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Some people can not wear polyester shirts, because it stinks really bad when they sweat. Do guitars finished in it have the same problem Stuart? I have read that KTM-9 water based polyurethane dissolves a bit and gets sticky because of some peoples sweat too, and over time it becomes a tacky, bubbly, discoloured mess and needs to be removed and refinished with something else. Of course nitrocellulose is famous for similar reactions but normally over a much greater period of time. I have seen some nasty nitro finishes on vintage instruments that were stored with little to no ventilation, and even some pick guards turned into gel for the same reason, because it never really stops out-gassing.

Chemical based polyurethane is plastic when cured, and can last longer than the instruments owner. Water based has not been around long enough to tell for sure what time will do to it. Seeing that the thrift stores still have plenty of ugly 70's polyester shirts in great condition, it to may just last forever !

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If what you see is what you get, then Stevie Wonder ain't got nothin'!

Hehe...

I would think that a polyester finish would be non-reactive...it being a catalyzed, and therefore inert, finish. I haven't had complaints but I only have a few guitars out there with it.

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I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

I thought the shirts to be inert too back in the "Big collar" days, but boy, I got one for Christmas once and ever since then I steer clear of them! Nothing beats good ole' cotton.

Nitrocellulose is made with cotton. Take a cotton cigarette filter, burn one end under a lighter until it shows a small green flame, then squish it in between two hard surfaces with a lot of pressure, and it will turn really hard (like a nitro finish). Someone told me that it used to be a way to make little cutting blades in prisons, and with enough of them you could make a larger blade, and use it to add a murder conviction to your sentence!

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If what you see is what you get, then Stevie Wonder ain't got nothin'!

Stuart,

Could you go over the pore filler you are using?

As for the urethanes, One main reason I'm attached to Enduro-Var is the finish color. But you really need to do it all in a day. The possibility of creating witness lines is just too much of a risk.

When you consider the 1/2 hour dry time between coats, you can get a lot on in a day.

I just read up on Enduro-var, and they do not recommend using it over any other products but stains, or "at your own risk" so I would guess pore filling and sander sealer are out of the question. They say that it is self sealing, but do not mention whether or not it can fill huge pores like paduk has. It does sound worth trying though, when you are going for an amber tone.

I wonder if it can be used as a pore filler too, like the first water based polyurethane LMI used to carry, but discontinued after it did not live up to the hype. It required thinning with water for finishing, but unthinned, it was like yoghurt, and worked great as a pore filler. To bad it had a nasty milky bluish cast, and was not very durable or hard enough for guitars.

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If what you see is what you get, then Stevie Wonder ain't got nothin'!

Mike, how many coats are to doing in a day? What is the process you use in between coats? The reason I ask is I will be doing this tomorrow for the first time with an earlex sprayer. I used zpoxy for the pore fill and have it leveled and cleaned up and ready to go.



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Answer below but I thought you might want to see this before you get too excited. There are potential downsides to using polyesters...and the wrong kinds of urethanes. I do impact tests on every finishing test. It's simple enough....just heavy carbide endmill dropped backwards down a 8' length of pipe at 80%. That leaves a dent about as deep as acrobatic lead singer swinging a mic stand. It's about .08" deep at the real stress point (the edge) and that impact load tapers off to zero over the course of about .75"....so you can see how the impact looks over the range 0-Max.

These would be HARD repairs in polyester vs. a nitro over shellac schedule depending to a large extent on the pore filler you used under the shellac...and how IT handles such an impact.

The photo titled "allpoly" is all Simtec...their filler and topcoat.

The photo titled "partpoly" is 8 coats of lacquer sprayed over fully cured Simtec poly sanding sealer.

Even using nitro....this would STILL be a miserable repair...assuming anyone could make the crescent shaped tear along the impact line disappear. I'd be interested in how to do that...btw.

I use the allpoly schedule so nobody has to wait for nitro to dry.

Point here....you can leave NASTY sanding swirls in the poly sanding sealer on BOTH the lacquer and poly topcoats. NASTY ones....150 grit blossoms....and you can't find a line to save your life on these test panels...or a guitar. This is the best indication I can give you as to whether you'll see witness lines sanding...but it certainly is optimistic for both lacquer and poly topcoats over this sanding sealer.

Schedule:

1. Bare wood - 150 orbital - 240 with grain....the orbital lines here...you want to remove these from the wood. Clean WELL with naptha then never touch it with your bare fingers again. And don't wait for airborne crap to pollute it again either. Seal it as soon as you can after it has been cleaned.

