Instant cure varnish

[Celtic-Grass]

I've seen in some industries (furniture, flooring...)they use varnishes that cure in seconds under ultra violet light. Anyone have any experience with these? are they ever used on instruments either in mass production situations or hand made production?
just wondering. Sounds like a great time saver.

[Big Joe]

UV drying booths have been is use for about fifteen years for curing finishes that I know of (we have used them that long). They will help cure a varnish finish to a certain degree, but it is only certain spectrums of UV light that work. Secondly, you must be very careful about exposure to these UV rays. They can be very harmful...especially to the eyes. Ours was designed to seal and shut off when the door opened. No windows in that booth.

It is not an instant cure for finish though. It will expedite the finishing process, but you are not likely to get an overnight success...especially with oil varnish. For spirit varnish I am not convinced the drying time is that slow to worry about. Just put on thin coats and build them up to the desired thickness.

[sunburst]

Yes, UV cure finishes are in use by instrument manufacturers, notably Taylor guitars. They finish a guitar from start to finish in less than a day. It's a time saver for them, but not those who have to repair the finishes.

[james condino]

Most of the time mandolin finishes fall into the categories of nitrocellulose laquer, catalyzed #polyurethane, french polished or "spirited" varnish that is typically shellac, and traditional violin family oil varnishes. Between my own instruments and working for one of the big production boys, I've built several hundred instruments using all of these methods, except an oil varnish, with very good results.

The ultraviolet cured finished that most of the furniture industry and many of the guitar factories such as Taylor now use is a catalyzed polyurethane that has been specially formulated for this purpose. It requires a special light sealed booth and safety equipment. When set up properly, it will cure that finish in about 20 seconds. The effect is similar to getting one of the new polymer fillings from your dentist- they use a spot uv light probe and cure it in about 20 seconds and you are ready to go chomping on corn nuts again.

Repairs or reamalgamation between new layers of finish are EXTREMELY difficult to hide. Additionally, when we first set up the production booth, several of the fellows in the finish department got second degree burns from the intense UV exposure. I've been to another factory where everyone in the finish department had a great tan all winter long!

Catalyzed polyurethane finishes are thick, and tough enough to bounce a quarter off; great for durability, but not my first choice for tone. I also like to be able to make necessary repairs later.

Typically UV light breaks down lacquer finishes and shellacs with a general decomposition of the material and by darkening the color. That said, my favorite use for the UV light booths is to put a squeeky new nitro or shellac finished instrument in the booth on the "rotisserie" setting with constant turning motion on a low setting #and distressing it. The effect is the same as renting 45 minutes at your local tanning booth and dropping your instrument in it. It sounds a bit extreme, but there are a few customers who won't use an instrument on stage unless it looks like an old bar's wooden dance floor- that vintage bluegrass look.
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j.
www.condino.com

[Big Joe]

Unless you are trying to push a large number of instruments through the finish booth quite quickely a UV booth is not necessary for nitro or spirit varnish. I hate poly finishes for many of the same reasons mentioned above. The cost and work to build a uv booth for casual use is far greater than the few hours it can take the other finishes to dry.

We experimented with a particular spirit varnish and it would dry hard as a rock in a very short time. It was very easy to work with and gave a tone somewhere between lacquer and oil varnish. We never used it in regular production, though there were a few prototypes with this varnish. It was a fantastic product and I wish it would have made it to production. Not to replace the oil varnish or lacquer, but as a different sound.

Nitro dries quite quickly also. We can leave it in the drying booth and respray a few times a day and leave it overnight and it will be ready to sand and buff.

The only thing we used the UV booth for was oil varnish and French polish and experimenting with other finishes or adhesives.

[Celtic-Grass]

Thanks for the info guys! very interesting!

[Mario Proulx]

James, if I may, there's a lot of mis-information in your post.

Taylor's finish is not a polyurethane, but a polyester resin finish. There' a big difference.

Polyester also doesn't have to be thick. The thickness of a finish is the result of what the finisher wishes it to be. If a factory chooses to play it safe, and run a thick finish, it's their fault, and not that of the finish. I use a similar polyester resin finish(but cure it chemically, instead of using UV. Mine cures in hours VS their's in minutes, but otherwise....), and my final thickness has always measured(measured by mic'ing a chip when I remove the finish to glue the bridge or neck) between .002" and .004", never more than that. It often appears thick because of its ability to flow -to- an edge, lending to more rounded-looking edges, and also because of its refractive index(the way it reflects light) and because it doesn't shrink back, thereby remaining smooth. But appearance is often very deceiving. I could rarely get this thin with nitro, back when I could do nitro.... You want thick, look at a Gibson nitro lacquer finish. Yikes! But it's part of their "look"(and I love the way it crazes with age, in large part because of its thickness).

And while polyesters are scratch resistant to a crazy degree, they dent easily when thin, and they are the most flexible finish I've ever seen. Peeling off a few sessions' worth from a soundhole plug measuring over .010'', I can still wrap this around a pencil without breaking, most of the time. At .003", we could probably fold it almost tightly.

So, it's not polyurethane, and it's not thick, unless the user chooses to make it so. And no, you can't bounce a quarter off of it when it's tin. It(the quarter) will surely dent any part of my instruments.

[james condino]

Mario:

Thanks for your perspective. I'll admit that I'm not a chemist, so my nomenclature was off. Whenever I interact with five different luthiers, they all have five completely different ways of accomplishing the same task (and often five different vocabularies). While I have found many of the modern synthetic finishes to have interesting applications, in the production setting that I UV cured them, it was not my first choice. My main concern was the ability to touch up or repair a finish after it had been applied.

I agree with you on the flexibility issue. I have actually been able to pull the finish off an instrument in one hige sheet when removiing it. It was applied approx. .010 -.015" thick- pretty heavy. That's often the case when you work production, following another person's ideas.

I took a look at your website and got a smile from the bio page. Thanks for keeping it lighthearted!
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j.
www.condino.com

[Rick Turner]

I'm with Mario on this. I, too, use catalyzed polyester, and it's thin enough to get that nice grain raising on spruce tops. Mario and I have corresponded extensively on all this.

There is UV polyurethane, but that's not what Taylor, Larrivee, etc. are using.

The ability to touch up nitro lacquer is greatly overstated. I've never seen a touch-up that wasn't glaringly obvious a year after it was done because of continued shrinkage. It may look good the day your client picks the instrument up, but not down the road. I've actually been able to do pretty good spot finish work with polyester. The key is in sanding the surrounding area at 320 or 400 grit, feathering in the finish, and then doing the rubout. You may get a faint witness line, but what you see is what you get and that's what it will be a year from now. With lacquer, you get the burn in, and a year later the whole area looks weird and at least needs a rubout again.

I'm not necessarily advocating polyester for mandolins, but it sure works great for guitars.

[Desert Rose]

Being in the industry and working heavily in instrument finish for thirty years in US factorys and Asian

Id like to second the thanks to Mario for being very accurate

Scott