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Epoxy fill vs polyester fill
http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10101&t=52899		 Page 1 of 1
Author:  Tai Fu [ Wed Feb 05, 2020 10:23 am ]
Post subject:  Epoxy fill vs polyester fill
I know many of you do epoxy fills, but I wonder has anyone done a polyester fill?

Epoxy fill works well except there are a few problems:

1. Epoxy is very sensitive to mix ratios, if they are wrong you get a mess that would never cure completely, resulting in a rubbery mixture that you can't get off and won't sand off.
2. Even when the epoxy is mixed properly and at the right mix ratios, the resulting coat while hard, seems to clog sandpaper like there's no tomorrow and still comes off rubbery.
3. I have found the particular brand of epoxy I use (I do not know who makes it, but it smells and handles and mixes like System 3 Epoxy) causes woods like purpleheart to turn VERY dark, like brown. I had to spray a coat of 2K over it in order to protect the wood prior to the epoxy fill. However I have found the 2K to fill fairly well but the epoxy fill still fills the minute binding gaps and making the whole guitar look flawless, assuming I put in enough elbow grease/sandpapers to get it sanded.

I found polyester tends to sand much better because it cures to a glassy, but rather chip prone coat that sands like a dream. I mean the kind of polyester resin used for fiberglass by the way. It can probably be thickened the same way as epoxy (using fumed silica) and applied in the same technique as an epoxy fill. Has anyone tried this? By keeping the polyester coat thin it would mitigate its tendency to chip...
Author:  Freeman [ Wed Feb 05, 2020 11:31 am ]
Post subject:  Re: Epoxy fill vs polyester fill
I use a Zpoxy, a finishing resin. I find it is not sensitive to mixing ratios, it cures very hard but seems to sand well, it does give a slightly amber cast which I like on most woods, and if I dilute it highly with DA it does a marvelous job of popping figure on highly figured wood that may not need pore filling (like maple). I have never used polyester, experimented a bit with CA but prefer the Zpoxy.

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Author:  Bryan Bear [ Wed Feb 05, 2020 11:36 am ]
Post subject:  Re: Epoxy fill vs polyester fill
Not all epoxies are the same so some of your complaints can be mitigated by the product you use. The only epoxy I have used for pore filling is Z-Poxy finishing resin. the Finishing resins are designed for this type of application not for gluing things together. I have found Z-Poxy to not be particularly finiky about mix ratio and sands beautifully.

I don't have any experience with polyester resins for any type of pore fill.

Edit: As I was typing, Freeman said everything I wanted to say only he worded it better. I know sourcing materials can be difficult for you in Taiwan. You may not be able to get Z-Poxy but look for a finishing resin epoxy and see if that doesn't help your issues.
Author:  mountain whimsy [ Wed Feb 05, 2020 12:11 pm ]
Post subject:  Re: Epoxy fill vs polyester fill
Many epoxies are very prone to "blushing", an almost oily residue left on the surface. I've found that is often what is gumming the sandpaper. It has to be washed off with a little soap and water before sanding. Or use an epoxy that is not prone to blush.
Author:  Tai Fu [ Wed Feb 05, 2020 12:20 pm ]
Post subject:  Re: Epoxy fill vs polyester fill
Yea, mine blush a lot. I can probably try washing but on something like acoustic guitar that can be difficult to do without damaging it. I try not to have water anywhere near it because I had bad experience with that.

The epoxy I use is intended to be used for fiberglass. I have not found any finishing resin. I buy mine resin from a chemical store that sells 1:1 (for gluing), 1:3, and 1:5. Mind you those epoxies are intended for their composite work or resin casting.

I thought about polyester resin simply because it tends to cure very hard and it is not too picky about mix ratios. Too little hardener just meant it cured slower.
Author:  B. Howard [ Thu Feb 06, 2020 7:07 am ]
Post subject:  Re: Epoxy fill vs polyester fill
I use polyester. I have used epoxy in the past and replaced it with polyester to eliminate the long open times and difficult sanding.

I used to use "hot" polyester pore fill which means chemically cured. It was better but when you considered the mess of spraying it and the fact it was very hard on guns I moved on from it quickly.

