This is a continuation of my previously published notes concerning Smooth
Prime and its application. A good subtitle might be " Further Adventures of
a Non-Painter in SprayGun Land".
The initial 2 or 3 coats of Smooth Prime were rolled on for all parts painted
except small metal parts like flap hinges.
As reported previously, I originally tried a Croix CX-9 HVLP system with 40
feet of hose (to cool the air) and a 1.2mm orifice with a 0.7M aircap.
Given the orange peel in the sprayed Smooth Prime using this rig, I borrowed
two other guns and a standard compressor from an understanding friend.
The first gun is a Binks M1-G HVLP with a 1.4mm orifice and a 93PT aircap.
The second gun is a conventional Sharpe Model 90 with a 0.70 orifice and a
#99 aircap; this is a suction feed gun. Both of these orifice/aircap setups
are for spraying automotive urethanes according to the literature. The
Sharpe is 19 years old and has sprayed a lot of paint in its time.
The setup borrowed includes a secondary regulator which was mounted on the
handle of the gun. I removed this and added a 40 inch section of plastic
tube; this allowed the secondary regulator/gauge/filter to be hung from my
belt rather than having to support the weight in hand while painting. This
reduced cleanup since the regulator is not exposed to spray mist. Plus the
hose was out of the way and didn't tend to touch the area just painted.
Using the Croix, I evolved to more than the recommended amount of water to
thin the paint and get less orange peel. With the other guns I thinned as
recommended by Poly Fiber.
The Binks HVLP is rated for operation at 18psi. I found that 45psi was
required to atomize the Smooth Prime. The result was much smoother than the
Croix which has limited pressure available due to its turbine design. The
spray appeared fairly smooth during application but on drying it still showed
orange peel although at a much smaller scale than when applied with the
Croix. The effect is that there are fewer low spots but considerable sanding
is still required to remove them. As with the Croix, there is no appreciable
mist while spraying.
The Sharpe gun is conventional, not HVLP. I found that it worked well at a
bit over 50psi at the gun. Again, the Smooth Prime appeared fairly smooth
when applied. More importantly, it remained fairly smooth when it dried. In
this case, the paint is smooth with raised grains randomly distributed
averaging about 1/2 inch between grains. These are comparatively easy to
remove by sanding, requiring much less effort than sanding orange peel.
There is a small amount of mist in the air while spraying which the exhaust
fan eventually removes.
My paint booth is the garage with plastic sheeting used to wall off an
appropriate area. I clean this area before painting by vacuuming (including
light fixtures, etc) then opening the garage door and blowing the area clear
with high pressure air. The floor is sprinkled heavily with water and I wait
an hour or so with the small exhaust fan in the door running and a furnace
filter in the window before painting. The parts are wiped with Prep Wipe and
then a paper towel before painting. Close examination with a 500w lamp shows
some dust on the parts after all this. Wiping again doesn't seem to reduce
the amount of dust - it acts like static electricity is attracting the dust.
Its hard to say whether this is the source of the grains in the paint since
the dust particles are much smaller than the grains. With the Croix, grains
seemed to form on the nozzle and then get blown onto the surface - this
wasn't obvious with the Sharpe or Binks. Any advice on how to eliminate
these grains would be appreciated.
An opinion from a non-painter on spraying Smooth Prime: The Croix doesn't
appear to be able to atomize this paint. Higher pressure - well beyond
normal- with the Binks HVLP produced inferior results. Despite the
recommendation in Poly Fiber's latest manual, this non-painter would avoid
spraying Smooth Prime with a HVLP rig. An experienced painter could perhaps
get it right, but I certainly couldn't.
Poly Fiber's latest manual suggests a jitterbug type sander for use on Smooth
Prime to speed the sanding process. Apparently, considerable sanding is
normally needed to get a smooth surface with Smooth Prime. Fortunately, it
sands nicely.
Another opinion: the Croix type system with the large low pressure hose is
more difficult to use simply because the hose is much stiffer and heavier
than a high pressure hose. The Binks is the easiest to use of the three guns
I've tried because it's lighter, the trigger feel is smoother, and it's
simpler to change the orientation of the spray fan. Plus, gravity feed means
that no paint is wasted. The Croix is much noisier in use than either of the
other guns - I wore hearing protectors while spraying with the Croix.
I found that Windex, an ammonia based window cleaning product, worked well in
removing paint which had dried on the outside of the gun. Spritz it on, wait
a minute or so, then scrape the softened paint off with a thumbnail or a
toothpick. Clean up immediately since this paint dries very quickly and is
more difficult to remove when thoroughly dry.
For lighting while painting I eventually mounted a 4 foot fluorescent
vertically on a hand truck of the type used to move refrigerators. This
allowed moving the lamp around easily so it could be positioned such that one
could catch the glare in the paint being applied, allowing judgement of when
the paint begins to flow rather than being rough. This technique was tried
with the 500w work light but didn't work nearly as well.
Paint was mixed a cup or two at a time. Since my mixing area doesn't have a
sink, a plastic bucket filled with water was a big help. The stirring paddle,
dip cup, and eventually the mixing container are just submerged until
spraying is done. Then everything is taken outside and hosed off at the same
time.
One thing which didn't work well was thin plastic bags taped in place to
cover the engine and split open to cover the cockpit. The overspray gets
onto the plastic bags and dries. When the next coat is sprayed the air
shakes flakes of paint loose and some land on the newly painted fuselage.
Best to tape some paper or other material to which the paint can stick
permanently next to the margins where the overspray will be thick.
The nib file suggested by Fred Fillinger for removing runs and sags worked
very well. Sags are no longer the major problem for this hacker painter.
Total Smooth Prime used, despite all the trial and error, was 2.5 gallons.
John A044 Newtown, CT
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