Keep, hold for image processing: Experience with Polyester finishes [Pictures] - created 07-25-2005

Arnest, Bernard - 07/25/2005.15:42:10

Hi,

Now, Mario said that there are some that WILL let you buff the next day? Which specific finishes are they? And would you recommend trying them?

Alternatively, even if I can't buff, can I leave the guitars hanging for a weeks for the nitro to cure, go to college, and then buff them another week or so later? Or, in taking them in their cases to college, will it damage the finish, leaving imprints from the cases; and so if I still use nitro I will have to leave them at home and buff them thanksgiving break.

thanks!

-Bernard

Polyester -can- be done at home. If your home has a spray booth, you have the protective equipment to keep yourself alive, and no neighbors close enough to complain of the smell.

McFadden's polyester can be cured via one of two methods: we can add a UV initiator, but then we need a strong UV source. This is what the Taylors and Larrivees and other large shops do. Cures in seconds! But the UV source is expensive, and eats power, big power.

The same polyester can also be cured via a chemical process, using Cobalt drier, and MEKP. McFadden's will supply the Cobalt, but you have to find your own MEKP. You'll also need MEK to thin it. Fully cured in 3 days, but I, and others, have sanded and buffed within 24 hours, and the results have held up fine!

Under either one, you'll need to use a special sealer, along with its own hardener.

Oh, and then you'll need a couple gallons of acetone in a sealed pail for your gun to live in, as it will never be truly clean again.

There's a steep learning curve with it, one that cost me dearly, as I had to re-do 12 guitar bodies this past May

Not for the faint of heart, and not for a student who will build one instrument here, and one there. The stuff is expensive, has a rather short shelf life, and I am not aware of anyone selling it in less than 5 gallon quantities.

But it is an amazing material! Cures fast! 90% solids. Repeat, 90% solids! What you put on, stays on; it does not all evaporate . It sprays oh-so beautifully, and I swear, if it wasn't for dust bumps, I could spray this stuff on, and not have to level and buff afterwards. It sands like nothing you've ever sanded; it does not clog papers at all. It is tough to buff, and requires quite a learning curve in that respect, also, but once buffed out to what it can be, it is beyond even nitro in clarity and depth, and it 'wets' the wood as well as epoxy, shellac, or any oil ever could. It is also its own pore filler(did I mention 90% solids?). 3 coats are enough. Yes, 3, and sprayed 45 minutes apart.

Downside? Stinks. Dangerous. Expensive. Stinks. Dangerous. Hard to buff. Stinks. Dangerous. Hard to repair. Stinks....

As for tone, it does have the worst reputation as a tone killer, doesn't it? But thinking back, where do we always see it? Inexpensive Asian instruments, where they butter the stuff on in thick layers. It also has a strange ability to build at corners and edges, unlike nitro and waterbornes that flow away from edges and corners, so it looks even thicker than it is.

I went ahead and tried it on a guitar that had lived with a nitro finish for nearly a year. Stripped the nitro off, and shot the polyester. Reassembled it, and if anything, she sounds better, more open. But, my final measured thickness, at the bridge, was a tad under .003", likely 5 times less than what we'd find on factory instruments using this stuff, and even thinner than my nitro finish. I've since measured each one of the guitars I've done in it, and none have had over .005". Yes, I've cut through, on at least half the guitars, so far, and yes, it's a bear to fix(basically, re-do the entire plate that was cut through...), but I'm getting better at judging how thin I'm getting. Thing is, it is so clear, that this is tricky to do, and a big part of the learning curve. It is also, I'm sure, why factories slap it on so heavy.

so, did I discourage everyone? Inspire anyone? If anyone wants to seriously follow through with heading towards trying it, I'll go further with part numbers, and actual mix ratios, and maybe a trick or two I've learned, so far. I'm still learning, too, but I have a firm enough grasp of it now.

Hey, Mario, after I ran into it on a cheap import I tried to refinish (applied in heavy, heavy gobs as you mention), I'd dismissed it as unusable for quality instruments, but what you are saying is that it may actually be good stuff! So, I'm more curious now :)... and have questions...

I think you allude to this, but I've read that some of the really fast curing stuff can be so fast as to solidify in the gun within 15 minutes... is this what you mean about keeping the tips/gun submerged in acetone?

What nozzle size/pressure are required to spray?

Is it a two part substance?

You say it stinks to high heaven, but is it explosive like nitro?

What brands have you been using (just McFaddens?)?

