catalyzed urethane
 

Hi, it has been brought to my attention that soon there will be no more nitro allowed in the uk, thoughts on an alternative. catalyzed urethane?????

Alister Atkin

taylor uses poly, and so does yamaha. their finishes seem to be long lasting and look good, so i can't see dropping nitro as a huge problem.

I have been using catalyzed urethane for the last 6 years and love the stuff. Unfortunately, it is no longer available from my supplier so I will be switching to catalyzed polyester. Both are great finishes with similar performance qualities. Polyester is marginally harder so you can expect more time behind the buffing wheel.

"Poly" is a term that gets thrown around a lot. There are two very different finishes out there. Polyester resin (poly res) which is often referred to as UV finish. (though it is available in both Catalyzed and UV cured finish) The way it is cured has absolutely nothing to do with the finish. It's just the time it takes for the finish to be ready to ship. Thus someone like Taylor can't afford the time to let a finish gas out so they use UV cured Poly Res. It is a VERY hard finish. (too hard in my opinion) I think the hardness of the finish impedes the movement of the top.
The other "Poly" is polyurethane, which is what you asked about. That's the finish I use. I find it to be a wonderful finish. A little softer than poly res, which as I said before, is a good thing. It is not brittle as Nitro can be. And it's very repairable with CA drop fills. Just make sure you go with a good supplier as urethanes can be very different.

thanks guys
 

Thanks for all your replies. Any idea which makes work well? I used an Italian brand a couple of years ago, used it for a bit and then went back to Nitro. I think now we are going to have to get to grips with Urethane. Im down to my last 16 gallons of Behlens, so a change is on its way. All though from what a lot of the makers iv spoken to say the urethane is easier to use.

I wouldn't say it's easier, or harder.....just different. Most catalyzed finishes shrink less, and cure faster than nitro, so they build faster, requiring less coats than nitro, and less time between the final coat and buffing. My favorite finish is oil varnish. It's not quite as hard as catalyzed urethane or polyester. It needs 40 to 72 hours between coats, with a minimun of 4 to 6 coats. It also takes it several hours to dry dust free so a perfectly clean spraying area is a must. Collings charges an upcharge that's almost the price of the guitar for a varnish finish.

Alister, what catalyzed urethane are you looking at?
The guitar in this thread is finished with ML Campbell catalyzed urethane. It's their "Eurobild" gloss. They have a "wet look" finish but it's not made to be buffed. (the neck is satin).

This guitar is finished with Epifanes Gloss clear varnish.

This guitar is finished with Mcfaddens catalyzed polyester, but Mcfaddens is now out of business.

I believe both ML Campbell, and Epifanes finishes are available in the UK.

Tim, are you going to use reslack? I've got some but haven't tested any yet.

Hi Woody,
No I have some samples of an Italian poly that I will be testing.

There is no one perfect finish and there are a lot of myths out there. I say myths because a lot of generalized garbage is said with authority without any real data to back it up. Stuff like

"Nitro sounds the best"

"I only use shellac because it sounds the best"

"I apply varnish with a brush and my varnish finishes are .0005" thick"

"All guitars with a polyester finish sound like they have a glove on them. (I wonder if this person ever played a Ryan or an Olson.)

"All polyester finishes are thick." (Some are applyed to thick but if done right they can look thick and be just as thin as other finishes. One the guitars that I have used poly on, my tops are about .004" thick. Polyester finish tend to 'build up' on corners (like binding edges) unlike nitro that tends to 'run-away' from corners. This also gives the illusion of a thick finish.)

There are many more myths

My buddy Al told me about a study that was done and published in the Catgut journal by Martin Schleske Without looking it up Al recalled Schleske's main findings:
1) drying oils add damping, and any finish that had oil in it did so,
2) most finishes add at least some stiffness,
3) all finishes add mass,
4) some finishes, such as nitro and shellac, add more stiffness across the grain on spruce than they add mass; the pitches of the (testing) strips rises, and
5) similarly, some finishes, like nitro and shellac, have lower effective damping than spruce across the grain.

Refering to #1 varnish adds some damping (gradually reduces the degree of oscillation, vibration, or signal intensity, or prevents it from increasing) Now some would argue this is a bad thing, but that of course is subjective. I suppose it might be possible to attenuate some 'unwanted' osillations. I think this is done in the violin world.

Refering to #2, this could be a good thing. Most builders talk about finding wood that is stiff, so they remove more material and still end up with the same structural integrety. This is something to take into account when "voicing."

