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Is this a sanding issue?
http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10102&t=15046		 Page 1 of 1
Author:  Ken Jones [ Tue Dec 18, 2007 4:09 pm ]
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Hello all --


I've completed two coats of straight pore filler plus one coat of 50/50 epoxy/da, and am generally pleased with my progress, except... I've got some dark spots on the end grain of one heel, as pictured below:



I was pretty darn meticulous with my sanding and prep, and the other heel looks quite good:



Any suggestions as to how to deal with this? I don't really know how I could sand it any more thoroughly than I already have. Is it possible that these dark areas are inherent in the wood grain? If this is the case, might I just have to live with it? Thanks for any input.


Ken
Author:  KenH [ Tue Dec 18, 2007 4:27 pm ]
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It is my experience that it is in the wood. No matter what you would have used for pore filling, this wood would have darkened in some places. The one place that I notice darkening more than others has always been on the heel of the neck. Another place is the tip end of the headstock where there is also end grain exposed.
Author:  Hesh [ Tue Dec 18, 2007 5:28 pm ]
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Yep that is the wood Ken.

But you can do this:  Prior to finish sanding, next time, hit that area with a damp rag, let dry, and sand - repeat this process several times.

It raises the grain in that area and let's you even it out somewhat with the sanding.  This is a trick that stainers use to even out the appearance of the stain on end grain.  It works too.  Even though we typically don't stain our necks this raising or the grain and then leveling will even out the natural color somewhat, not completely mind you, but it will be an improvement.

Also, this is a look that I like so perhaps just appreciate it for what it is?  Your necks look great to me!
Author:  Ken Jones [ Wed Dec 19, 2007 12:17 am ]
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Thanks for the input, Ken and Hesh. I was afraid that was the case, though I'm sure in the big picture it won't look so bad...I'l probably even grow to like it...


Surprisingly, I did raise the grain several times on each -- as I progressed through grits from 180 to 400. I guess that's just the beguiling nature of wood for ya. With mahogany in particular, I've noticed tremendous variations in color, weight, grain, etc. On thing if for sure -- it's one-piece neck/heels from now on.


Thanks again!


Ken
Author:  mgcain [ Wed Dec 19, 2007 12:31 am ]
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One question - did you seal the wood before you put on the pore filler?


You are dealing with short grain in that area of the neck.  Pore filling should always be done after first sealing the wood with at least a washcoat of [your sealer here] - I prefer shellac.  The pores and the short grain will soak up more of whatever you put on it, including pore filler. 

Author:  Hesh [ Wed Dec 19, 2007 12:51 am ]
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Mitch I would respectfully disagree with this statement about always sealing prior to pore filling when using an epoxy finishing resin.

The epoxy finishing resin is the seal coat.  Besides epoxy will not stick well to shellac although shellac sticks very well to epoxy.

A wash coat of epoxy and or a 50/50 epoxy denatured alcohol wash coat effectively does the same thing as a seal coat.

Some of the more traditional pore fillers such as the water based stuff that Stew-Mac sells and I struggled with for a couple of guitars with terrible results also recommend that no seal coat be applied first.  The seal coat can make the pores actually more difficult to seal since the filler will not stick as well.
Author:  Hesh [ Wed Dec 19, 2007 12:52 am ]
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And I should have added that this is one of the cool things about epoxy pore filler, no seal coat, fill and move on to finish.
Author:  mgcain [ Wed Dec 19, 2007 1:01 am ]
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Well, i will defer to your knowledge then Hesh as I have not ever used the epoxy pore fillers.  I have a pretty good background in finishing but admittedly more traditional.  Sealing before pore filling was always the cardinal rule.  So much to learn - I'll have to add 10 years to my life to get it all down...oh well!


I've never heard of anything that didn't stick to shellac though...that's a first!


 
Author:  Glen H [ Wed Dec 19, 2007 1:23 am ]
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The dark areas of the heel look to me like excess epoxy. It may be as the others have said, just in the wood, but if it were my heel, I would sand it back to bare wood again and see if it goes away. Then a thinned coat of epoxy to even it up.   
Author:  Ken Jones [ Wed Dec 19, 2007 7:00 am ]
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I'm tempted to agree with you Glen, though that's the only area on two necks and bodies that were affected. If anything, I tried to be more thorough with the heels because of the endgrain. I may try it anyway. It'd be well worth the effort if it works. If I did leave some epoxy behind, would it show up dark like that? I'm going to closely examine it and see if the dark areas cross over the glue line between the two pieces -- if so, it's definitely not in the wood. Thanks all!


Ken
Author:  Hesh [ Wed Dec 19, 2007 7:57 am ]
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Mitch my friend I am sure you have far more knowledge and experience with finishing wood then I do.  I may pick your brain at some point when I need help if you don't mind.