I now use UV cured polyester pore fill and love it. It is an easy to use gel, cures in minutes and sands easily without clogging up your paper. You can get an idea here....https://howardguitars.blogspot.com/2018 ... itars.html
Author:  Tai Fu [ Thu Feb 06, 2020 7:16 am ]
Post subject:  Re: Epoxy fill vs polyester fill
I don't think I want to try and spray polyester. I was intending to apply it with a squeegee like epoxy pore fill, and then sand it flat. Or perhaps brush it on. The resin is a bit thick to spray unless it's a gun with very large needles.
Author:  Mike OMelia [ Fri Feb 07, 2020 5:10 pm ]
Post subject:  Re: Epoxy fill vs polyester fill
B. Howard wrote:
I use polyester. I have used epoxy in the past and replaced it with polyester to eliminate the long open times and difficult sanding.

I used to use "hot" polyester pore fill which means chemically cured. It was better but when you considered the mess of spraying it and the fact it was very hard on guns I moved on from it quickly.

I now use UV cured polyester pore fill and love it. It is an easy to use gel, cures in minutes and sands easily without clogging up your paper. You can get an idea here....https://howardguitars.blogspot.com/2018 ... itars.html


I have studied your work on this Brian. And I would love to do (and might still do) this. It seems to me the cost of of admission (UV curing lights etc) keeps a lot of folks out. Wish this was not the case. I would def be interested in your thoughts on how the cost could be brought down.

Mike
Author:  dzsmith [ Fri Feb 07, 2020 7:11 pm ]
Post subject:  Re: Epoxy fill vs polyester fill
+3 on Zpoxy.
It does not require precise measuring when mixing and it dries hard, and fairly easy to sand.
Author:  Mike OMelia [ Sat Feb 08, 2020 4:44 pm ]
Post subject:  Re: Epoxy fill vs polyester fill
I totally agree on zpoxy. So easy to use. I also use west systems when I don’t want an amber pop (but west does require more precise measurements)
Author:  Tim Mullin [ Sat Feb 08, 2020 5:04 pm ]
Post subject:  Epoxy fill vs polyester fill
While I agree with all the positives cited for Zpoxy, my experience (2 different kits) was it led to (1) pore shrinkage in Indian rosewood within a year or so, and (2) some amine blush. While this is reported by others, most users swear by it.

I took Joe White’s recommendation and switched to West System 205/207 and never looked back (precision measure using glass syringes, cleaned afterwards in DNA).

I agree with Brian that a better choice is UV poly. It does of course require a significant investment for application and safety. I made the move this year to contract out my finish work to Vancouver Guitar Finishing who use Simtek UV poly as their default pore filler.


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Author:  B. Howard [ Sun Feb 09, 2020 8:00 am ]
Post subject:  Re: Epoxy fill vs polyester fill
Mike OMelia wrote:
B. Howard wrote:
I use polyester. I have used epoxy in the past and replaced it with polyester to eliminate the long open times and difficult sanding.

I used to use "hot" polyester pore fill which means chemically cured. It was better but when you considered the mess of spraying it and the fact it was very hard on guns I moved on from it quickly.

I now use UV cured polyester pore fill and love it. It is an easy to use gel, cures in minutes and sands easily without clogging up your paper. You can get an idea here....https://howardguitars.blogspot.com/2018 ... itars.html


I have studied your work on this Brian. And I would love to do (and might still do) this. It seems to me the cost of of admission (UV curing lights etc) keeps a lot of folks out. Wish this was not the case. I would def be interested in your thoughts on how the cost could be brought down.

Mike


It is a somewhat expensive system.... But how much did you spend on some of your other equipment like band saw, joiner or maybe even CNC? Just another investment.