2. Simtech 28x50 Sanding Sealer - catalyzed first - THEN mixed 20% with acetone (bond MIGHT improve slightly with styrene instead of acetone...not likely though). Sprayed thin at 90 degrees across the face...then immediately again at 180. Two quick, thin coats.

(I'm using a cheap HVLP throughout all of this. I'm PRETTY sure it's a 1.1mm orifice but it could possible be a 1.3mm. I can't tell you for sure. The perfect acetone ratio can probably be found with either orifice to get it to lay down thin...and not pool or run.)

3. One hour later do it again.

4. One day later, provided you had 65 degrees in your shop overnight, level with orbital - 150 grit. get every speck of gloss...and your done.

5. Provided you didn't sand through....there IS no step 5. If you DID sand through you'll have to put on another sealer coat and try it again.

6. Clean baby...with acetone or naptha...naptha is cleaner...less residue I'm pretty sure.

7. Spray Simtec 27x6 A-18 Super Clear topcoat using the same crossover technique...no acetone thinner with the topcoat.

8. Wait an hour...do it again.

9. Wait an hour...do it again.

9.5. Don't do it again....it builds up enough in steps 7., 8. and 9.

10. Cure overnight +65 F. More is better though...up to 80 F. You don't need to bake it.

11. Level and polish in the morning. no kidding.

That's the REAL HARD topcoat you are looking at on the allpoly photo.

You can also use Simtec 37x4 Super Clear (not on their web site) as a topcoat. I use 37x4. I couldn't find the test panel I made with that. Doesn't matter. The schedule is exactly the same as the other topcoat except for this:

You can use the very same leveling and polishing schedule with the 37x4 that you use for nitro...so that eliminates a big learning curve and maybe some new equipment.

_________________
I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

See the flat, reflective area...about the same relative size on both photos? See the four main stress cracks below them on each photo?

Those panels were all made out of the same board of Peruvian Walnut...so they have the same density.

Those two impacts and finishing processes happened on WAY different days... and the difference between the two impacts couldn't have varied by 5%...if that.

You know what this tells you?

When you control the production environment of modern catalyzed polymers you can make airplanes out of them.

In the case wood finishes, you get a VERY predicable, VERY beautiful film of really clear plastic over wood. It is what it is....but it's WAY faster and, in my opinion, far more predictable than nitro.

I wish it wouldn't crack like this but note that a LOT of the area DID stick to the wood without topcoat separation either. This was an intentional impact MEANT to wreck the finish. If you don't get impacts hard enough poke holes in your acoustic tops then scratch resistance is your next issue...and this stuff is absolutely great in that regard. Some of the urethanes are even better.

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I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

Thanks, Joe, for weighing in. I have only sprayed catalyzed finishes on metal, and then I didn't do spot touch-ups. It's good to know it can be done. Maybe we make a false distinction between a "molecular" bond, and a "mechanical" bond. I think adhesion is more complicated than that. Certainly, a finish that can "melt in" makes invisible repairs easier. But many adhesives can bond powerfully to slick surfaces (hide glue, for one). Any insights you can share about spot touch-ups on catalyzed finishes would be welcomed.

I'm pretty sure that cigarette filter isn't cotton.

Maybe, maybe not....except I didn't actually post that. Not sure how that gets attributed to me.

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I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

Sorry, Stuart. That was a sloppy edit on my part. It's fixed now. Probably too late. The internet is already humming with the news that you finish your guitar with cigarette butts.

Tobacco sunburst.

Stuart, thanks. I keep hearing about polyester fills. I will study it. But not planning on a switch anytime soon. Maybe some test panels.

Brad, sorry I missed ur question. My process is fairly simple. It all depends on a perfectly pore filled surface. And a well sealed top. Assuming that, 3-4 light coats. If they are not light, they will flow too much. Lightly sand back some with 400-600. 3-4 heavier coats. Light sanding. Then 6 more heavy coats. As heavy as you dare. At this point you should be 7 hours in. You can do one more light sanding and a few more coats if you feel the need. I use an HVLP spray gun with 6 ounce cup. I'm happy if I get 1/3 of that on during a heavy coat without drips. Let the thing dry several days.

This stuff will raise the spruce grain (Enduro-Var). So I will do the top first with several coats. When I can sand top back flat, I'm ready for above schedule.

No powered sanding ever.

Stuart, you mention using urethanes that might even be better as a top coat. Could you name some? I tend to like the warmer ambers associated with urethanes. And, have you done this? If so is there a reliable schedule that you use?