But a number of us have found out the hard way that epoxy does not want to stick to shellac.......  But shellac will stick very well to cured epoxy - go figure....  Michael Payne may be along to comment here, he has determined this too.
Author:  FishtownMike [ Wed Dec 19, 2007 8:14 am ]
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Ken was the standard pore filler tinted? Does anyone know if epoxy grain filler would work over a thinned coat of hide glue or thinned white glue? These can be used to seal the end grains prior to staining and grain filling with tinted fillers to prevent splotchyness. I have never used the epoxy sealers so I don't know.
Author:  Michael Dale Payne [ Wed Dec 19, 2007 8:47 am ]
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Well it is true shellac will stick well to very low friction surfaces (none porous surfaces with a low friction coefficient even polished glass) However epoxy needs to something with a higher friction coefficient than shellac provides to bond well.

I have tested shellac hardened and cured on clean plate glass then applied epoxy over it and allowed to cure at 75f for 30 days. You could peel the epoxy right off the shellac just like a candy wrapper leaving the shellac well bonded to the glass.

I tested the same but sanded a tooth into the shellac prior to applying the epoxy and it fared a bit better but still not create a bond I would trust.

I did each of these test 12 times with 4 different shellac batches and 4 different epoxy batches.

As simple as these tests were the failure rate was in the range of 7/12 for the sanded and 12/12 on the unsanded shellac.

I did these test because an epoxy vendor to my company had warned me of this issue. So I set out to prove or bunk the issue

I reversed the test a couple of times and the shellac would not peel of the epoxy without pulling epoxy with it. But this was pretty hard to pull get under the shella with out getting into the epoxy. but the other way was easy to get a hold of the epoxy and peel off the shellac. And most of the time with out taking any shellac with it.

I know a of some of builders do this but they all say they tooth the shellac first and that may be enough once a top coat is applied but I can't conceive of a good reason to risk an known issue.
Author:  Ken Jones [ Wed Dec 19, 2007 8:51 am ]
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Mike --


It's the System Three epoxy, no tint. Strange thing is, even in relatively thick section, it should remain clear. The thin coat is what's creating the gloss on there.
Author:  burbank [ Wed Dec 19, 2007 8:57 am ]
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[QUOTE=mgcain]

Well, i will defer to your knowledge then Hesh as I have not ever used the epoxy pore fillers. I have a pretty good background in finishing but admittedly more traditional. Sealing before pore filling was always the cardinal rule. <snip>
[/QUOTE

That's true if you're using traditional colored pore fillers, so that the color you want to fill in the pores with doesn't stain the wood too, creating a low-contrast, muddy look. But when using epoxy-based pore fillers, they have little or no color, so they're used as both sealer and pore filler.

Author:  Michael Dale Payne [ Wed Dec 19, 2007 8:59 am ]
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i would also like to say the adage to seal then fill comes from the days when spirit varnishes and French polishing were the most common finishes. then the some of the media used for the sealer would end up making part of the slurry used to fill. A good example of this is the spit coat of shellac prior to pumice filling.

Most every modern pore filler I have used warns against pore filling over existing finish or sealers.

But I have only used a few so that limits my expertise in fill medias out side of Pumice fill, egg white fill, water base fillers and Zpoxy.
Author:  Glen H [ Wed Dec 19, 2007 10:20 am ]
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Ken,
When I get the excess epoxy blotches, it's usually the same color as the wood (from dust) or a shade darker. I always get them on the neck one place or the other and end up having to tweak with sandpaper and thinned coats of epoxy (sometimes more than once). The discoloration I see in your picture looks identical to my excess epoxy residue with the exception of the color. I agree, it does looks a little too dark for the wood of your neck.
Good luck.
Author:  mgcain [ Wed Dec 19, 2007 11:19 am ]
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Michael et. al


This is good information - I will be having coffee on Saturday with an old buddy of mine who is a professional finisher and we'll kick this can around a little - Not that you guys aren't pros - ( How did this post suddenly feel like a Southwest Airlines commercial...wanna get away?)


His (and my) experiences are more architectural and probably explains how I've come to these conclusions...each system has its own way of doing things...It'll be good fodder for the discussions...


 
Author:  Michael Dale Payne [ Thu Dec 20, 2007 1:40 am ]
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No I use zpoxy and West System for the test. Why would you think the tint of the epoxy base would cause any more of a gloss than a clear base? The tint in Zpoxy is just the color of the epoxy base I assume to make it easy to idnify it from the hardener at a glance. It dries very transparent at about 50% of the color of the base. That is guess based on the fact that the hardener is clear.

I could be wrong here but every finishing resin epoxy I have ever used cured to basically the same surface smoothness if left unaltered and that includes system 3
i have nothing against system 3 by the way I just like the amber tint of Zpoxy.

Author:  Ken Jones [ Thu Dec 20, 2007 10:16 am ]
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Update:


I couldn't stand the thought of leaving things be, always wondering if more sanding would have mitigated the problem, so I went ahead and sanded it back down, thinking the whole time it wasn't doing any good, since I could still see the dark spots on the sanded down wood. However, with a thinned coat of epoxy applied, lo and behold:



Much improved! There's still some slight darkening near the top in the picture, but overall, it's much better. The other side looks way better as well. Thanks to all for your input!


Ken
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