Did I read that right? No pore filler or even a sealer coat?

I think that's it for my questions for now :). I have read a lot of what you mention about it not being for the faint of heart... and I'm guessing it requires super-strict regiment? Still... the results seem like they might be worth it. Oh, isn't this a common piano coating?

help me out here,

my knowledge of two part polyester finish comes from watching some one do a piano.

I love the finish but I know I'm not ready to live with the fumes in my shop. The smell reminded me of the stuff we put on surfboards and some of the poly fillers I've used for molds. Yet Taylor is saying that one of their main objectives was to get rid of the smell. When you guys visited Taylor , was the smell there. Are you spraying the same stuff , just not uv cure or do they have something different? In lacquer the smell is volatile compounds , do we know what it is in poly. Thanks if you can give me some clarification.

so fast as to solidify in the gun within 15 minutes... is this what you mean about keeping the tips/gun submerged in acetone?

Yup.

What nozzle size/pressure are required

1mm, whatever pressure your gun wants.

Is it a two part substance?

3 part, 4 of you count the required MEK thinner.

stinks to high heaven, but is it explosive like nitro?

Stinks? Did I mention it stinks... Yes, explosive, too.

brands have you

Just McFaddens.

Did I read that right? No pore filler or even a sealer coat?

No, you didn't read right. There's also a 2 part sealer required. Yes, it acts as its own filler, or you can still use a paste if you wish.

guessing it requires super-strict regiment?

Very. To the tune where you need a timer and bells to make sure you get back in there and shoot the next coat on time, or else....

Oh, isn't this a common piano coating?

No idea. I don't build pianos....

I'm not ready to live with the fumes in my shop

As well you shouldn't. What was my first line? " If your home has a spray booth"

There, that says it all. This stuff isn't for spraying in your shop, it's for spraying in your booth. That said, the stink only lasts about 12 hours, and absolutely all off-gassing is done in under 24 hours. This for me was the biggie. I can protect myself to the nines while shooting, but nitro keeps off-gassing for weeks, so there was no way for me to get away from it. This stuff, I can shoot in the late afternoon, and the next morning, hit the fan to clear the shop and booth, and that's all she wrote; no odors after that. I'm in the process of setting up a postive pressure face mask outfit to shoot with; that should give you an idea of how nasty and serious it is.

When you guys visited Taylor , was the smell there. Are you spraying the same stuff

I've never visited, but I'm positive that they're spray room(s) are well ventilated and kept separate from the rest of the place(if the spraying isn't fully robotic already; the buffing is...). Being 90% solids, there are very little VOC's compared to nitro, but those that are there are nasty. The MSDS sheets make nitro look like orange juice . I'm told by those who know that we're using the same product and part numbers, except for the methods of curing.

Listen, I do think this stuff has a place with the small builder, because it has so many positives, but it requires some serious equipment and respect, as well as some time to get used to it and make it work. You're not going to use it in your basement "shops", and you're not going to shoot it outside with the dust and bugs, as it stays tacky for an hour or more, thus attracting bugs and dust. For the serious builders among us(mostly lurking: hi guys and gals!) with the stuff to take advantage of it, and use it safely, it has no equal.

Thanks for the clarifications, Mario! It sounds like it's not at all for me for now, but it's good to know about because someday I may be better prepared for its challenges and more in need of its advantages and then I'll take a second look. That said, it seems some others are also reading this discussion for whom it might be more viable, with some effort.

thanks again!

-Bernard

You're welcome, Bernard. Yes, I completely understand that for most here, it is not the right finish, but I'll bet many(mostly the lurkers I aluded to) will be surprised to see that it could be for them, too. I wasn't aware that the stuff could be used without the expensive and complexe UV systems, and when it was pointed out to me(about 18 months ago), it was an eye opener, so I'm more than willing to let the cat out of the bag, so to speak, by letting it be known that this can be used by more of us than we would think. And again, this in no way hurt the tone and power of my guitars; every one that I've completed this year has been as good or better than any I've ever done; only much prettier! I've had to eat much crow on this subject...

Here's one I buffed recently: cocobolo(thanks, Larry!) and ebony bindings, under fluorescent lights. If there's a combination that will show the shortcomings of a finish, this would be it, yet look at the clarity and gloss, and again, no pore filler was used.

Here's the same guitar's neck, straight from the gun, without buffing.

