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Why are polyurethane based finishes so unpopular on instruments?
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jsbeddow

Total Topics: 1
Total Posts: 1
I have been reading this forum and others, and am really close to going with one of the WB acrylic lacquer finishes (Target Oxford PSL most likely), but am still intrigued by the lasting popularity of traditional nitro lacquers as well. What am I sacrificing by using one of the WB finishes, and why on earth does no-one even mention the use of any polyurethane finish for guitars? Is it too soft? Not durable? Too plastic looking? Most of the polyurethanes seem to be more UV stable than any other option, so what is it that keeps it from being a popular choice? Are they too difficult to repair--ie. they will not "burn-in" to previous work? Whatever the reason, I have yet to see it mentioned in any guitar finishing forum or website, so if anyone would care to comment, please do so.

Thanks in advance.

Apr 09, 07 | 10:30 pm
Bill Cory

Total Topics: 158
Total Posts: 3584
Hey, JS -- welcome to the forum!

I, for one, have used polyurethane and I have no problem with it. To go even a step further, I've used the easiest, least difficult of all polyurethanes: Minwax WipeOn Poly (gloss and satin), on my ugly duckling Martin Jumbo kit, and I like it. If you go to www.KitGuitarBuilder.com, you will see it mentioned.

I've heard Rick Turner and others recommend it as a fast, easy finish that will last and keep looking good, over on Acoustic Guitar Magazine's Luthier's Corner.

I'm making it a habit to use a new kind of finish on just about every guitar kit I complete. The WipeOn Poly is my fall-back finish, when I want to just move on and not spend a long time finishing.

I think that, simply because it's not a traditional finish used for guitars (except by the Chinese factory beginner models), it doesn't get used much. However, that says nothing about its actual quality as a finish: It goes on thin, is stable, is tough, stays clear, doesn't check, repairs well, needs little or not maintenance ... all good. Basically, those are the reasons the Chinese jobs use it, and it's also very fast to apply and cure.

My nontraditional two cents worth.

Bill Cory
www.kitguitarforum.com
www.kitguitarbuilder.com

Apr 10, 07 | 5:39 am
Ken Cierp

Total Topics: 58
Total Posts: 2262
Nothing wrong with Poly --- water borne or solvent. Keep it thin --- and as matter of fact for those that are compelled to stain. In my opinion there is no better stain system then Minwax oil base with their poly finishes as a top coat --- it is simply hard to beat ---- beautiful. I use that combination for necks, semi or satin, very durable. However, I do not like the Minwax water based stains --- seem to suck the life out of the wood, whereas the oil definitely adds some brilliance and unlocks hidden characteristic in the grain --- silky! I use gallons of Minwax in the furniture end on my business.

Ken

www.kennethmichaelguitars.com

Apr 10, 07 | 3:02 pm
Greenman

Total Topics: 4
Total Posts: 4
Check out Frettech.com he has alot to say about wiping poly. If is works well on electric guitar then why not on acoustics? Most production electric guitars today are Poly if I'm not mistaken it think they stopped using Nitro Laquer in the early sixties. I don't know about what is used on production acoustics? I would rather stay away from spraying Lacquer for my own health and the fire hazardes.

Apr 11, 07 | 4:04 pm
Ken Hundley

Total Topics: 40
Total Posts: 2169
My guess is that you have to be carefull not to spray too many coats, as the Poly may not be as acoustically transparent as laquer, so you are looking at a thinner, and possibly weaker surface than a thicker build of laquer. but again, that is a guess.

Apr 11, 07 | 7:42 pm
Bill Cory

Total Topics: 158
Total Posts: 3584
The Poly I use is not sprayed, but wiped. It is excellent and only requires two thin coats. Minwax WipeOn Poly (Gloss or Satin). I've used it on three guitars and I like it a lot. It is fast, cheap, easy, and goes on in a very hard, very thin coat. To apply it, I put a wad of cotten in a 3x3" piece of soft cotton cloth, make it into a pad and clip it with a tiny clamp. I dip it in the finish and then apply it in straight strips -- one dip=one strip. I overlap by maybe 25%. It goes on without marks or bubbles. I let it dry for one hour, no sanding in between, and put on the second coat. No sanding.

