YVW Dan - the TinBoat website covers all the concerns of Aluminum Boating.
not just the boat itself, but, woodwork, motors, electrical, trailers, wheels,
fishfinder & GPS electronics and "some" basic seamanship guidance
that help the novice boaters get around safely on our waterways.
I have been in and around boats since early childhood and have
learned many things through trial and error (mostly error).
yes - I wrote the articles on primers and varnish vs poly.
I also hang my hat at Wooden Boat.com and LumberJocks.com
which are heavy into fabrication of wooden projects as well as
finishing and refinishing. with the EPA constantly putting intense
pressure on the paint and coatings industry as a whole, it is hard to keep up
with the ever changing product ingredients as well as their performance.
what may have worked like crazy 5 years ago, will not be available today.
the hard oily woods require a specific regiment of varnishing or it will fail.
there are many articles on the Wooden Boat forum that covers teak finishing.
basically ~ teak is sanded smooth and wiped down deeply with acetone before
the finish coats. Epifanes and Pettit Captain's Spar Varnish have the
highest UV protection available (so most say).
Epifanes is as thick as honey and requires considerable thinning.
Pettit is normal viscosity and is more user friendly.
the standard curriculum for Spar Varnish on a boat is:
1st coat ~ 50/50 dilution with 100% mineral spirits.
2nd coat ~ 25% dilution
3rd coat ~ 15%
4th and successive coats ~ 10%
all coats after the 6th coat full strength or cut 5% for easy brushing.
for the fullest UV protection, 8 to 15 coats are required, 24 hours apart.
Teak Oil is not really specifically for teak at all. it is just plain 100% Tung Oil
diluted accordingly and sold as such. the name is strictly a marketing ploy
for sales. example: Tung Oil with a spritz of citrus can be marketed as
Furniture Tung Oil (or Tung Oil Finish) or Furniture Lemon Oil.
Rosewood, Teak, Oak, Cocobolo oils, yada, yada yada are basically the same mixture.
Tung Oil, Boiled Linseed Oil, Minwax Spar Urethane have zero UV blockers.
thus - the aggravation factor kicks in when the finish starts to fail after a
short time when used outside.
my article on Varnish vs Polyurethane is pretty explanatory.
I have a few books on Marine Finishes, Varnishing and Wood Finishing
that I get some of my information from as well as personal lifetime experiences.
I have owned several boats over the years. wood, fiberglass and aluminum.
all have their own unique painting requirements. and all are FUN !!!
sorry for the lengthy response - hope this helps with your project.
(oh, don't just finish the tops of the seats, but the bottoms also).
and as all of us painters know: temperature and humidity have a LOT
to do with how a finish turns out in the end.
but - for natural oils, one must research deeply as to how it will behave
after the project is finished. example: Boiled Linseed Oil is a great preservative
but will actually promote fungus and mildew when exposed to long term moisture
such as up in the PNW or the swamps of Louisiana. Pure Gum Turpentine
is a natural antibiotic so it will resist mildew and fungus in a finish
and should be used as the thinner vs mineral spirits in wet or damp environments.