Same neck, again, no levelling, no buffing, yet. Note in this photo, and the previous one, that the finish is heaviest at the edge and around the holes! To anyone who's buffed-through at an edge, this is lovely to see

WOW! That's just wild! Heck, I wish some of my finishes looked that good AFTER buffing (very sad, isn't it....).

I was doing some reading on the stuff last night and polyester is in fact a mainstay for high end pianos, if not for the entire finish, for at least some portion of it. Based on the way that looks in your photos and its reputation for indestructability (witnessed first hand by many of us), I can see why.

I was reading that some piano-finishing methods use polyester as a base and then they shoot a few layers of nitro-lacquer over the top of that to aid in future repairability. I wonder if that's actually useful and if it would be something to consider on guitars, which have the potential to see more abuse.

Nitro over polyester is done by many guitar makers already, for its repairability. In one case where I had to do a repair after the fact, that is what I did(over sprayed an entire top), too, and it works great(if you can handle the nitro...).

Mario... Thanks for the update... a very interesting post. During the learning curve... what types of problems were you having? Chemistry or technique? I like the look and so thin...wow. I always feel like I'm slowly killing the instrument with each new nitro build coat. But the idea of learning on my next 12 instruments.... hmm, I don't like the math.

Chemistry or technique?

Both. The chemistry is touchy, and I needed to get a pair of syringes to be able to measure the cobalt and MEKP accurately enough. But it was the sealer that gave me the most fits...

Technique meant tossing my old, cheap guns, and investing in a way better unit, with a pressure gauge and regulator at the gun, and also finding an air drier. Then there was the sealer.......

The big problem that saw me re-doing a month's spraying and levelling was a sealer miscalculation, causing an adhesion problem(one ding, and the top coats would peel off!). Arghhh! But that's behind me now, too.

Mario, It sounds like you are where I want to be with the conversion from nitro to polyester. I've been reading about this stuff on a few forums and although your problems aren't exactly encouraging me it is good to hear that there is light at the end of the tunnel. I bought a gallon of McFadden's to test out but it didn't come with anything except safety info. I'm curious to hear about your wash mix ratio, your spray booth conditions (temp and rel humidity), and gun cleaning. I'm also curious if you had to upgrade your booth at all to work with this stuff. I have a spray "room" now that is connected to my shop that has been working well for nitro (sealed lights, sealed door, explosion proof exhaust fan with intake and exhaust filters) but everyone makes polyester sound so horrible. Is the smell/gases that much worse than nitro? I see that it is gassing off for a shorter amount of time, but is that short time more concentrated?

Do you have any reference to read up more on this stuff? I've looked online for some generic info on this (not necessarily musical instruments) but I've turned up dry. Thanks for any info and for what you've posted already. I'm looking forward to making the switch so this thread is a real help.

One more thing! Do you have suggestions where to find MEKP? I asked for it at the local paint shop and they gave me MEK, I had a feeling it was the wrong thing since it didn't say peroxide anywhere on it.

Well, if McFadden's sold you some, then they'll also answer your questions. Just ask for the tech guys. They're the ones who will help most, just keep in mind that they tend to talk of mixing gallons at a time and using it up right then and there . They get a little lost when you tell them you only need to shoot 3oz at a time.

In short...

0.4cc of cobalt per 1oz of polyester. Mix well, let sit for minimum of 15 minutes before proceeding. Next comes 0.6cc of MEKP per 1oz of polyester. Mix well, very well. Add enough MEK to thin it to work with your gun, booth temp, etc.... About 10-20% works for me. Strain completely as yuo pour to your gun. Enjoy!

Mcfadden's rosewood sealer comes with its own hardener, used at 10% hardener/volume. It's a very good idea to use this sealer on everything, and not only rosewood. It's water thin, and wets the wood beautifully, so it doesn't hamper anything, but it reminds me a lot of nitro in its smell...

Your booth sounds like it will be okay, but you'll want to upgrade, or at least check, your respirator cartridges; take the MSDS sheets to your safety supply place, and they'll fix you up. Or, better yet, invest a few grand into a full face, pressurized system. Stuff is nasty... Temperature is not too important, but it won't cure below 60f, and cures noticably faster at about 75. But it's pretty forgiving; I've played around with keeping my gun's cup on ice in between coats, to see if I could mix all the junk in one shot(the smaller the numbers, the harder it is to get the mix ratios just right, and 3oz is all you need to do a coat on two guitars, so mixing 9-12 oz would be better).