Stuart, I'm quoting one of your comments above:

Point here....you can leave NASTY sanding swirls in the poly sanding sealer on BOTH the lacquer and poly topcoats. NASTY ones....150 grit blossoms....and you can't find a line to save your life on these test panels...or a guitar. This is the best indication I can give you as to whether you'll see witness lines sanding...but it certainly is optimistic for both lacquer and poly topcoats over this sanding sealer.

What I think you are saying is that you sand back to level, but do not worry about what the surface looks like in terms of sanding lines. And yet when you put the top coat on, they disappear. And the same appears to be true when you apply lacquer (nitro?) over that. Am I reading that correctly?

And, the poly sealer fully fills the pores with no shrink back?

Oh yeah....no shrink back whatsoever. It's stable once cured. Polyester has been used about as long as any plastic in commercial products. Think....boats....that's polyester gel-coat on the outside and that stuff is pretty close chemically to this stuff.

No...I have not done a guitar in urethane...just propellers. I did some test panels with urethanes but it came down to not wanting to develop an entirely new polishing schedule so I went for the polyester...because Simtec has one that uses the same finishing and sanding schedule as nitro.

I do, however, know generic aspects of how urethanes bond and (if the topcoat is not too brittle - and urethane car finishes are perfectly designed for micro-impacts...sand, pea gravel at 70 mph...ect.) in how they behave in abrasive environments. Urethanes are the perfect thing for little impacts and scratch resistance.

Here's what I know...Tony Ferguson: 616-842-4114...uses a PPG automotive product (I'm pretty sure). He told me specifically which one and I keep good notes but apparently I don't store them well because I can't find it now. Tony did three guitars for me early on....all stunning finishes. I'm sure he'd be happy to tell you which topcoat that was.

Yes...leave nasty swirls in the sanding sealer and then topcoat with either nitro or poly...no hint of the swirl after top coating.

_________________
I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

Well, I guess what I'm after is a great sealer that works on all wood surfaces (including the top), is water clear, pops the grain, and doesn't take all the time and effort of epoxy. Then, I can lay over that sealer/surface something like endurovar-var that gives me the warm tones I like. Sound like a dream?

I'm not being particularly careful about the thickness...I'm all electric over here....but I think this stuff could be put on VERY thinly after a bit of practice. The clarity of the topcoat is outstanding but I'm impressed with the clarity of the sanding sealer alone. I've leveled and polished test panels using JUST the sanding sealer and was impressed by the gloss, and clarity I achieved with it. Of course, you need the hardness of a topcoat but this test really brought out the character of the topcoat by itself.

On an acoustic I'd lay down a coat of sealer and then let it set up and then level it carefully. The next day I'd thin it even more and lay down another very thin coat....then follow up with one topcoat. I bet one could get it down to 1/3rd of the thickness that I'll do on an electric.

One thing that is particularly good about this stuff. Once you get the viscosity right it lays down easy, seals, AND fills without a hint of a trapped air bubble in any pore. Pretty amazing when you consider the learning curve that goes into each of those things doing it things other ways.

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I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

What kind of personal safety and exhaust do you use with product you are using, Stuart?

Alex

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"Indecision is the key to flexibility" .... Bumper sticker

I have a strong wall mount exhaust fan. I still use a respirator but I'd add that it isn't necessary.

I used polyester gel-coat in business years ago. In a closed room we sprayed small amounts of gel-coat (very similar to clear poly...catalyzes with the same MEKP...Methyl Ethyl Keytone Peroxide). We used more in one session than you'd ever use on a guitar. You'd think that was nasty stuff but the catalyst was used in such small quantities that the Washington State Dept of Labor and Industries set us up with a "voluntary respirator" program....essentially allowing the employees the option of wearing a respirator if they wanted. Two guys from the state spent a whole day in there with measuring equipment.

In a small, closed area I'd use one. Mine is a 3M 5301 with organic vapor filters.

_________________
I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

I can assure you it will bond over epoxy. I can also assure you it is not a good pore filler. It would take a long time to get enough on to do that. And even if you convince yourself the pores are filled, shrinkage will occur and expose them again.

I have to admit I am interested in doing some test panels. (pore fill). What brand "cheap" gun are you using? I'm not sure I want to run this through my good gun. And what cleans it up?

Interesting. I did not know that abut the KTM factory.

What I found worked best for me was to tint the actual finish rather than the wood. I used to use a very fine brush. I believe back in the day they recommended the foam brushes but I never had luck with that. If you heat the KTM in a water bath it helps it flow better too. I don't use water base anymore so I don't know what the SV means in the KTM-SV so perhaps it's changes a lot since I used it.

You are absolutly right though, screwing up KTM is indeed a nightmare, hence why I don't use it anymore.