Please define it.
Spar or otherwise ?
Get a copy of Bob Flexner’s Undertanding Wood Finishing and read chapter 10. He catagorizes varnish into phenolic resins that cure tough and flexible and yellow; alkyd resins that are not as tough but do not yellow as much; and polyurethane combined with alkyd is the toughest, but doesn’t bond well to any other finish including cured polyrethane and degrades in UV light. But he also says "whichever oils and resins are used in making a varnish, the greatest difference is made by the ratio of oil to resin. The more oil, the softer and more flexible the resulting cured varnish film is (spar or marine)to accomodate greater wood movement
Sure, I’ll bite.
It is the dark stains seen on rock formations in the US desert southwest.
Been there, seen that.
The amount of oil (or oil length)
Will have an effect on the final hardness and drying time. The type of oil (Linseed, Soya, Tung, Castor) will also have an effect on the hardness and drying time.
With regard to Polyurethane this is a term abused by the marketing departments as there are many types (2 Pack, Moisture curing & Oxidising) the only common property is that all contain the isocynate molecule.
Did you enjoy the trip ?
It’s the stuff in the carburetors…
…of almost all the small engines that I own that allows my repair guy access to my credit accounts.
I’ve also been told that the truth doesn’t require any.
Something that obscures the truth
simplest def. I’ve heard:
You mean “curing” time, right?
Varnishes don’t dry, they cure as they combine with oxygen. I believe the more technical term is “polymerize”.
depends on the "varnish"
Oil based varnishes are auto oxidative. There are also conversion varnishes as the above poster mentioned, like 2k and acid catalyzed that “cure” if you want to call it that.
Single part spirit varnishes like laquers and shellacs actually do “dry” in the conventional sense.
But really it’s just an exercise in frivolity to stickle on whether your finish is technically “curing” or “drying.” In the end, the product is “dry” to the touch, which probably explains why it is the prevalent and completely acceptable term.
My personal findings
Last year I did a little fact finding at the wooden boat show in Mystic talking to varnish vendors - mostly Epifanes which I posted on the Qajaq site. The main difference between polyurethane (varnish) and Varnish is that polyurethane types are synthetic whereas varnish is made from natural ingredients. Polyurethane was invented for the flooring industry because varnish is not hard enough to take the abrasion. People automatically think that anything that has polyurethane is superior and many manufacturers capitalize on that. Varnish is more flexible as mentioned and better for marine. Spar varnish (named because it was used on sail boat spars) contains mica that reflects back the light and can tolerate the UV. But any varnish or poly that is exterior also has the mica and other reflecting ingredients. They gave me a small sample can of their varnish and It’s the best varnish I ever used as far as gloss retention on my stripper. A bit expensive but really good.
The one interesting fact that came out was that all of the 4 vendors I spoke to said they would use varnish on a SOF and not polyurethane which caused a bit of a outcry on the Qajaq site since everyone assumed Poly was best not realizing that it’s actually less flexible. My feeling is that poly is flexible enough since skin boats don’t really bend that much where the poly would be compromised.
Only thing to add is that there is
a good bit of variation in hardness of both classical and polyurethane varnishes. Some of the latter have really disappointed me by NOT hardening the way I wanted. And, conventional varnishes also can be harder or softer, though (based on a CU review published many years ago), some conventional varnishes can be quite hard.
The technical is polymerise
They still dry however by this mechanism. Other types of coatings dry purely by evaporation of the solvent they are carried in.
what is the purpose of your thread?
It’s starting to remind me of the SNL skits featuring “Nick, Your Company’s Computer Guy”, in which Nick solicits answers from computer users with less knowledge so he can correct & belittle them.
Anybody remember them? I think everyone knows a “Nick.”