Refering to #3. This one is farily obvious. I often hear builders say "Mass is the enemy." Well I don't completly agree with the statement, but I think maybe we could say "mass in the wrong spot is the enemy," and adding a 'lot' of mass to the top (a very thick finish) is probably not a good thing.

Refering to #4 In this case adding we are actually adding more stiffness than by adding the same amount (mass) of spruce. Still these are small amounts, but it can impact the tone from a voicing standpoint.

#5 is a little surprising to me as I would have thought that any impedance mismatch (the spruce/finish) would cause more damping

This study did not do anything with Polyester and we plan to "play" around with some testing on it. The first test on the poly was inconclusive so some more work needs to be done. I have some samples of Polyester and while the surface is hard is also reasonably flexable so I am not sure how it will fair in the damping and stiffness measurements. Still I would not say that polyester impedes the movememt of the top more than any of the other finishes, but I don't have any data (yet) to back that up.

There is also the more subjective thing and that is about the look. Someone can say with authority, "I like the look of a ntiro finish over the look of a varnish" or vice-verses and not be wrong. Sometimes it about what the customer(s) want and many want that very shinny look that a poly or a (new) nitro can offer.

Anyway, there is more work to be done. There is no perfect finish but there are more and more alternates to nitro. Waterborne (which I didn't mention above) are getting better and better. Good luck in your quest.

Great post John.

Thanks to all the luthiers who posted here -- this discussion was fascinating.

I am chief engineer for a company who makes industrial rotating equipment, and a few years ago we had to change paints to move away from paints with volatile organic compounds (VOCs) for personnel safety reasons. For about 2 years after that we had all kinds of adjustment problems; these days we are using mostly water based epoxy paint. It takes a lot of extra effort to get it right, but when done right, it can be just as good as the old stuff.

I am guessing that if nitro cannot be used in the UK anymore, it most be because of health issues and VOCs.

Regards, Glenn

I have both shellac and nitro finished guitars. The shellac finish ages beautifully but ain't the toughest stuff around.

I know that at one time, companies like Gibson used to spray the nitro in heavy coats because the finish would lose about 1/2 its thickness over the course of the first year. Gibson even used to heat the lacquer to get it on in thick, even coats.

While I don't build 'em, I just play 'em, it is also my understanding that guitar makers have been using plasticizers in nitro since the 1950s. And here in the States, sometime in the 1990s The EPA ordered a reformulation of nitro. I seem to recall Martin having a bit of a slow down or shut down while they reformulated their finish. Point is, the stuff the builders shoot on guitars already contains all kinds of catalysts to make it harder and dry quicker. So maybe it is not as big of a leap going from nitro to a synthetic finish as would be supposed.

I have been using Epiphanes varnish for a couple of years. It works very well for me and doesn't smell as bad as nitro or many other finishes & it cures very quickly. It's made in Holland, so I think you should be able to get it in the UK. I have been buying it from Jamestown Distributors in the US: http://www.jamestowndistributors.com...iphane_varnish
All the octave mandolins on my website are finished with it. It has a very nice glow to it, and can be buffed to a high gloss.
http://jmendelfrets.com/Sub_ForSale.aspx
Good luck finding a new finish that works well for you.
Joe

I never knew someone from Atkin guitars was a member here. Nice too see a UK builder here.

Thanks for all your input chaps.

Do any of you grain fill when using urethane, the only time i used it i followed the tech spec, and it sank really badly after a week. so I think as with all of these finishes, us guitar making people have to play by our own rules. It seems that you almost have to throw and instructions out the window and work it out for our selves. Which i guess we are all used to now any way. I was looking at the bourgeois finish a while back, and i think they told me they use none UV polyester, not played enough bourgeois to get a feel for the sound, Huss and dalton use cat urethane. And Steve McCrarey from Collings told me that Bill said he would go for Urethane in our situation. We are building 80/100 guitars per year. And those of you who supply to shops will understand, most retailer are looking for a flat, strong, shiny finish.

I had an olson in the workshop the other day and thought it looked good, that was the UV polyester i think. And it really does seem to me that like any product it depends who is using it as to the result u get.

I was also noticing the behlens nitro was changing every time we got a new order. 3 years ago it was clear and now its yellow, and getting a little harder to polish.

Anyway, we've got Martha Reeves playing up the road later, so guess i better get a life, get out in the sun and have a few cold ones, and think about this one monday morning.

Over and out for now. :D

You may get more replies over on the OLF http://www.luthiersforum.com/forum/ which is where the builders gather and help each other out a lot.