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The back of my recent Waterfall Bubinga still has too many visible pores. Prior to beginning the FP sessions, I carded on Zpoxy and sanded back several times to achieve a smooth, pore filled surface. As a final application, I cut the epoxy in half with denatured alcohol and wiped it on.

Prior to beginning the sessions, I sanded back down to bare wood with 400 grit, just leaving the pores filled...at least I thought they were filled!?

As far as my experience with Zpoxy for pore filling...I've filled in preparation for several woods and finishes. After I completed the first few FP sessions, it almost looked like the alcohol was dissolving out the epoxy in the filled pores.

Am I crazy, or can this happen to cured epoxy. (The first option is certainly a distinct possibility) Nonetheless, I'll be sanding down to bare wood and trying to fill in the pores with pumice.

I'm hoping that Robbie and Michael can shed some light on this.

TIA

BTW...this didn't happen on the sides...they look very smooth and pore free.

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JJ
Napa, CA
http://www.DonohueGuitars.com

JJ: From a purely chemical standpoint, I cannot imagine that alchohol can dissolve properly cured epoxy. But my experience with FP is zero.

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"Building guitars looks hard, but it's actually much harder than it looks." Tom Buck

JJ, from my experience, I think I know what you might have done. I'm guessing the first coat of epoxy sort of bridged the pores rather than sinking down into them. When you sanded, you opened up the bridge. That's happened to me on wood with small, yet deep and abundent pores.
I really doubt that the alcohol melted the cured epoxy.

I'm gonna guess that the epoxy was over the pores instead of in them. When you sanded back to wood, the epoxy dust filled the pores, then the alcohol washed the dust from the pores. Just a theory, I may be totally wrong, but it may be the answer. Try some thickened epoxy on some scap,and rub it in to force it into the pores.

Al

JJ are you saying that the pores are re-apearing? If not then I am not following what you mean by "dissolving the epoxy out of the pores."

I have never had any issues like this and the alcohol will not dissolve the epoxy providing it is 100% cured.

By the way the Zpoxy carton states that it hardens to the touch in 3 hours. This is not full cure. It takes 24 hours to fully cure if at 68F or higher room temp.

If what you are seeing is that the pores are a higher sheen than the rest of your wood after three body sessions then I think you just noticing the lubricant oil your using rising to the surface in spots.

If you are seeing pore depressions then you did not get the pores filled. Zpoxy is not real bad about mix ratio, but it does need to be with in 5%. Also after about 10-15min the zpoxy starts to thicken and is more likely to bridge the pores than to fill them. and the after sand back cut wash coat needs to cure 24 hours as well.

Michael...It's definitely not oil rising to the surface...I did lots of stiffing and glazing. I actually used oil sparingly during the process, using just a tiny drop only when needed. It's definitely unfilled pores.

Paul...I think the explanation you gave related to the bridging and breaking while sanding sounds like it might be the problem. These pores are many and very small. Just as a comparison, I zpoxy filled walnut and the pores remained filled. Pores on this wood seem much smaller and more numerous.

In the case of this particular wood, I'm thinking that pumice might have been a better choice.

So...going forward, if I want to correct this, it seems like I have the following options:

1) Partially sand back with something like 320 or 400 grit and re-apply Zpoxy
2) Partially sand back and pumice the surface to get the pores leveled.
3) Totally sand back, add a few spitt coats of shellac and begin the pumicing process to fill pores.

It's not like the surface is terrible...in fact it's quite apppealing. I just think I can get it better. As long as I feel this way it'll drive me nuts. Are there other options? Which makes most sense?

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JJ
Napa, CA
http://www.DonohueGuitars.com

If you are going to take off the shellac completely I would do one more fill with Zpoxy. mix small batches as you need them, use in 10 min or less. allow to cure 24 hours.

If you do deside to pumice fill I am assuming that you have done this before. As you may know it is a much more tempermental fill process than epoxy.

I've never used pumice. I realize the reputation it has but figure I can work it through if that's the path I take. I have some scrap that I can practice on before I decide. In any case, I figure if I'm going to do further guitars with FP, I need to develop a pumicing technique sooner or later. Any tips beyond what the Milburns recommend would be appreciated.

Sounds like the Zpoxy is easier ... I'll just have to work it in better until I'm sure that everything is properly leveled.

I'm going to stew on this for a while. It's unfortunate that I don't have an expert close by that I could show the issue to in person. Figuring this subjective stuff out via the forum is frustrating...but I really do appreciate all the advice...thanks.

