice on a scrap panel will
give you the feel of what I mean.
If you are like most people it will be hard for you to walk away
and leave the mist coat to tack up. If you spray on the overcoat
too soon, the overcoat will tend to sag or run. So go clean the
gun or mix some more paint to use up the time.
When you are ready to spray on the finish primer coat and you are
holding the spraygun in your right hand, begin at the right end of
the panel, wing, fuselage, or whatever and spray a full wet coat
on to the surface working from right to left and don't stop until
you have made a pass from one end to the other. The spray pattern
should be approximately 8" wide and the gun should be held
consistently 90 degrees to the surface 8" away from it. When you
complete the pass release the trigger step back from the work and
see if you are getting full coverage. If you can see through the
coat you just applied increase the fluid flow on the spraygun. If
you are satisfied with the coverage or when the adjustment has
been made begin spraying now from the left to the right end
overlapping the first pass 25% and continue this same routine
until the surface is completely covered.
One thing should be noted here before going on - I will talk about
setting up a paint booth in a future discussion but there are two
things that are an absolute must when spray painting. The first
is to have adequate ventilation so the mists can escape the area
which can be accomplished by using 24" box fan or similar and the
second is to have plenty of light. So many times painters will
feel that they have done a great job only to find light spots and
missed spots when the sprayed piece is brought out into the
light of day. Take a look at a professional spray booth and you
will see what I mean.
When you are satisfied with the job, and well you should be, you
will remember that there is a critical recoat time, usually 24-48
hours. Wait too long and you will have to sand the surface before
you get ready to paint. Recoat before the elapsed time and I
suggest you prepare the primer another way.
Feel free to post comments to the VAF-WWW message board.