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Polyurethane Finish
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Author:  Pat Hawley [ Sun Dec 02, 2007 6:05 am ]
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Uhmm, is there some problem that I don't know about with polyurethane? And what is the difference between polyurethane and varnish?

I've been doing some testing on scrap with TruOil, French Polished shellac, and MinWax Wipe On Poylurethane and I have to say that, all things considered, at this point I would give the nod to the MinWax Wipe On polyurethane. It goes on easy, looks good (to my eye at least) and is very hard. However, since I never see polyurethane recommended as a finish here, it makes me think there must be something not good about it. Can someone fill me in on this? Thanks.

Pat
Author:  Grant Goltz [ Sun Dec 02, 2007 7:54 am ]
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Don't ever assume that something is "not good" due to lack of mention of it, on this or any other forum

Most likely it has just not been tried much. If it seems to work for you, go for it. There are far too many myths and assumptions in lutherie that get perpetuated mainly because most folks are afraid to try them.

Grant
Author:  grumpy [ Sun Dec 02, 2007 7:55 am ]
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Run your tests on some rosewood scraps.

then come back and ask again <g>
Author:  J.R. Hunter [ Sun Dec 02, 2007 7:57 am ]
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Pat,


Boy, am I glad you asked this question! Been wondering about that myself. I love the stuff. If it works well on furniture etc. why not guitars? There's probably a really good reason, such as: nobody's thought of marketing it to luthiers! ( Oops, I might get in trouble for that one...   )


Looking forward to hearing from the pro's!


J.R.
Author:  grumpy [ Sun Dec 02, 2007 8:13 am ]
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Okay, maybe I was too subtle...

 Polyurethane won't stick to most rosewoods and many other exotic woods without use of a special sealer. So, strike one....

I tested it on a few guitar necks, and while it looked absolutely beautiful on mahogany and buffed easily to a perfect gloss, it wore very quickly(months!). Strike 2.

There are other choices that don't have the other two issues. Strike 3.
Author:  FishtownMike [ Sun Dec 02, 2007 8:33 am ]
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Pat I love the minwax wipe on poly. I use it on a lot of wood working projects. I have used it on guitars though none were rosewood. What Mario says about wear is true if you only wipe on a few thin coats. Remember no one just sprays on two thin coats of lacquer and thats that. You can build up concecutive coats and it will wear very well. The difference between poly varnish and natural varnish is that poly use synthetic resin instead of natural like regular varnish. Natural varnish's use natural resins like pine sap and the likes.
Author:  FishtownMike [ Sun Dec 02, 2007 8:39 am ]
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I forgot to mention that Formbys make a good wiping varnish called Formbys tung oil finish. The name is misleading becaues true tung oils do not harden like a varnish the stay soft in the wood. Formbys tung oil finish dries hard. It contains varnish resins. I would recomend you experiment with this too. Stay away from watcos danish oil and tung oils this stuff never dries and can ooze back out of the poors in warm weather.
Author:  Rick Turner [ Sun Dec 02, 2007 9:01 am ]
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Any formula with a drying oil (and tung oil is one) and resins is by definition an oil varnish. Formby's is one, and the one I like and use is Waterlox. Though it's more or less marketed as an oil finish, the inclusion of both phenolic resin and ester gum qualifies it as a "long oil varnish".   

I use it as as a pre-sealer, aka "tie coat" under McFadden's rosewood sealer, and it not only looks great with it's wetting action, it also greatly enhances adhesion of subsequent coats of just about anything.
Author:  grumpy [ Sun Dec 02, 2007 9:21 am ]
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Mike, the wear issue wouldn't depend on how much you put on. Putting it on thicker would only keep it going longer before it reached wood. At the same thickness as I use with other finishes, it wore through in a few months. Even tripling the thickness would only make it last a couple years, at best.

This surprised me most, since the same stuff on furniture and floors, even is quite tough.

But nobody grabs onto a coffee table with a sweaty hand and holds on tight for 5-6 minutes at a time, repeated for an hour or more at a time. Instruments are quite unique...
Author:  FishtownMike [ Sun Dec 02, 2007 9:57 am ]
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The way the label these wiping finish's can be really misleading. Some use the name tung oil finish when its really a wiping varnish like formbys. Some label them oil finish when they are a varnish finish. And some mislead you to believe it will dry hard like watcos danish oil. This stuff might dry eventually but it can stay wet in the wood for years. The only way to know what you got is to pour some on the lid and wait to see if it hardens or stays oily.
Author:  Rick Turner [ Sun Dec 02, 2007 10:54 am ]
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If they are combinations of oil(s) and resins they are varnishes. The hardness/toughness/flexibility of the varnish is highly manipulable through the exact formula, how it is prepared, etc. Tung oil has an interesting property...it bonds particularly well to cellulose; phenolic resins bond very well to lignin, so an oil varnish made of these components will have excellent adhesion...hence the term "tie coat" when you use such a varnish under other finishes. Oil varnishes tend not to harden like glass, but they do get very tough. I've used practically every formulation on the market, and I find Waterlox to beat them all.   You can use it like an "oil finish"...and yes, it's really a wiping varnish.   I think it would be fantastic under French polish and also under other varnishes like Behlen's Rock Hard.
Author:  FishtownMike [ Sun Dec 02, 2007 12:27 pm ]
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Pat you can make your own wiping poly by buying a can of their poly and cutting it 25% to 50% with paint thinner. I do this because its cheaper to buy a quart can of poly and paint thinner then it is to by a pint can of the wiping poly. This will work with any brand of poly and varnish.
Author:  FishtownMike [ Sun Dec 02, 2007 12:30 pm ]
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Grumpy when you finish rosewood do you wipe it down with any type of solvent like acetone or something else before you finish? I know some people use a solvent on oily woods before finishing and gluing. I have never worked with rosewood.
Author:  grumpy [ Sun Dec 02, 2007 12:45 pm ]
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I tried it straight on, and again under a shellac sealer. Both failed. the polyurethane just wouldn't dry. On the mahogany, it went on fine, and even went on fine over shellac on mahogany. 

