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Epoxy for more than pore filling? (pic)
http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10102&t=7102		 Page 1 of 1
Author:  Michael McBroom [ Mon Jun 12, 2006 9:58 am ]
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The guitar I'm working on right now has a very shallow dip in the back, next to the internal heel block. I'm way past removing the back to try and fix the problem from within, and I'm hoping there is a practical way to take care of this externally. It's largely cosmetic, but the little dip there is bothering me more and more, the more I look at it. I estimate the area to be about 2 square inches in area, and no more than 0.030" deep at its deepest part. Still, it's quite noticeable when light reflects off it, and it's held at the right angle.



The finish is french polish. I'm wondering if epoxy can be safely used. I have some 5-minute System 3, and some 30-minute Devcon. I've been planning on ordering some Z-poxy but haven't done so yet. I'm hoping that I can sand down the shellac slightly and feather epoxy into the finish.

What would you do?

Best,

Michael
Author:  Jim Watts [ Mon Jun 12, 2006 10:24 am ]
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Michael,
You can get optically clear epoxy (McMaster Carr)and I think if you degassed it in a vacuum youd have very good results. Although this would be a process development project.
I think degassing is probably the key and you'd need something with longer working time than 5 minutes to do this I think.
Author:  Robbie O'Brien [ Mon Jun 12, 2006 11:44 am ]
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epoxy works well as a leveling agent in areas such as rosettes, inlays etc. I have had good results with it. It does have a tendency to move around a bit under a finish while you are buffing if it gets too thick.
Author:  Brad Goodman [ Mon Jun 12, 2006 12:02 pm ]
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Michael,
If I was you I would forget about it and "go on with life".
Try to fix it on the next guitar-the only one who will ever notice it is you(and us).
I think it would get a lot worse before it got a lot better.
just my 2 cents
Author:  L. Presnall [ Mon Jun 12, 2006 12:13 pm ]
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Michael, is your shop dust-free? There's a speck so big on that guitar it looks like a DOG!! Really tho, I think if you layered up the z-poxy finishing resin making sure to keep it bubble-free, it may just do the trick...I've done some filling/fixing with it, but not over a 2in square area so it's just a guess!
Author:  Dennis Leahy [ Mon Jun 12, 2006 12:14 pm ]
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Hi Michael,

The Rakaepoxy I used at Grant Goltz's suggestion was exceptionally clear, much clearer than the Devcon I have used. They offer a sample kit for $18 that will fill this divot, as well as pore fill the next 4 or 5 guitars you do.

If you want Z-Poxy instead, check to see if you have a HobbyTown (franchise) in your area. They stock it.

Dennis
Author:  Michael McBroom [ Mon Jun 12, 2006 1:00 pm ]
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[QUOTE=L. Presnall] Michael, is your shop dust-free? There's a speck so big on that guitar it looks like a DOG!! [/QUOTE]

Hehe. Meet Rico. He's a ham. Just wouldn't stay out of the shot, no matter which way I turned.

Guys, if this were just my guitar, I wouldn't worry about it. But it's for a client. Classical players can get pretty fussy. Dunno if he's one of these or not, so I was thinking that if there would be a good way to fix the dip without the nightmare of making things worse, it would be worth a shot.

Best,

Michael
Author:  Jeff Doty [ Mon Jun 12, 2006 1:10 pm ]
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Michael,

Could you do anything like steam it from the inside a bit to loosen the area and then put pressure on it? Of course, attempting anything with a completed guitar is risky. Frank Ford where are you!   

It is so minor......the new owner would be a fool to complain.   

Jeff

Author:  Pwoolson [ Mon Jun 12, 2006 1:18 pm ]
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Yes, Michael. I'd be more conderned that the guitar is stuck to the back of your dog and he's trying with a vengence to knock it off with his paw.
I did quite a bit of this type of leveling on the first boat I built. Quite a bit because I was pretty green in the woodworking department. It worked well. Be careful not to sand down to bare wood around the divot when you are leveling it out or you will get a ring and there ain't no fixin' that unless you sand all of the epoxy off and start over.
I'd work in several thin coats and let them dry completely before applying the next. Also, a little boat building tip: apply epoxy in the hottest part of the day so the temp is falling as it is drying. that will prevent the gassing bubbles.
Author:  MSpencer [ Mon Jun 12, 2006 1:21 pm ]
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Michael,

Had a similar problem on the lower bout up from the tail block about 2-3" on a back. I was at a loss so I began to use some good old common sense thinking that the worse that could happen is I trash the guitar. It was minor but noticeable to me. Like Jeff stated above, I had not finished the guitar yet so I cut a series of little blocks with various lengths to where I could wedge from a top brace up to the affected area. The first block was tight, the second I cut a little longer and it was tighter, and so on and so on until I felt I had the block that would put the back to where I wanted it to level the top better. I used steam as well, my wifes thing she hangs cloths on and steams to get the wrinkles out, it has a directional wand. I started out slow and heated the wood using the steam with the first block, slowly progressed up until I had the last one in as the wood had more moisture and heat. After in I had to cut another small one to do a little last minute leveling. I left it like this for a couple of days and started working on another guitar. After it had dried and sat for a while I popped the block out and the wave was gone or now unoticeable to me. It has continued to hold and has only been a few months but no signs of it returning.

Yours is more severe and covers a larger area, nobody really told me to do this but it worked for me.

Mike
White Oak, Texas
Author:  Dennis Leahy [ Mon Jun 12, 2006 1:29 pm ]
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[QUOTE=Pwoolson] Also, a little boat building tip: apply epoxy in the hottest part of the day so the temp is falling as it is drying. that will prevent the gassing bubbles. [/QUOTE] I got the same advice from Grant Goltz, who makes some of the most beautiful wood/epoxy resin canoes and kayaks I have ever seen. He says you can also pre-heat the area with a hairdryer (obviously in this case, not too much.)

Dennis
Author:  rlabbe [ Tue Jun 13, 2006 2:20 am ]
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I don't think you are going to be happy with the epoxy.

First, epoxy doesn't stick to shellac, so you'll need to go back to raw wood. Oh, it'll probably stick all right while you do the repair, but down the road? Peel city.

Second, it is optically clear, so you will still see the dip. Try it on scrap. Ding a piece of pine with a hammer or something, level it with epoxy, and french polish the result. You'll still see the dip. If anything, it's more apparent.

Author:  Michael Dale Payne [ Tue Jun 13, 2006 2:41 am ]
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I have done this in some very small areas. Depending on the type of wood and if the dip is cause by over aggressive sanding in that area or a warp in the joined planks would determine the course of action

If the back is warped (relative even thickness) then I might be more likely to try to steam the perimeters of the dip a bit and add internal jacks to support the dip till the wood dries out. this will require that you remove finish down to the wood in the affected area and it surrounding area.

If you over aggressively sand in that area then a fill may be your only resolution
MichaelP38881.4887152778
Author:  John How [ Tue Jun 13, 2006 2:42 am ]
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I have to agree with Brad, If you fill it you will still see it and it will look just like it was filled. I would either leave it as is or re-attach the back.
Do you use a radius dish when you glue your plates on? I had this on one guitar and since then I have either used a dish for a clamping cawl or I make very sure that my clamps are only applying presure over the side and not onto the back inside the sides, and always have the sides in the mold to keep everything in place.
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