The key lesson I've learned regarding FP is that surface prep and gap filling are MUCH more critical than for the other finishes I've tried. The thin coat of shellac has Zero tolerance for surface imperfections. Taking extra time up front is a must. The Milburns stress this but I may have underestimated its importance.

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JJ
Napa, CA
http://www.DonohueGuitars.com

JJ, the thought occurs to me--and I'm no expert at this by any means--that a Zpoxy fill on the sides, and a pumice fill on the back might end up looking slightly different. Slight, granted, as you said that the pores are small. Perhaps if you are experimenting, you could try a zpoxy fill side by side w/ a pumice fill, and see if there is any visible difference.

Steve

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From Nacogdoches...the oldest town in Texas.

http://www.stephenkinnaird.com

Excellent point, Steve! I think you may have just caused me to take the Zpoxy path. Thanks for watching my back!

I can always practice pumicing before the next effort.

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JJ
Napa, CA
http://www.DonohueGuitars.com

jj, I think it's very do-able with zpoxy. You might consider thinning it from the get-go and doing several thin coats. That way you're more sure to get them filled rather than bridged. Hope it works out for you.
Weren't you coming this way sometime? I don't remember when that was. If it is still to be, bring the guitar and maybe we can put our heads together on it.

[QUOTE=JJ Donohue] Thanks for watching my back!

[/QUOTE]

Certainly! Afterall, you're going to have to build mine, remember???

SK

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From Nacogdoches...the oldest town in Texas.

http://www.stephenkinnaird.com

JJ when you practice pumice filling be sure and not get your spit coats on too thick and clear as in transparent all pumice on the muneca before touching the body with the pumice. Keep in mind that wood fiber is what makes up well over half of the slurry that fills the pores the rest is shellac and residual pumice. If the spit coats are on too thick to allow the pumice to abrase fibers off of the body then all that will happen is a gummy mess as the shellac and pumice cake up together. little or no added shellac and conservative on the alcohol when filling. If you use too much alcohol during the pumice fill the residual shellac in the inner pad will flow too strong and you will gum up. Less is better than more here in most all components.MichaelP38965.582650463

Paul...I was in MadTown early last week with Frank but was totally focused on the school thing for an entire day. BTW, the campus is just too cool! I'll be up that way within a month and be sure to stop by. Thanks for the offer...I'll give you a week or so notice. I like the thin Zpoxy approach but will wait till after our meeting.

Steve...You're on your own my friend! I would never assume that I could even sharpen a chisel for you. I'm just hopeful that you get that zoot out of the closet and show me what I need to shoot for with my second set.

BTW...the bending was relatively problem free...it's just the sanding that took a lot of effort to get it leveled out. Since the grain is traveling in so many different directions, it has all those humps and bumps that require a lot of post-bending attention.

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JJ
Napa, CA
http://www.DonohueGuitars.com

JJ,

I have no experience here but I remember seeing a photo on David Hurd's site regarding filling with epoxy. David used either a hair dryer of a heat gun to help the epoxy flow and fill the pores. He also scraped with an old credit card to help the pores and to remove excess. Hope it helps.

Good Luck

Philip

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aka konacat

If you think my playing is bad you should hear me sing!
Practice breeds confidence and confidence breeds competence. Unfortunately, I'm stuck in practice.

Here's a thought. After I filled with epoxy and buffed out the KTM-9 finish on mine, it sat in the shop for about two months at a controlled 45% humidity. I was very pleased at the mirror finish and no shrinkage into pores.

But, within a couple of days after bringing it upstairs into the house at the 80% New England humidity in July, the pores were showing. That was an eye-opener, and in my opinion that cannot possibly be a matter of epoxy or the finish curing more and shrinking back into the pores. It's obviously a matter of the wood swelling up around the pores after being subjected to the much higher humidity. I haven't done this, but I'm betting if I let the instrument re-equillibrate in the shop, the pores would again diminish. Of course I don't plan on doing that ... I'll just wait for winter instead!   

With regard to your problem, I'm wondering if the alcohol (and small percentage of H20 in the alcohol) isn't migrating into the wood and swelling it around the pores, giving the appearance of sunken pores or that the alcohol was slightly "dissolving the epoxy". I can't even venture a guess if this would be possible, but based on my experience above, I thought I would mention it.

If there's not a lot of pores, you can just use pumice to fill them now. Yes, it's a bit harder once you have shellac built up, but there is no reason why you can't do it. I've done this a few times when I missed a few pores with the epoxy fill.

[QUOTE=MichaelP]

If you do deside to pumice fill I am assuming that you have done this before. As you may know it is a much more tempermental fill process than epoxy.[/QUOTE]

Tell me about it!!!!