It goes back to what Rick said of the oils. Still, it wouldn't have stayed round long with me, as it just wasn't durable. One was "Varathane", and I forget what the other brand was, but another 'name' brand. Both buffed beautifully.

But there are simply way better choices if we have to use an off the shelf canned finish.
Author:  Pat Hawley [ Sun Dec 02, 2007 1:58 pm ]
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I've been testing on mahogany and quilted bubinga. I've also been pore filling with epoxy. For the shellac, I've been using a fresh 2 lb cut I mixed up just recently and also Zinsser's Seal Coat.

I do like the way the TruOil looks on the mahogany and because of the way it feels, I can see why people use it on necks. So I might do that.

One thing I found by accident was that applying shellac prior to pore filling with the epoxy kept the bubinga lighter looking. Without the shellac first, the quilted pattern in the bubinga darkened up quite a bit under both the TruOil and the epoxy. So probably, whatever else I do, I'll start with shellac on the body. At the moment, I'm thinking shellac, then epoxy then the minwax wipe on poly. I'll also see if I can find some Formby's and some Waterlox.

Thanks for your comments.

Pat
Author:  joe white(old) [ Sun Dec 02, 2007 2:01 pm ]
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Pat, you can usually find the Waterlox at Wodcraft if there is one near you.
Author:  Rick Turner [ Sun Dec 02, 2007 2:03 pm ]
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The oils in woods like rosewood and western red cedar act as "anti-catalysts". McFadden's rosewood sealer and other products like "Isolante" are specifically formulated to lock in the oils that prevent polymerization of top coats.

I have to say, I keep seeing these threads where folks want to try something new.   Well, just do it and suck up to the risks of failure if you want to.   However, there are a number of well-proven products that work that have been formulated specifically for the guitar industry, AND THEY WORK! There are those of us who have tried practically everything, have failed to the tune of hundreds or thousands of dollars worth of R & D.   Why the hell reinvent the wheel? What's with this mania of wanting to try Bob Vila's latest wipe-on for pine or whatever they have on sale at Home Depot this week? If you do a modicum of research here and elsewhere on the web, you'll find thousands of words of information and advice on techniques and products THAT WORK FINE!

I for one hereby pledge never again to contribute another word to experimental hardware store finishing threads in my life... Been there, done that, don't give a flying f... if I never see another Ace Hardware finish job again in my life.
Author:  KenH [ Sun Dec 02, 2007 2:14 pm ]
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Has anybody tried Behlen's "Rock Hard" table top varnish on a guitar?


I have used it on tables and other furniture with great success and a beautiful shine, but I havent got brave enough to try it on a guitar yet
Author:  Rick Turner [ Sun Dec 02, 2007 2:18 pm ]
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That's what Bruce Sexauer uses.   He hangs out at the 13th Fret Forum. Lots of info there...
Author:  Hesh [ Sun Dec 02, 2007 2:31 pm ]
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Pat my friend I would caution against using shellac prior to epoxy pore fill/finishing resin.  There has been a lot written here on the OLF prior about how shellac will stick fine to epoxy (french polish) but epoxy does not stick well to shellac. 

Instead just use the epoxy as a seal coat and pore filler all in one.  Also, epoxies like System III and Z-Poxy come in "finishing resins" which are formulated for pore filling.  I hear that West Systems does this very well too but have not used it for pore filling.  Avoid run of the mill hardware store epoxies for pore filling.

System III is extremely sensitive to the mix ratio and you will need a gram scale to use it.  Z-Poxy is more forgiving and now my current favorite for this reason.

If you want to see what an expertly finished guitar with True Oil looks like check out Ron Wisdom's currently running OM thread.  He was able to get a very nice gloss on the body AND that satin feel to the neck with True Oil.  Impressive!!
Author:  Alan Carruth [ Sun Dec 02, 2007 3:20 pm ]
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These days the two finishes I use are French polish (shellac) and Behlen's 'Rockhard' varnish. Generally I agree with Rick on this: stick with something known. I'm a real finish curmudgeon these days.

I see several troubles with polyurethanes, although I have to say there are lots of different ones out there, and they don't all have the same problems. The 'varnish' types I've used tend to share some of the same ones though: I have trouble getting a good shine, and problems with adhesion.

