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Anyone do this? I'm using System3, and sanding it is driving me mad. Out of frustration, I took a freshly sharpened scraper to it, and it seemed to do a nice job of taking the bulk of the residue off. At least to the point where I don't have to waste many sheets of sandpaper to work it down to bare wood.

Is there a horrid downside to this? My sandpaper loads up almost immediately with little dots of epoxy, rendering it useless, at least till I flick them all off with a fingernail, which seems like an exercise in futility.

Also, after 48 hrs, the epoxy is no longer tacky, but if I hold it barehanded for ten seconds, there is a slight stickiness to it. Is this normal, or should it be utterly un-sticky? Would a tad more hardener help? I'm guessing this is the cause of the little dots of it on my sandpaper, or does this happen regardless? Any thoughts or suggestions are appreciated. What a pain!

Ken

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Mountain Song Guitars www.mountainsongguitars.com

Ken check your mix ratio and/or age of the System III.

System III sands very well with minimal loading but it is SUPER sensitive to the mix ratio and a gram scale is a "must have/use" for working with System III.

System III also cryptically indicates on their web site that it only keeps about a year and breaks down with UV light so keep it in the dark.

I thought of using this stuff but there seems to be a steep learning curve to using this stuff and the zpoxy stuff. I have read about other peoples problems with this stuff on other forums. I think I will stick with the pore-o-pac stuff. I have used this on woodworking projects with no problem.

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Guitars, guitars and more guitars.

Pore filling with epoxy finishing resin (not run of the mill epoxy that can be old...) is a piece of cake.

Loading is symptomatic of the epoxy not being cured properly and System III is known to me mix ratio sensitive (see LMI's site and notes on SIII use).  It is however excellent pore filler if mixed as per the instructions.

Z-Poxy "finishing resin" is my current favorite, very easy to use, not mix ratio sensitive, and widely available many places.

Some use West Systems as well and report excellent results.

Hesh --

I've had it since March, and have kept it in my flammables cabinet. I'm using a digital scalethat reads in grams, but not tenths, which may be the problem. I used Mike Doolin's ratio on the LMI site of 100:44. Since I only mixed ten grams of A, I had to estimate the last .4 gram. I'm confident I was within .3 gram either way, though that may be enough of a discrepancy to account for the problem.

For the next coat I'll use an even 5 grams and see if that helps. What is the downside of using slightly too much hardener?

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Mountain Song Guitars www.mountainsongguitars.com

Ken it sounds like you nailed the mix ratio and were/are following the instructions precisely.  My apologies if I came across as if you didn't.

A couple more questions for you if I may please. 

Did you by chance put down a seal coat of shellac prior to using the System III?  Shellac sticks well to cured epoxy but epoxy will not stick well to cured shellac.  Just want to eliminate this one before moving on.

What is the wood that you are pore filling?

Although March is not a year old yet we buy our products from distributors and there may be a question as to how long they had it.

I would not try increasing the hardener since your mix ratios have been correct.  Instead I would pick up some Z-Poxy finishing resin (available at Wood Craft) and try that.

My experiences with S III were all very good and it sanded into a fine dust and did not load up the paper.  I used 3M fire-cut 220 grit paper.

For small quantities, it really does work well to mix by volume (as recommended by System Three) using syringes to measure, but I guess if you want to use your digital balance, that's your call.

I haven't used a lot of System Three epoxy- about 10 gallons over the years- but I did find that it tended to develop amine blush quite easily- this is a 'greasy' film on the surface, which can be washed off with soapy water and a Scotchbrite pad. Blush will definitely lead to loading up your sandpaper.


Thorough mixing is a must, of course, and failure here will lead to partially-cured/sticky areas in your work- this is particularly a problem with small quantities of epoxy. Sometimes mixing in a Ziploc bag can help- many mixing containers have 'corners' and grooves which can prevent complete mixing.

Epoxy films don't reach their final 'hardness' for weeks; sometimes an extra day in a warm area can improve the sanding properties a lot.

Shelf life on most epoxies is excellent- I wouldn't hesitate to use epoxy that was several (5+) years old.

I recall (dimly) that the Gougeon Bros found that hydrocarbon fumes(?) from a portable heater kept the epoxy on one of their boat projects from curing, so you might think twice about storing your epoxy with your solvents, unless it's required by your fire department.

If you need to do a 'lot' of sanding, you are probably putting the epoxy film on too thick, so that's something to keep in mind as well.

I wouldn't bother switching epoxy brands, but it might be a good idea to do some trial mixes before putting any more on a guitar. I did find out (the hard way) that the 'waste' of trials and tests with expensive epoxy was small compared to the aggravation of cleaning up problems I could have avoided.

Good luck with it! Epoxy is one of the easier steps in finishing, in my experience.

Cheers
John

I forgot to mention that excess hardener (or resin) in the mix will lead to soft epoxy and lots of problems. Lots of folks get led astray on this, especially if they've used polyester resin (Bondo) products previously- with polyester, the 'Hardener' is a catalyst, and adding more catalyst makes the mixture 'hotter' and speeds up the cure.
With epoxy, the two components react together and you don't want any 'leftover' unreacted stuff at the end.

John

Hesh --

No shellac underneath, and I'm applying it to mahogany and granadillo. Haven't started in on the gran yet, though I'm guessing it'll be the same. Hopefully an extra day will help matters. Thanks for your input. I'd really like to figure this stuff out since, well, it's paid for.

John --

Thanks alot for your suggestions. I used to work with alot of polyester and urethane resins, and would intentionally over catalyze the mix -- the artist I was working for liked the way it cracked and fissured . And boy, did it ever get hot! Nasty stuff.

I may try to track down some syringes locally and try that route. Many thanks!

Ken

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Mountain Song Guitars www.mountainsongguitars.com

[QUOTE=skulpter]

I may try to track down some syringes locally and try that route. [/QUOTE]

Ken-
Once you convince your local surgical supply/drugstore folk that you're not using them for drugs, they're usually quite helpful in supplying you with syringes.
With the syringes, the printed markings do tend to smear if you get epoxy on them, so protecting them with clear tape sometimes helps.
Another 'trick' that works is to mark a measuring stick (for depth) with the 2:1 ratio (use pencil- some inks dissolve in epoxy) and mix in a straight-sided (cylindrical, not flaring) container. For small quantities a pill container or similar container can be used.


After having said all that, I just use the (WEST) epoxy pumps and throw away the excess (sometimes one shot is more than I need), though I usually have a jig or workboard that could use some epoxy coating, so I can use up the leftovers. Even with the pumps, you do have to check them from time to time with the 'stick and cylinder' method.

Epoxy is really useful stuff- now you can glue down those fingerboards without worrying about water warping the neck, etc.

Cheers
John