MEKP is availbale from any fiberglass supply place. Any auto parts place will have little tubes of it, but those who supply serious fiberglassing places will have it in pints and quarts. Google be your friend...MEK, as you noted, is available from many paint shops. Cobalt is available from McFaddens.

Is the smell/gases that much worse than nitro?

Gases are less so, I find, but the smell, when spraying, is heavy, and lingers. And bitter. Ever work with fiberglass resins? Imagine spraying them....

Mario,

your work looks great. I always assumed polyester was work of the finishing specialist only rather than the lone builder. It definitely is a science , but you make it sound doable.

Though because I'm already beginning to get reactions to lacquer fumes, I think I'll wait for the water base system ..ha ha.

Still curious about Taylor's claims.

The reason I am using this is because I've been terribly allergic to nitro since late '99..... No problems with this stuff.

What are Taylor's claims?

For anyone who's interested, I've found SimTec Coatings (obvious URL) also sells a polyester system that they claim works well on exotic woods and instruments. They sent me a catalog of sorts and in the catalog, they give you little tables to aid in the mixing of small quantities of product (like how many drops/cc/mls/grams of catalyst to add, etc.).

In regards to spray conditions: somewhere (can't remember whether it was McFadden's, SimTec, or Ilva information), I read that that a particular polyester product should be sprayed when it's BETWEEN 50-85% ambient humidity... That seems weird and I'm wondering, Mario, had you had any trouble with it being to DRY to spray? I can't find that info anymore and am hoping it was for a very specific product.

Also, about the spray gun: Mario, you mentioned you tossed your old guns for a better gun. May I ask why and what you went with? Was it atomoization issues, or was it the regulators and adjustability on the better gun? Also, what do you clean with (flush with, say, acetone or something, or power gun washer)? The thought of having the stuff harden in and ruin a top-of-line SATA gives me the willies ;>.

Thanks, Mario, for taking the time with these questions.

any trouble with it being to DRY to spray?

Nah, not so far.

you tossed your old guns

Firing pin stayed stuck just as the bear approached....

Oh, the spray guns?

Trying to keep the total build as thin as possible, I felt I needed to lay down as smooth a coat as possible, instead of the grainy finish I was getting. I never did worry about this with nitro or waterbornes, as I could touch up any tiny imperfections or buff-throughs easily, but not so with this stuff. I also felt I needed to reduce the overspray, as the stuff is nasty. Did I mention nasty yet? HVLP was in order, So....

Wrote around to those who know much more than I, and asked for recommendations. The Mini Sata was always near the top, but surprisingly, so was the DeVILBISS SRi series, specifically, the SRi-630G-10. I was told it would lay a coat on as nicely as the Sata, but when the time came for replacement parts, especially the cap and needle, the Sata's prices were 8-10 times higher. So, while they cost the same up front, in the long run, the DeVILBISS should prove more economical, and, big one here, it was available nearby.

As the photos show, it lays the stuff down nicely, don' it? I've never been more satisfied with a tool purchase. It does everything I was told it would, and then some.

Clean the gun with MEK or acetone, MEK being cheaper up here. Once polyester has been in the gun, you'll never use it for anything else, so be aware of that.

I thought I would point out that there are a few choices available with MEKP. Some are intended to be used for temperature adjustments during the winter, some during the summer. I used to use Witco Hi-Point 90 during the winter. One word of caution, keep the cobalt away from the MEKP. There is a violent reaction if they come in contact with each other! Also there are inhibitors for a slower cure and promoters for a faster cure in polyesters. Nice work Mario, maybe some people will start believing me about the properties of polyesters.

that there are a few choices available with MEKP

I asked the tech guys at McFaddens about this, and they said to not worry about it, that any MEKP would do. I think that the various MEKP formulation are more important when used with casting polyesters, where castings of over 3/4" can cause a lot of heat.

I think....

Thanks for the reminder of the cobalt VS MEKP reaction! Yes, that is a potentially nasty one(there's that -nasty- word again...). I believe this is why we're told to mix the cobalt in, and set it aside for 15 minutes or more.

Taylor claims that in his exterior finish there are “ virtually no solvents.... because... a blend of monomers and oligomers.”

And your saying “Being 90% solids, there are very little VOC's “.

My understanding is that VOC’s are the byproduct of evaporating solvents. So am I to understand that there are solvents but just a lot less (10% or virtually ‘few’) And that your in agreement with Taylor . Or by formulating for uv Taylor has less solvents. Or are the VOC perhaps just out gassing of the chemical reaction?

