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Hi, James,
Please take everything I say with a grain of salt since there have
been technical advancements in materials and equipment since I was doing this on
a regular basis. I need to update my knowledge before coating anything on my own
vessel. There are probably some guys on this site that can speak directly to
those points. The polyurethane I was spraying was $250 per gallon 30 years
ago. It was 2-part 1:1 and the preferred solvent was methyl ethyl ketone
(MEK) also called Butanone, however we sometimes used acetone because of
availability. The tip size on our guns was .3 mm to .5 mm. The mix
was thinner than house paints such as acrylic latex. I've also sprayed
acrylic latex with the same equipment, but had to use a larger diameter tip
and thin it (with water) slightly more than the manufacturer's specs.
JOTUN has their own proprietary solvents and I'm not sure what they
contain, however I fully expect that the mix ready-to-spray would be at the
same viscosity I'm accustomed to. I wouldn't even consider using a brush
for a number of reasons; one of those being that it's about impossible to apply
it at a uniform thickness, and that can be critical to solvent release and
curing. I also would not consider using a siphon feed gun or any that use
high air pressures. There are HVLP's that perform somewhat like an
airless. I prefer a remote paint pot with a pressure line feeding paint to
the gun as compared to a gravity feed gun. The reason is that I can
then point the gun straight up, straight down, or at any other angle.
That's handy when you are painting the bottom of something above your gun.
It's also easier to maneuver the gun into tight spaces.
You absolutely must wear proper protective gear including a good-fitting
respirator type mask with fresh charcoal canisters. Also consider
ventilation/filtration, solvent concentration, and all ignition
sources (including vent fan motors). Failure to do so can absolutely
ruin your day.
A common mistake is to locate the inline water trap too close to the
compressor. The air needs some distance after leaving the compressor to
cool enough for the water vapor to condense enough for the trap to catch
it. Otherwise the water vapor passes right through the trap and then
condenses into water droplets that pass through your gun and mess up your
finish.
Learn as much as you can so you can ask well-informed questions, then call
a JUTON tech rep to describe what you plan to do and ask your questions
including "Is Hardtop AS the best one of your company's products to use for
submerged applications?" But also tell him how long at a time you expect
the vessel to be in the water. There are different considerations for
those that sit in the water compared to those that are in for a few hours at a
time and are then hauled out and cleaned. When I finish asking my
questions, I always ask, "What else should I know that I didn't know enough to
ask?" Often that's when I get the most valuable information.
Coating (painting) the interior of the sub for corrosion prevention
deserves as much attention as the exterior. At the end of a day of diving,
you can give the exterior a fresh-water and soap wash down with a pressure
rinse. Can't do that as easily with the interior, and the interior has way
more nooks and crannies.
You can find some info on the net regarding building your own spray
booth. Are you going to have the hull hanging from chains when you spray
it?
That addresses some of the considerations. Hope you
can take the product of my Random Thought Generator and combine it with what the
experts can share with you. Let us know how it works out.
Best wishes,
Jim T.
In a message dated 8/26/2011 9:53:59 A.M. Central Daylight Time,
jamesf@guernseysubmarine.com writes:
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