Spar Urethane for finish

[icuker]

I am in the process of refinishing my Papoose (a Uke like instrument with 6 steel strings). The old finish was lifting off (it was a poly finish) and so I scraped and sanded it down and put on some coats of spray shellac. It seemed a little soft and easy to scratch so I steel wooled it down to a matte but would like to put at least a Satin sheen on it. (it looks a little milky white now).

Anyway, the finish folks at Lowe's recommended Spar Urathene since it would protect against moisture better. Is that a good recommendation or should I do something else?

Thanks
Rus

 

[ksquine]

I usually put a couple coats of wipe on polyurethane over shellac. It comes in gloss or satin. I don't know what spar urethane you're talking about but spar varnishes I've used are usually pretty thick stuff and not very hard when cured. Probably not a good product for instruments.
Shellac will harden more over time. It always seems very soft for a few days but hardens up after a couple weeks. I use the wipe on poly to protect against other solvents that can harm shellac...bug spray, sun block, alcohol, etc.

 

[weerpool]

that stuff is way too thick for ukes.

 

[icuker]

Great, thanks. Maybe I could also try spraying it with Shellac again and then using a wax for protection? Otherwise I'll go with the Poly overcoat. Any recommendations for either the wax or poly, brandwise?

 

[Chris_H]

the only reason why spar varnish, or any other varnish for that matter, would be too thick, would be due to insufficient thinning. Oil finishes should be thinned almost 100% of the time, with very few reasons for using oil paints and varnishes straight from the can. Spar varnish does not dry hard, this is what allows it to last in marine environments and sun. Because it remains soft, it will damp the instrument if it is not over built.

 

[Rick Turner]

Use Behlen's "Rock Hard" varnish. Or Epifanes yacht varnish. Both have been used to good effect by guitar makers. Better yet, use Ubeaut hard shellac and learn how to French polish. You can do that over epoxy, too.

 

[thistle3585]

I'll have to disagree, a bit, with Chris only because I know a lot of builders that use spar varnishes on their instruments. I would not say that all spar varnishes are good choices for instruments, as Chris said, but some are acceptable. It really depends on the type of spar varnish and more specifically the ratio of oil to resin content. Higher resin content equals harder, more brittle finish which isn't desirable to use on your mast but would be on an instrument.. Epifanes is a very popular varnish used by instrument builders. Also, KTM offers a waterborne version. The use of the word spar in the description means that it is made to be used in an outdoor environment and stems from the use of varnish on a ship's spars.

 

[Chris_H]

some varnishes I have worked with polish very well, though I would not have guessed varnish as a preferred finish for instruments.

If I were varnishing an instrument I would thin it probably 100%, *equal parts, but more importantly, to feel) or thin enough to yield the desired dry film thickness in 4 to 6 coats, with a rest after 3 or 4 coats, and light wet sanding between coats. Sanding dead flat somewhere past halfway through the process.

Thin it always, strain it always, use drier most all the time. That's what works for me.

I just learned that too thick a finish will diminish the sound of an instrument. I had a feeling I had enough finish thickness at 1 coat of shellac, then 4 fully wet coats of Cardinal lacquer, to cut flat and polish. This sat for 4 or 5 days, then I sprayed 2 more wet coats. The tap tone of the instrument body 'closed' down by maybe 15%, definitely noticeable. It has been sitting now for almost a month. I will try to carefully cut off a substantial amount without burning through prior to the final polish.

 

[icuker]

Ok, then, just so you all realize that this will be a garage amateur finish job. I don't have spray equipment but would be using an off the shelf can to do the job so I wouldn't be able to thin it down. I have four coats of shellac which has been steel wooled down a bit. So, I am concerned that maybe I am getting too thick already?

A friend recommended french polishing what I have now or using a Mequires product and do a hand rub finish. I'm just not sure that on an amateur level I could do a french polish very well. I suppose I could thin down a wipe on product, though, would that be the way to go? (Edit - Sorry, I just realized that Rick's suggestion was a wipe on product)

Thanks, and sorry for any confusion in my descriptions above.

 

[Rick Turner]

And why can't you thin varnish in a garage? As in, "what does that have to do with it?" Boat builders thin varnish all the time anywhere there are boats. Use mineral spirits or pure gum turpentine, or, in the case of Epiphanes, their own proprietary thinner.

The main thing that distinguishes "spar" varnish is not necessarily how flexible or hard it is, but rather the presence of UV blockers which help slow down the deterioration of the finish in sunlight.

Varnish finishes are another one of those "up-charge" line items with guitar makers. I believe the up-charge for a varnished Collings guitar is about $800.00.