Have you thought of applying UV .I read they had to work with many companies to arrive at a workable product.

I’ve built a uv box for violin varnish and I’ve seen a few other functional , inexpensive , low tech versions in colleagues shops. I wonder if Taylor is using something that is beyond the small shop. The picture in the article I read is definitely reminiscent of the master cylinder of Felix the Cat era.

Because artificial UV has worked well for me I have a bit of interest in it.

I as well have a curiosity in the various UV adhesives and sealers used in the dental trade and there potential for repair work.

Again thank you for your clarity.

You're reading too much into everything.

Yes, 90% solids means very few solvents will evaporate. In contrast, nitro is around 22% solids. That means for every gallon sprayed, 10% of the polyester goes to the atmosphere, while 78% of the nitro goes up. See?

Have you thought of applying UV

No, because the UV needed is beyond what you or I can use and/or control. This is not your little UV cabinet with the little lightbulbs. This is very strong light, creating an awful lot of heat, enough so that a huge air conditioner is required to keep a blanket of ice cold air flowing between the instrument's body and the light source. We're talking Kilowatts. We're talking a UV source strong enough that people cannot be present. Get the drift?

There are smaller, hand-held lights that only cost a few thousand bucks(!!!!), but the operator still needs a full suit to protect himself while he carefully waives the light over the instrument, and since the light isn't quite full strength, the cure still takes hours.

What we're discussing is a chemical cure system where full cure is acheived in a few more hours. No expensive lights, no dangers, no nothing. Just a few extra hours to full cure. It's the only thing that makes sense unless you are trying to finish a few hundred guitars per day, at which point, you would not be asking _me_ for advice

Listen, save yourself the hardship, and forget everything you've read about at Taylor. They are a huge outfit, and very little that works for them, will work for you. Be realistic.

"You're reading too much into everything........very little that works for them, will work for you. Be realistic."

My original interest with Taylor was their results and the environmental recognition they have received. I appreciate the time you have given here,and thank you for answering my questions. I personally have a preference for french polish and oil varnish, But as I teach a general wood finishing class ,I feel a responsibility to keep current. Your techniques and practices are very well understood in the piano finishing trade. However to spell this all out for guitar makers is a welcome gift to this forum. Thank you again.

"I think...."

Thats pretty much it. Heat or lack of it is the reason to change the catalyst. I assume you keep the guitars at the room temperature, if they were a little cold the cure would be slower. Because the finish is fairly thin, exothermic heat from the film thickness would not be a problem. The only time to change is when you are not getting cure times you can live with. And then only with the tech support guidelines. Polyester can become brittle and worthless with over-promotion. And yes, I learned this the hard way. They do offer a lovely shade of red tinted MEKP, I have used it many times and find the color pleasing.

"cobalt VS MEKP"

I guy I used to work with cleared the shop when people realized he was pouring cobalt and DMA into the polyester resin at the same time! I can only assume that the cobalt and MEKP reaction is a doozy, I sure have never done it! I have always mixed promoters one at a time, completely.

I think if I wanted a faster cure I would try the IR lamps rather than the UV. I remember the IR lamps were very reasonable, the most inexpensive around 600 usd. That was over ten years ago, so the price may have gone up or down.

Hi.

I have a question???

What about repairability in polyester?

Would it leave a tell tail?

Yes, thanks for sharing, Mario.

After reading this thread, my new formula is almost complete:

" sqrt[(length + enthusiasm in Mario's messages)/ # coffees - # instruments-refinished-last-month + # of bears missed * 0.04MEKP] ~= # daylight hours at latitude 46 degrees north."

What about repairability

Well, that is relative. first thing you must do is forget every repair technique you know of.... Almost.

As you're working with it, if you see a gap that needs filling, you can do a drop fill in between coats, and that will be invisible.

When cured, drop fills do no more than fill the dent/hole, as they will not burn-in. If you try to spot spray an area, it will not blend.

What I decided was simplest is to re-finish the entire plate. If there's something to repair on the back, sand the back down level, and take it down to nearly wood, mask off the sides, and shoot it with 3 new coats. It will blend seamlessly at the binding edges. Same for the top, the neck, headplate, and same for the sides. From the time the damage was discovered, to final buff and back to 100% repaired is under 24 hrs. if you need it to be. Try that with WB or nitro!

