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Another one about zpoxy - dark spots
http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10102&t=15062		 Page 1 of 1
Author:  Lars Rasmussen [ Thu Dec 20, 2007 3:29 am ]
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Hi all, I just did pore filling on these two guitars, and have some problems with dark areas.

The process have been:
one thick coat to start with, then sanding back to wood except where there was uneven levels in the wood, leaving areas (islands) of epoxy. Then another coat to fill the last few pores.

I then put a washcoat of zpoxy-alcohol(70-30) to even out the color, something ive read on this forum its possible to do. But the 'islands' of zpoxy are still very evidently darker in color. Is this something I will have to live with?



Less evident on the ziricote guitar, but you still see some.



Have I understood the trick wrong? I have used zpoxy on two prior instruments, both very dark brw, so this problem havnt been visible before.

Well, just I thought Id throw out the question.
Author:  Hesh [ Thu Dec 20, 2007 3:40 am ]
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Lars my friend there are two schools of thought on using epoxy finishing resins to pore fill:  One is to sand back to the wood leaving it only in the pores.  The other is to leave a very thin film on the entire surface of the wood. 

For people who leave a thin film on, like me, the wash coat of 50/50 is applied to help even out the color where we may have sanded through but the wash coat is evenly applied to the entire areas that we pored filled.

From your very good description of your methodology it sounds like you used parts of both methods, sanding back leaving it only in the pores in some places and leaving "islands" of epoxy film in other areas.  Hence, IMHO the darker spots.

What I would do is either method but if sanding back to leave it only in the pore do exactly that, no islands and no wash coat.

If I was leaving a thin film I would likewise endeavor to have the film on the entire guitar (not the top) and then use the 50/50 wash coat.

The root cause and why you left some islands here may be that the wood is not very level in these spots.  Perhaps more level sanding prior to pore filling is advisable?
Author:  Michael Dale Payne [ Thu Dec 20, 2007 4:06 am ]
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Lars,

I do not like to see the initial pore fill leave much film thickness at all. One every filling session I scrap off all excess epoxy as much as humanly possible. i want epoxy only in the pores. Now that is really impossible as the surface tension of the epoxy will cause you to leave at least a very minor film on the wood.

If you build a heavy film then level out you are likely to not truly level parallel to the woods surface. this means as you sand back the film will smooth out with some areas deeper than others which will mean you will reach wood in some areas and still have a dense film in others and end up with what has happened.

Also a 70/30 cut of epoxy is so thin that it is not likely to equal the the thickness of the islands you left. 60/40 or 50/50 would have been better

Now for the good news. I am assuming that you have not seal coated the guitars as of yet. This disparity may very well disappear or at least be toned down with a couple seal coats of 2# shellac Or you could even make up a 50/50 cut of epoxy "first"(as in prior to any shellac!!!!!!!!!) and make an other rag on application. avoiding build up at the islands and then lightly level again.
Author:  WaddyThomson [ Thu Dec 20, 2007 4:14 am ]
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I have not done this, yet, but I think Hesh is right.  It sounds, from your description, and I could be mis-reading it, but using the epoxy to level uneven places in the surface is probably not a good idea.  It should either be level before starting, or sand back to wood everywhere, then use the 60/40 or 50/50 mix coat all over the surface to even out the color in areas where a minute film of epoxy might be left.  If there is an uneven surface when you start, then it should still be uneven when finished.  Otherwise, sand it back until the uneven surfaces are gone, then re-fill those, then do the wash coat.  Just my perception of the issue.  Wait till someone else weighs in to take action.
Author:  WaddyThomson [ Thu Dec 20, 2007 4:15 am ]
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I bow to Michael's post.  
Author:  Philip Perdue [ Thu Dec 20, 2007 5:08 am ]
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I have a few questions about Zpoxy myself as I am about to use it for the first time. The guitar is Bubinga with ebony bindings. It doesn’t look like there are pores to fill like with mahogany so here is my plan. First, I was going to apply Zpoxy and squeegee it thin. Second, would be a 50/50 wash coat. How is this applied? Third is to finish with Tru-oil.

Although different, I have a mahogany soprano ukulele I completed to practice on.

Thank You

Philip
Author:  Michael Dale Payne [ Thu Dec 20, 2007 6:32 am ]
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If referring to 50/50 wash coat use a lint free cloth and apply in slightly overlapping with the grain strokes much like glazing and spiriting off in a French polish session.

Be sure to allow 24 hours to cure before doing any leveling on either process.

The 60/40 or 50/50 mix will flash very quickly so make in small batches that can be applied in a few minutes. If you try to make too big of a batch the alcohol will flash out to quickly leaving a too thick of mix to use as a wash coat.
Author:  Lars Rasmussen [ Thu Dec 20, 2007 8:00 am ]
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Thanks for your input everybody. Seems like its sanding back to wood thats the cure for my problem... Well, I have only used the zpoxy on very dark woods(brw) earlier so this havnt been such an evident problem yet, but now it all makes sense to me. The cut I used for wash coat was 70 epoxy/30 alceehol, sorry if i was unclear on that point.

Ok, Ill sand back, and do a 50/50 wash coat. Man this forum is great!

How to you guys do on the rims? I always end up with ripples and dips all over the place. Do you grind the rim extremely thin before filling or do you fill with laquer? Or do I have a method of bending that needs inprovement?
Author:  Hesh [ Thu Dec 20, 2007 8:12 am ]
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Lars I use a Fox style bender and get very smooth rims to start.

But I always use a block, wider then the rim, and 120 paper and sand the rims even and true all the way across and around.  In the waste area I have a 2" wide dowel that is longer then the width of the guitar that I stick sand paper on and true up that area.

