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Hey all, long time since I posted on here. I’ve had a couple of guitars come back to me for repair with the same issue — in places where the hand is in contact with the finish, mainly the back of the neck, the lacquer has raised bumps with little hazy delaminations underneath. They appear as little white dots always directly over pores. Obviously it’s related to either heat or body chemistry , but I’d really like to know definitively what’s going on so as to avoid it going forward. My theory is that either the lacquer (Cardinal) is reacting to the player’s hand sweat/heat, then delaminating from the Zpoxy pore filler, or it’s taking the zpoxy with it and pulling it out of the pores. There’s also the fact that I use a barrier coat of shellac between them, so that could be at play as well. Here’s a look:


I know a lot of folks on here use that same combination, so I’m hoping someone has similar experience with this and can shed some light on what might be causing this recurring issue. Thanks in advance!


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Mountain Song Guitars www.mountainsongguitars.com

not sure if it is your issue but after zpoxy and other epoxies cure they leave an amine blush on the surface. This can cause even the seal coat to not adhere properly. Luckily enough the blush is water solvable and can be washed off.

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http://www.Harvestmoonguitars.com

Agree that it might be the result of amine blush. Also, verify that the shellac you’re using fully de-waxed.

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Andy
www.bounsallguitarworks.com

Would naphtha take off the amine blush? My final application of zpoxy I typically thin with grain alcohol and wipe it on, let cure, scuff sand to remove nibs, then pretty thoroughly wash it down with naphtha before applying shellac. My shellac is dewaxed platina flake.


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Mountain Song Guitars www.mountainsongguitars.com

Amine blush is a formation of 'salts'. Salts dissolve in water, they do not dissolve in thinners or spirits based products. Water works great to dissolve salts.

Zpoxy is on the bad side for amine blush.

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http://www.Harvestmoonguitars.com

I've used and like Z-poxy. I did have some spotty problems with blushing on one guitar. Sanding seemed to work on that one. Someone suggested a naphtha wipe and I didn't have the same problem on a couple subsequent guitars. Naphtha being a wetting agent might have helped removal w/o dissolving it. I'm not that good a chemist to say for sure.

From what I read after I think John has a point about solubility of some amines.

Even though it's about floor coatings, this article gave me plenty to think about with epoxy finish coatings or pore fill.

https://www.paintsquare.com/library/articles/Amine_Blushing_and_Blooming_of_Epoxy.pdf

I could understand the points made without the equations. Mostly have low humidity and a warm space to work in.

Made me think about recommendations to apply a solvent thinned epoxy for a final coat possibly causing condensation on the cooled surface under the right humidity conditions being a bad idea.

I think SilverTip is supposed to be designed to reduce amine problems if I remember right when I ordered some to try.

I also thought maybe an alcohol wipe post cure might be effective, but I'm just thinking and don't know for sure.

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Brian R, Wood Mechanic
N8ZED

I've used Z Poxy with good luck, but I've been moving back towards less "chemically" fillers like Aqua Coat or shellac and pumice. I've been using waterborne Enduro Var with Aqua Coat and I like what I'm getting. I still use a lot of shellac and french polish too.

I have autoimmune problems, and I've been moving more and more towards finishes that avoid weird chemicals as much as possible. I'd like to be able to keep doing this lutherie thing for awhile. But epoxy would be one of those weird chemicals...

Dave

I’ve used Z-Poxy on all of my guitars, and two with Cardinal.

The first Z/Cardinal guitar had some issues that made the finish look like a peeling sunburn. That turned out to be an adhesion problem. I can’t remember if it was because I didn’t use the Cardinal sealer at all, or if it was because I just waited too long after using it, but once I followed the sealer directions and sprayed the first coat of lacquer within 24 hours, all was well.


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Thanks for everyone’s feedback. I should mention that in both cases, it took several years for these issues to appear, and it’s primarily happening on the back of the neck. Also, I’ve used the Zpoxy/Cardinal combo successfully on at least 30 guitars, between builds and refins. That makes me think that in these two cases it likely has something to do with the owners’ body chemistry causing the lacquer to bubble, which then delaminates from the epoxy.


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Mountain Song Guitars www.mountainsongguitars.com

That was going to be my suggestion too if a result of longer term use.
Anything else tends to show up relatively soon after finishing.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

I have that sort of body chemistry and it does result in a rough feeling spotty back. I agree that it can be what you are seeing. I missed that this happened after a long period of time.

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http://www.Harvestmoonguitars.com

If the epoxy is not marketed as blush and bloom free, it is not. MAAS, System 3, and West all offer blush-free formulations, with System 3 Silvertip the preferred water-clear formulation used in the shop where I worked for a number of years. Z-Poxy - although easy to work with in terms of mixing and viscosity - is problematic with regard to blush, so was not in use in that shop.

Soap or detergent (as a wetting agent and surface tension modifier) and water is the usual treatment for epoxy-filled wood where the epoxy is blush-prone...use it prior to sanding back to wood or sanding to level. Even with this treatment, we refinished several Z-Poxy filled instruments with finish separations that showed up after 2-5 years. No issues with Silvertip or West 105/207 under lacquer, 2K polyurethane, or waterbased finishes such as Endurovar and High Performance since the transition to those fillers.

To be blunt, humans sweat and dump water, dead skin cells, filth, and salts onto guitar finishes. These penetrate lacquer and react with whatever is available. With a pH of less than 7, the reaction products between amine salts and perspiration may be visible beneath the surface. All of the guitars we refinished were owned by men (generally more acidic perspiration) and played on a daily basis.

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For the times they are a changin'

- Bob Dylan

Excellent info, Woodie, many thanks. I just ordered the quart size of the Sustem Three Silvertip. Honestly, I’ve been wanting to get away from Zpoxy for a while now, for other reasons, but now that I’ve been schooled on amine blush, I’m done. Too bad I just bought a new kit of Zpoxy...


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Mountain Song Guitars www.mountainsongguitars.com

I had something like that happen on a neck with water base KTM9, over zpoxy. It got gummy where the players hand was. I use to spray the water base directly on the zpoxy. About the time that happened, I switched to Cardinal Luthierlac over their vinyl sealer, over Clear Coat. My procedure since then has been System Three Clearcoat on bare, clean wood, dry for minimum 3 days in good conditions, (75-degree minimun for 72 hrs) up to 7 days if marginal conditions, (65-degree minimun for 72 hrs) followed by 2 coats Cardinal Vinyl sealer (10 minutes between coats, then within 20 minutes after sealer start 10 coats lutherlac.

No Problem Now!

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Joe Beaver
Maker of Sawdust

Ken, I had the same thing happen to me long ago. I no longer use epoxy out of caution.
Here's a link to my old post about it.
viewtopic.php?f=10101&t=33300

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Jim Watts
http://jameswattsguitars.com

Much like glues or finishes, there are products that work better for instrument fillers than others. Avoid blooming or blushing epoxies by sticking with products which are known to be suitable under guitar finishes like System3 Silvertip, West 105/207, or the MAAS blush and bloom-free formulations. Since going to Silvertip under lacquer, 2K poly, and EnduroVar, no issues in the shop where I worked, and as of last month, we had not seen any reports from other users of issues with those filler/finish combinations.

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For the times they are a changin'

- Bob Dylan