Seems like a lot of bother for what is often small damage, but, really, it's turning out to be much simpler. For example, a month ago, I was just about ready to box up a new guitar, but decided to buff the string nut a bit more(after re-crowning it). Took the strings off, and made a nice, deep scratch in the headplate! Arghhhh! Had this been nitro, I would have done a drop-fill, and called my client to tell him his guitar would be two weeks late. Two weeks later, I would have levelled the drop fill, sanded and buffed out the headplate, and hoped that there would be no more sinking(doubtful...).

In this case, I didn't hesitate one bit; I pulled the tuners off, scraped the finish down level on the headplate in about 5 minutes with a razor blade, masked off the rest of the neck, tossed a towel on the guitar's body, and shot two really wet, thick coats on the headplate. Turned the heat up in the shop to about 80, and went to bed. About 16 hours later, I levelled it and buffed it out, reinstalled the tuners and strings(and buffed the damned nut!), and boxed her up. Client got it in time, and I'm positive the finish will not sink or go ugly.

So, it's all relative. At first, I was really lost as to what to do with the inevitable bench dings that will happen sooner or later, but soon realized that it takes so little time to re-do a whole plate that that would be the repair of choice. Thinking back to nitro, it really isn't as repairable as we make it out to be. Repairs take forever to cure, then they want to shrink back forever. They only look invisible for a year or so, then show up as little ghosts half the time.

As for repairing completed guitars, there are techniques available, but, in 9 years, I've nevre once been asked to repair a ding or scratch in one of my guitars, so I'm not even worried about that part of it. Sure, there will someday be someone who freaks over the first ding and wants it fixed, but these customers are few and far between, methinks. For these guys, if it must look new again, we can either, again, re-do the plate, or top coat it with nitro(still debating which would be easier..)

Henry, if I seem enthusiastic, it's because I am! Nitro became a no-go for me nearly 6 years ago for health reasons(it tries to kill me via "chemical asthma"...), and nearly ended this career. Having someone else shoot my stuff sucked(both time-wise and quality), and the waterborne trail, while it continues to make big gains, isn't ready. Everything I've tried had problems, and even the latest ones, that I thought would be tough and safe, softened and went bad under at least one person's hand a year or so later. Stuff just ain't ready. And nothing, not even nitro, looks like this stuff. I now bow towards California at the end of each day, and silently thank Rick Turner for his help and advice with this stuff . I'm not passing on new knowledge; I'm merely pasing on what was passed on to me.

>I'm not passing on new knowledge; I'm merely pasing on what was passed on to me.

It is hard to imagine how anyone could have done a better job of passing it on. Many thanks for taking the time.

and even the latest ones, that I thought would be tough and safe, softened and went bad under at least one person's hand a year or so later

I'm discovering this same thing with a guitar I finished with KTM-9 a year ago. Disappointing for sure.

Hi guys.

Mario, thank you very much for the info.

But is this the same kind of polyester resin that is used for fiber-glass,

like ASHLAND/CHEMICAL brand?

That's the only thing I cand find in this country of mine that can help me achive achieveype of finish.

(Sorry, I'm not Mario but...)Omar, what country are you in?

Hi Ryan. I live in the Dominican Republic. Right in the middle of the caribbean.

Omar, while they are very similar, fiberglass resin isn't quite the same. Fiberglass resin needs to cure hard, while the polyester finish needs to be able to flex readily. I'd also imagine that the finish is finer, while the fiberglass resins are coarser(just a rough observation...).

You _can_ give it a try, but I can't promise results at all.

Thanks Mario.

I'll give it a try to see what i can come up with.

If i don't like it , I might switch to UV currable finish.

Do you know something about it?

"You _can_ give it a try, but I can't promise results at all."

Mario is right. Be prepared to pay your dues, He had to!

"kind of polyester resin that is used for fiber-glass"

A few things jump out as differences. The cure of most polyester resins are inhibited by contact with air. In other words, the outside surfaces will be sticky and hard to sand. They require surfacing additives to fully harden. The layers underneath the outside are no problem. Also most polyesters are much thicker to make fabricating parts less of a problem. Imagine all the resin bleeding out of the fiberglass cloth or matt onto the floor and you can see the problem. No normal polyester resin I have ever seen would be suitable for acoustic guitar finishing.

This McFadden polyester finish is obviously a specially formulated type, like nothing I have ever seen. In twenty years I have seen everything from fire retardant resin to sanitary/medical approved types. My congratulations to the guys at McFadden's! I guess I have something new to use when I build an acoustic.