I am not sure if you are asking about the rims in terms of surface preparation or Z-Poxy (epoxy) application.

For applying epoxy I use Steve's credit card... moving and mashing 45 degrees to the grain and in all other directions too.  The real trick for using a credit card or a squeegee for that matter is to mash the epoxy into the pores NOT to just remove excess.....  After I have really mashed the epoxy down from all directions then I use the squeegee action of Steve's credit card or the squeegee to remove as much as I can from the surface but only moving at 45 degrees to the grain direction.  For the bindings I wipe off and in the build-up with an alcohol dampened lint free rag.
Author:  Michael Dale Payne [ Thu Dec 20, 2007 8:37 am ]
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Ripples in your bent sides is a sign of excess moisture left in your sides after bending causing cupping and warping.

Cut down on the water used during bending so that it all cooks off. if using a fox style bender do more than one cook after bending. leave clamped in place in the bender over night.

All imperfection, which should not be much at all, need to be sanded out prior to your pore filling. Actually do this prior to binding so that you end up with consistent binding thickness after all the prep sanding is done. If you don't handle those waves in the bent side before you cut your binding channel then the bearing on your bit will follow those waves and you will have inconsistent binding channel depth leading to varying binding thickness after prep sanding.

As far as getting the zpoxy on the sides with out dripping; I use a smaller piece of credit card and load the zpoxy on to the card not the side. I work one side from mortise to end graft working is small areas at a time and allow to cure before moving to the other side. If you are dripping zpoxy you are using way too much per load up. A little more than tear drop size will go along way about 1/8 or more of a side for one session. In fact half a teaspoon will cover both sides for one session.

Having read this question from you. Can you tell me how many ounces of epoxy you used per session on the back by its self. If the answer to that question is more than a half an ounce then you are using way too much. Remember it is not about building a film on the guitar it is only about getting it into the pores level with the surface. I suspect this is where you problems originate.

I am not sure you are doing your prep sanding prior to pore filling. You really should or you end up filling inperfection of the wood with epoxy wich in part could be related to the issue you have.
Author:  Michael Dale Payne [ Thu Dec 20, 2007 8:57 am ]
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This brings up a point that may be of some help to you.

Just like with shellac when pumice filling, if you just apply a film to the surface without working the epoxy into the pores. The surface tension of the epoxy will allow it to bridge the pores, at least some of them and appear to be filled but in fact there is a void below the surface tension formed film. As a result when the epoxy cures and is sanded back to just the wood surface you will have unfilled pores. If you don't sand back then the epoxy will eventually shrink back and you will have dreaded pore shrink back.

This is why I suggest you work in small areas at a time leaving no more film thickness than you can. squeegeeing the epoxy into the pores,not spreading it over the wood surface. You cant help building a very thin film but you can keep it from amounting to more than ulta fine tissue thickness.
Author:  MaxBishop [ Thu Dec 20, 2007 11:50 pm ]
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Hesh,

You wrote,"For the bindings I wipe off and in the build-up with an alcohol dampened lint free rag."

What you are saying here escapes me. Could you reword this a bit?

Thanks,
Max
Author:  Hesh [ Fri Dec 21, 2007 12:06 am ]
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Sure Max - since you can't use a squeegee or credit card well on a cornered surface like the binding I use a lint free rag dampened in denatured alcohol to smooth out and press into the pores the epoxy build up.  Epoxy tends to build up in these areas because you can't get at them will with cards and squeegees.

What I have been trying to get across in this thread is that the credit type card or squeegee is not just to remove excess epoxy.  You have to use these things to "press" the epoxy into the pores from all directions first and finish up with the removal of excess epoxy and the squeegee action of the cards or squeegees.

The same holds true when using a rag or your finger in a latex glove.  Press the epoxy into the pores first, butter it on and in and then skim the excess off the top. 
Author:  Arnt Rian [ Fri Dec 21, 2007 1:53 am ]
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Hei Lars!

When I use z-poxy I sand back to bare wood, and in doing so I have noticed that areas of the back between the braces will deflect a bit. Just when I get down to bare wood over the braces, there will be epoxy left on these 'deflecting' areas that look somewhat like your darker areas. I don't think this is what is happening in your case though; the blotchy areas on the lighter back look like they are independent of the braces. On the ziricote back (great looking zoot, by the way!) it looks a bit like ladder braces are telegraphing through...?
Author:  Philip Perdue [ Fri Dec 21, 2007 6:34 am ]
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I just remembered something I saw on David Hurd's web site. When he is working with epoxy for pore filling he uses a hair dryer on high to lower the viscosity of the resin for better pore pentration. This sounds like a good idea for an open pore situation. I think I will try it out on the mahogany ukulele I'm about to pore fill. It will be my first atempt with zpoxy and it will be a good preview of the properties before I use it on my guitar.

Philip
Author:  John K [ Fri Dec 21, 2007 11:11 am ]
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I think what you are noticing in the dark spots is a collection of pigments from the wood that dissolve into the epoxie before it hardens. If you start off with a thin wash coat to seal the wood and seal in those pigments so that they do not color the epoxie pool, then on the second application of epoxie you can do some leveling with thicker areas and avoid the freckles.

You might also consider using a scraper for leveling sides. It bridges the low spots, hits the highs and makes a very crisp looking finish. If you sharpen your scraper well you do not have to sand after scraping.
Author:  Terry Stowell [ Sat Dec 22, 2007 12:39 am ]
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This is not helpful to you, but I LOVE that Ziricote. Is there a sister set to that? Been looking for that for a few years now.
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