The shine problem has to do with the toughness of the stuff. All of these things have to be leveled and smoothed with abrasives, and at some point as you go finer they just stop cutting. You end up with scratches that can't be rubbed out becuase the finish is just moving aside rather than standing there and taking it like a man, or whatever.

Polyurethanes never seem to stop hardening. If you build up a thick coat the toughness and shrinkage will cause it to let go of the wood. And it's not just rosewoods: I've seen poly finishes on a couple of Santa Cruz guitars that peeled off the mahogany necks like a bad sunburn. The stuff sticks to itself better than it sticks to anything else.

I have also had lots of 'witness line' problems with polyurethanes. That's an issue with many varnishes, but it's worse with the polys, IMO.

The one batch of wiping style poly I got was years ago. Iirc, the lable on the can folded out to about seven pages: the first three were all the risks you were running by having the can in your shop, and then they got into the health and safety problems when you opened it..... Maybe the newer stuff is safer.

For the 'Rockhard' varnish, I thin it out with about 30% of their special reducer (don't use hardware store paint thinner!), 5% acetone, and a few drops per pint of kerosene. The reducer thins it, of course, and makes it prone to run and sag. The acetone allows you to pull it out a thin enough before it flashes off so it won't sag, and the kerosene is a brushing agent that lubricates things and helps it to level. The acetone also helps the new coat to 'bite' into the one under it. The first coat usually takes a day or so to dry, but after that you can put on two in a day, leveling between coats as indicated. When I'm on a roll, I use #1800 Micromesh for that, just to get the dust and 'sand' out, but if I get a run I'll use #360 or #400 sandpaper. Put the last two coats on in as quick succession as you can, and level with Micromesh. If you got the base level enough you won't have any witness lines. Polish out with Novus #3 and #2. Mark Blanchard says that a final rub with Meguire's 'Deluxing' compound really brings up the shine: the last time I saw on of his it looked as slick as a good lacquer job.

Be aware that any oil varnish will have higher damping than shellac or lacquer; the more oil the higher. When I use it on guitars I varnish the B&S, to take advantage of the extra toughness, wear and chemical resistance, and the 'deeper' look that varnish has, owing to the fact that the index of refraction is generally closer to that of the wood. I French polish the tops, as I can get it thinner, and the damping is lower.           
Author:  Rick Turner [ Sun Dec 02, 2007 4:09 pm ]
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Al, SCGC does not use polyurethane, period. All their finishes to date have been some variation on nitro lacquer.   But with nitro lacquer there are huge issues of just how you do pore filling...pre or post first sealer coat, how much time you allow the pore filler to dry...if it's "traditional" oil based filler as I know they use, etc. Also, as Martin has found, the much touted vinyl sealers sometimes just do not provide that tie coat to the wood that something like Waterlox or good old shellac does.

SCGC simply does not allow enough time to do great finishes; and I say this as a friend of Richard and everyone over there. It's simply a matter of fact. They're trying to do nitro finishes in less than ten days, often less than seven, and sorry...you just can't do that.

They are looking into doing UV cured polyester pore filler, and I wish them well. Frankly, they'd do well to ask Addam Stark and me what to do next if that's the way they're moving, 'cause we know how to do four or five day finishes without the expense of UV.

The thing about adhesion is much like doing high quality chrome plating on steel. The good stuff is first plated with copper, then nickel, then chrome.   Each layer bonds well to the substrate and to the next over coat.   So too it is with finishes...tie coat, sealer, build, and last top coat.   Sometimes the materials are the same...as with very traditional French polish, but that tends to take a lot of time. Monica Esparza tells me that Jose Romanillos will take six months to French polish a guitar. That's out of the realm of reality for me and most of us. So my approach has been to figure out different materials for different layers, all of which are extremely compatible with one another.

Monica and I are collaborating on a couple of classicals, and we're going to go with my polyester schedule on back, sides and neck, and then she'll do the egg white ground, French polish top coating she learned from Jose. I may shoot urethane satin on the neck for that nice feel, too.
Author:  Steve Saville [ Sun Dec 02, 2007 4:33 pm ]
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[QUOTE=Hodges_Guitars]

Has anybody tried Behlen's "Rock Hard" table top varnish on a guitar?

.......[/QUOTE]
Yes! It is very good stuff.
Author:  J.L.K. Vesa [ Sun Dec 02, 2007 7:08 pm ]
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Rick,

I am building a shop horse to try out things, and it will get it?s top and back off several times etc.
But, it will go out of my shop to my "test-driver" every now and then so I want it to have some kind of finish that will help it to stay clean and is easy to fix after the alterations. It doesn?t have to be "pretty" but I want it to look desent, still. Another thing is that there will be a finish causing damping in the end product so better to have it in the experimental piece also.

So, I have been thinking using waterlox only for this one. Would you say it offers enough protection and have close enough similar damping properties to say Behlens rock hard?

thanks!

-J.L.K-
Author:  Rick Turner [ Sun Dec 02, 2007 7:13 pm ]
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Just shellac it.
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