Epifanes has a varnish that does not need between coat sanding to achieve a good bond. You have to look carefully at their product line to find it, but it's good.

Varnish can be sprayed or brushed as it usually is by the boatyard folks. You can then level sand and rub it out as with lacquer. If I were back in a small shop with no spray booth, I'd be very tempted to use Epifanes over two or three coats of Smith CPES epoxy as a finish.

 

[icuker]

My point was that if I use a spray can I didn't think I'd be able to thin. But the use of wipe on would surely make it a reasonable thing to do. Any particular tricks to wiping on, any pit falls to avoid?

this will be on top of the sprayed on shellac that's there now.

Hey, thanks for all the help. I do appreciate it.

 

[Rick Turner]

Ahhh, not thin varnish out of a can...you're talking rattle-can shellac spray? Just get some Guitar ReRanch or Stew Mac rattle-can guitar lacquer. BTW, shellac is a wonderful sealer under lacquer OR varnish, but as a sealer you don't need four coats. Two would do fine.

I don't know, it's just not that big a deal to get supplies on line. You don't have to stick with Ace Hardware items. Get the right stuff, and learn how to use it. Or you could sand the shellac nice and flat and then use TruOil over it.

I see newbies coming in and trying to re-invent the finish process time after time, and sorry, but all this stuff is pretty well worked out. The right materials are just a UPS or FedEx truck away.

 

[olgoat52]

The idea behind real Spar Varnish (spar as in Ships mast) was that the the outer layer skinned over but the finish did not harden all the way through. This prevented cracking through the finish when the spar was in use. Now days it probably means something else but that is what it meant when I sold the stuff in a Marine Chandlery. I would think that might dampen the top vibrations.

 

[Chris_H]

I have never seen a varnish I would use straight out of the can. I have always thinned it. Always. Also, I never, ever brush out of the can, always in a clean container, just a small bit more than I need for what I intend to coat. Be very careful in deciding whether to return the unused varnish into the can, and never if it has a drier added.

Yes, 4 coats of shellac is too much as a sealer. 1 to 2 coats is enough, depending on application. In my experience, shellac is a great sealer for lacquer of varnish, and my preference. Too much shellac in the sealing process can cause problems that can take up to a year, possibly more to become evident, if sufficient curing time is not given. I was speaking of a sealer coat of one coat of shellac, and 4 coats of lacquer. When I am spraying, I watch the surface carefully, and spray enough to fully wet the surface without running or sagging. Wet coats are key in spraying lacquer, the 'bug spray wiggle' is not acceptable in spray technique, only intentful, careful application, to fully wet, or possibly a bit more cautious for the first coat.. The spray pattern should not bounce off the surface, and should 'lay in' well. leaving a wet, glassy surface, hopefully also curing to a glassy surface.

No I was not speaking of rattle can spray. I mix flakes in denatured alcohol. I like your idea of high octane grain alcohol, but that sounds dangerous in my shop..... not because of lack of ventilation

I have never seen a varnish that does not benefit from thinning, though I have not used the brands you mention Rick. My experience, and what I would prefer in a varnish product, I think they might still benefit from thinning. I want to buy it slightly thicker than I need, and thin it to exactly what I want at application time. You don't use that stuff anyway, do you.... sorry for no question mark, I am in Costa Rica at the moment, and the keyboard is wacky. Traveling home soon...

If natural bristle brushes are not among your friendly tools, foam brushes may be worth a try.

Olgoat, that is what I know of spar varnish, also.

 

[Chris_H]

I guess I should mention that I have never used any of the 'violin varnishes' or other instrument specific varnishes, mainly higher quality marine varnishes, and higher quality varnishes intended for interior and furniture finishing.

 

[icuker]

So, I'm guessing I should try and steel wool the Shellac down some more and then spray on Stew Mac Nitro or do the tru oil. There is a little bit of orange peel bumps in what I have anyway, so hopefully I can get it smoother. Thanks for all the help.

 

[olgoat52]

If you have bumps, don't count on steel wool to even it out. You need to use a sanding block with some fine paper. say 400 grit wet or dry or maybe 600.

 

[Rick Turner]

What Olgoat said. But you shouldn't have to wetsand. If this is to remain a sealer, sand with 320 to get it done quickly.

 

[icuker]

Good to know. Thanks again for everyone's patience!

 

[Rick Turner]

Once again I'll say "don't reinvent the wheel". All the information you need is at your fingertips. Look to StewMac, for instance. All the instructions and materials to do decent finish work are right there.