The question you should ask is how valuable is your time? Sanding back polyester filler versus epoxy will save you about 25% on your time and materials costs for that step of the process, sandpaper savings themselves add up quickly. The material while seemingly expensive is really quite economical as 1 quart of UV gel filler does dozens of guitars and has no real expiration date as long as it is kept cool and in the dark. And the fact that your shop is available for dusty work in the interim as needed without waiting hours for epoxy to cure... that's priceless in a small shop without dedicated finish room capabilities.
Author:  Tai Fu [ Sun Feb 09, 2020 8:14 am ]
Post subject:  Re: Epoxy fill vs polyester fill
So what's wrong with using conventional polyester cured with MEKP?

Sure it doesn't have the readiness of UV system but it doesn't have any lamp cost. Maybe if spraying it is a problem perhaps brush it on the same way you brush on epoxy? Consider it's so much easier to sand means you'd use less sandpaper, take less time, etc.

You could lay on a somewhat thick coat (for solid body electrics) and just sand it off with 220 grit random orbital sander.

I started using 2K finish because instead of waiting 2 months for the finish to maybe cure (it doesn't always cure enough for polish) and have an inferior finish that checks, crazes, yellows, etc. over time (not to mention shrink over time too), 1 quart of 2K can do several guitars, cures fully in 3 days TOPS, and is UV resistant, doesn't yellow, the finish is hard as a rock. I can finish a guitar in a week instead of 2 months. 2K costs more but I think it's worth it... The finish I use is a Japanese brand called NAX, it is what Ford motors use in Taiwan for their cars... Being able to buff at high speed and get incredible shine is a plus too (with nitro I have to be more careful because it's softer).
Author:  B. Howard [ Mon Feb 10, 2020 7:52 am ]
Post subject:  Re: Epoxy fill vs polyester fill
Tai Fu wrote:
So what's wrong with using conventional polyester cured with MEKP?


Nothing.... I did it for about 18 months....

But I can tell you have never really messed with the stuff. It is thin and incredibly sticky so it will not spread well. In fact trying to squeegee it I think will guarantee air bubbles trapped at the bottom of the pores. It also attracts a good bit of dust from the atmosphere as it cures, you'll be surprised at how much it grabs in 30-40 minutes before it skins up. And even spraying coats that had as many runs as a river still requires 2-3 coats to get a good level fill on something like mahogany due to high surface tensions preventing good flow into the pores.

But hey, give it a shot. But again if you want fast cures of every stage of finish UV does that. I don't even like 2K urethane anymore.
Author:  bcombs510 [ Mon Feb 10, 2020 10:30 am ]
Post subject:  Re: Epoxy fill vs polyester fill
While I haven't done a ton of instruments with it yet, I have to agree with Brian it's pretty great to be able to do 2-3 coats of pore fill in a couple hours after work. :)
Author:  B. Howard [ Mon Feb 10, 2020 10:52 am ]
Post subject:  Re: Epoxy fill vs polyester fill
One thing I forgot about MEK cured poly..... The sealing wax makes it eat up sandpaper like no ones business!

What is sealing wax? I know that's next..... The difference between laminating resin and finishing resin is a wax that is added. To completely cure this material must be kept oxygen free. Otherwise the surface stays tacky which can be useful when laminating. This stuff ate more sandpaper than anything else I ever used. I suppose you could remove the wax with solvents prior to sanding but you risk compromising intercoat bonds I think in some systems.

And not all resins are created equal. Varying amounts of styrene as just one example will yield very different resins both wet and cured. Pick one too hard or soft and.... well I think you know.
Author:  Mike OMelia [ Mon Feb 10, 2020 6:04 pm ]
Post subject:  Re: Epoxy fill vs polyester fill
Brian, that Isolante from Simtech. You ever figure a way of extending the resin shelf life? Was thinking of trying Blox. (some kind of inert gas mixture)

Mike
Author:  B. Howard [ Tue Feb 11, 2020 7:03 am ]
Post subject:  Re: Epoxy fill vs polyester fill
Mike OMelia wrote:
Brian, that Isolante from Simtech. You ever figure a way of extending the resin shelf life? Was thinking of trying Blox. (some kind of inert gas mixture)

Mike


IME BLOX shortened the shelf life of these products. Keep the activator container meticulously clean. Any spec of dried hardener that falls back into the fresh materials can kick off the whole can pretty quick.
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