Polyurethane continued

When you're reading about old fashioned airplanes you will come across references to "spar varnish". I don't know exactly what it was made of, but that's what it was used for.

Well, the Helmsman name is a hint. Spar urethane was developed for flexible parts on boats. Urethanes normally were very brittle before this and would chip under severe flex. As for our planes, I've seen where staining and other things have come through the finish on a friends plane. He thought the reason was he didn't let the Urethane cure long enough before painting over it. I've heard you need to let at least a week go by, longer if it's in a cool climate. The disadvantage of this over the water based is that it is heavier. Since you are going to paint over it anyway, don't worry about the lack of UV protection. If you are planning to use this instead as a clear finish coat, you'd be ok as long as you allow adequate drying. Thin with mineral spirits for spraying, the turpentine will slow the curing even more.

That is not the water based stuff and may even be a little better.

Hello, I've used Helmsman Spar Varnish for years on gun stocks. Nothing is as chemical resistant as this stuff. I don't know for sure about nitro, but oil and gas won't touch it, and neither will the most agressive gun cleaning chemical. Spar Varnish does take a while to cure. Inside at room temp and low humidity (AC on) each coat can take up to a week to FULLY cure. It will get dry to the touch in 24 hours. I always thin it down, and use no ordor mineral spirits. For cleanup, too. Thin about 20% and spray with the lowest pressure you can get (and still flow out the nozzle) to avoid orange peel. Light coats are best, and a plane shouldn't need more than one for sealing. This will also reduce the finished weight some.Lower pressure will also help to keep the air vapors down some, but your wife is going to hate you spraying in the basement. (I spray in a detached building). The vapors are FLAMABLE, so use common sense. Like not near the water heater. With a slow drying time, dust can be a problem. You can't really buff out poly like you can some finishes. Thats why I have a small area walled off with plastic sheeting. Gun stocks have to look good!!! One note; if you paint anything over monocoat (or any other plastic film) you may have a tough time later getting wrinkles out, should they occur. Most paints and poly don't take well to heat.

opinions will vary, jnk

Actually I thought the product name came from a product for ship's spars -- aka boats :-) Aircraft spars are not finished at I as far as I know (perhaps interplane struts, but not spars)..

Bob, Did you use it over another finish? I am looking to use it as a clear coat over a painted finish to provide fuel(gasoline) resistance. Based on the label and other posts it sounds like terrific stuff over bare wood, but I am concerned about applying over a painted surface.

Ed

Bob Bauer wrote:

Nobody has mentioned the caution to test it on a small area first to make sure it is not going to react in a strange way.

Not sure I'd like to try it on any foam construction though.

Beast of luck with your project.

Lee Smith

I might also recommend that you only use the high gloss for any clear coat. The satin has wax in it to dull the finish and it will yellow a lot.(you don't stir the high gloss, but you do the satin, to stir up the yellow wax in the bottom of the can) As a matter of fact, when working on wood, or anything else that needs several coats (like to fill pores in wood), use gloss to build up the coats, and then use satin on the last coat to give the duller finish. Repeated coats of satin will produce a cloudy finish that's somewhat soft as well. Always sand lightly between coats as poly will not bond unless you do, and you will eventually get some delamination.

jnk