Ends up nice and glossy. You can see it on the Martin Jumbo this page in www.KitGuitarBuilder.com

This was put on over a Target waterbased pore filler (back and sides), and a coat of vinyl sealer. The thickness of that portion of the finish was not detrimental, as the sides in this kit arrived extremely thin (.065 in places). (I didn't know enough at the time I started it to realize the material was so thin.) The two applications of Poly, however, go on thin. I used the satin Poly for the top. The guitar has excellent sound: sustain and resonance are great, and volume is like you'd expect from a jumbo.

Bill

Apr 12, 07 | 5:48 am
Ken Cierp

Total Topics: 58
Total Posts: 2262
Be careful ---- spraying poly will kill you just like lacquer!! Maybe slower -- In my view solvent poly dries too slow to be sprayed. I think the factories that use poly spray the type that is UV cured.

Ken

Apr 12, 07 | 6:02 am
Ken Cierp

Total Topics: 58
Total Posts: 2262
The overseas factories use a lot of Poly therefore it must not be good, right?? Hey! that's just what we thought about Hondas and Toyotas --- Hmmmm

Ken

Apr 12, 07 | 7:02 am
jsbeddow

Total Topics: 1
Total Posts: 1
Thanks to all of you that have replied. I have now picked up my stains (the TransFast powders), and the General Finishes High Performance WB Gloss (acrylic/polyurethane blend), that was highly rated in the Nov/Dec issue of Fine Woodworking. I also picked up the Behlen WB Grain Filler, all from a nearby Woodcraft store. I plan on spraying the gloss finish--any other suggestions from those more experienced than myself? Do I need to consider a sanding sealer after staining? Or, as an alternative, a light coat or two of a fast drying high-solids lacquer to "lock in" the stains before proceeding with my WB finish?

Thanks again, and wish me good luck.

Apr 12, 07 | 9:37 am
Ken Cierp

Total Topics: 58
Total Posts: 2262
The manufacturer of the products you plan to use is the best source of "technical" information --- check with them and tell them what combinations of products you are going to or plan to use. They have all the chemists and the compatibility schedules and charts. Any time I have contacted a supplier they are more than willing to help ---- laying the wrong finishes on top one another can cause a real headache down the road. Your concern that you may be in for a bleed situation is a red light for compatibility. And how would you know if the Poly/actylic is going to stick to the high solids lacquer? Find out the General Finishes recommended process and use it -- you will not be sorry. Two cents

Ken

www.kennethmichaelguitars.com

Apr 12, 07 | 10:26 am
blues creek guitars Authorized Martin Repair Ctr

Total Topics: 52
Total Posts: 1011
There are lots of finishes out there . The reason poly finises most are not accepted by alot of luthiers is that Nitro lacquer and schellac are conidered tradional finishes. I personally prefer lacquer , it is not the fastest finish to completion as the curing time is weeks. The finish is however totally repairable and this is where poly looses some of its shine.
The newer finsishes are getting better but you still can't beat lacquer. Lacquer also has a low acoustic footprint, but the big draw back to lacquer is you do need equipment for spraying buffing and breathing. I don't think any finish is good to be breathing in.Take precautions on all finishing and use the PROPER resperator.
No finish will look good if you don't do the prep right. A poor finish is often the result of a poor prep and fill so do al the steps and learn to do them well for the best result. There is no one perfect finish as we all have our own tastes. Lets face it , finishes are a result of what worked best on production floors.
john hall
blues creek guitars

Jun 04, 07 | 4:30 am
Ken Cierp

Total Topics: 58
Total Posts: 2262
I agree with John regarding the nitro -- if you have the equipment (safety and application) and a good place to spray it is very hard to beat. It is forgiving since each layer actually melts into the previous layer. And as he points out surface prep is the key. Many of the factories have moved to the Polyesters that cure with ultra violet light in seconds --- just like dental fillings! I am not sure if this is practical for the small shop and I understand there are more safety issues. The last time I was to the Martin factory they were still using nitro, their system includes coating pre heaters and driers to reduce production time. At one time I know they used the Sherwin Williams product line. Also keep in mind that a fine guitar can have a finish as simple as a few coats of schellac. We are, after all, building musical instruments choosing to use the basic form as an artist canvas for inlay etc. is an option not a requirement.

Ken

Jun 04, 07 | 5:01 am



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