Page 1 of 2 12 LastLast
Results 1 to 25 of 27

Thread: how to remove epoxy on the top sound board ?

  1. #1

    Default how to remove epoxy on the top sound board ?

    I have repaired a broken violin (falling on concrete ground) using proper methods and HHG. Now I am asked to repair a broken cello, similar damage (one long crack on the top board and a few cracks on the side).
    The owner has fixed the long crack using epoxy which now shows as a yellowish stuff. He did not flatten the epoxy on the top while it is still liquid. Now the top sound board has an ugly mess along the crack.
    My goal is to use HHG to close up the crack, then add cleats on the inside to keep the crack closed for good. I have not remove the top sound board yet (in order to repair the cracks on the sides).
    I am asking for advise as to how to remove this epoxy thing without creating addition damage to the top.
    Thanks in advance for any advise given to me.

  2. #2
    Teacher, luthier
    Join Date
    Oct 2017
    Location
    Southeast Tennessee
    Posts
    718

    Default Re: how to remove epoxy on the top sound board ?

    You can mask the outer edges of the cutting surface of a scraper with blue masking tape, leaving only the middle of the blade exposed. The masked surfaces ride along the top while the center of the scraper cuts. Use several layers of tape to start, then peel them off one by one as the work progresses. When you are nearly level, you can switch to a double layer of Scotch magic tape or the equivalent. Check the tape often to make sure it is not wearing out. I would also mask of the top during the preliminary stages of the epoxy removal. If a flat scraper won't work because of the top curvature, you can make a radiused sanding block and mask off most of the sandpaper, again leaving a cutting surface only in the middle of the block. Again, check the tape frequently to make sure it is not wearing through.

    With patience and a little luck, you can get the epoxy off with minimal damage to the finish. Unless you're very good AND very lucky, you'll still have to do some minor touchup work. You're also going to have to find a way to get the epoxy out of the crack. Hide glue won't stick to it.

  3. #3

    Default Re: how to remove epoxy on the top sound board ?

    You're also going to have to find a way to get the epoxy out of the crack
    That's the part I am wondering about. Will a hot thin blade melt it out ?

  4. #4

    Default Re: how to remove epoxy on the top sound board ?

    Here are some photos showing the damages, one on top and one for each side of the cello.

    top damaged (reglued !!!)
    Click image for larger version. 

Name:	20180220_164048.jpg 
Views:	92 
Size:	335.0 KB 
ID:	165212

    side damanges:
    Click image for larger version. 

Name:	20180220_164136.jpg 
Views:	56 
Size:	196.1 KB 
ID:	165213

    Click image for larger version. 

Name:	20180220_164224.jpg 
Views:	61 
Size:	170.4 KB 
ID:	165214

    Hope that with the top photo, I can get more opinions.
    After knowing how to deal with the top, I will remove the top board and fix the cracks on the side like I did with the damaged violin.

  5. #5
    Registered User
    Join Date
    Jan 2009
    Location
    S.W. Wisconsin
    Posts
    4,469

    Default Re: how to remove epoxy on the top sound board ?

    Looking at this I am not sure I would try to remove the epoxy from the crack. Level it out and cover it the best you can. It will hold the crack together, but the only way to glue this with HHG would be cut out the top for a spline and glue the spline in. The epoxy will have sucked into the wood and the HHG won't be able to do the same so it won't hold very well no matter how you try to clean the epoxy. I am not a fan of cleats, and have done lots of serious cracks over decades without cleats. Full strength HHG will be strong and the center seam is glued without cleats, and doesn't seem to have a problem if it is done right.
    THE WORLD IS A BETTER PLACE JUST FOR YOUR SMILE!

  6. #6
    Teacher, luthier
    Join Date
    Oct 2017
    Location
    Southeast Tennessee
    Posts
    718

    Default Re: how to remove epoxy on the top sound board ?

    In the world of violin repair, it is not unusual to loosen the top or back plate to make it possible to close an open crack and clamp it securely. This is a luxury that is not available in the fretted instrument world. I would clean the glue from the outside of the crack, loosen the top seam, and carefully regularize the crack with sandpaper pulls. That's the short version. With care and a little bit of luck, you might be able to get away with not splinting the crack.

    I repaired a long side crack that had been epoxied out of line a while back. I used the masked scraper to get rid of the outside glue. Some of the glue inside the crack just fell right out of there. I cleaned the rest of it out with sandpaper pulls. Some of the old glue was very brittle and I may have chipped some of it out with something-- I don't remember exactly how. The crack was so long that there was enough flex in to close the crack with clamps. I used hot hide glue. I may have used a tiny bit of filler in a couple of spots, but I don't remember for sure. If I did, it would have been glue and rosewood dust. The finish repair was done with shellac, pumice, several coats of oil varnish, and several French polished top coats. Because the repair was in fairly dark piece of rosewood, and because of the French polish technique known as "loading" with shellac and pumice, the crack is pretty much invisible. A lot of slow work, though.

    I don't think you can get an invisible repair on the 'cello with the light woods and finish, but with patience, you could get a reasonably clean repair. It wouldn't hurt to use a few cleats on the side cracks. On the top crack, that depends on how good a fit you can get. Most high class violin repairmen like to use a few paper thin cleats on crack repairs.

  7. #7
    Registered User
    Join Date
    Jan 2009
    Location
    S.W. Wisconsin
    Posts
    4,469

    Default Re: how to remove epoxy on the top sound board ?

    Actually in looking a second time that looks more like gorilla glue than epoxy. I have had to deal with that a few times, it is not pleasant. As rcc56 says loosening the top and closing the crack is what I would do also for violin family instruments. The glue is a major pain and the way it looks foamy doesn't look like epoxy. Are you sure that's what was used?
    THE WORLD IS A BETTER PLACE JUST FOR YOUR SMILE!

  8. #8
    Registered User
    Join Date
    Feb 2011
    Location
    Conneaut Lake, PA
    Posts
    3,831

    Default Re: how to remove epoxy on the top sound board ?

    That is Gorilla glue for sure. There is really no way to remove it except scraping it out. Good luck.
    Don

    Weber Custom Bitterroot F
    Weber Bitterroot A
    Fender Octave Mandolin

  9. #9
    Registered User Greg Mirken's Avatar
    Join Date
    May 2008
    Location
    Nevada City, CA
    Posts
    215

    Default Re: how to remove epoxy on the top sound board ?

    The owner has done a fine job of transforming that from an instrument to a decorator item or planter. There's no sensible way to undo that mess.
    Shade Tree Fretted Instrument Repair
    Now located in Nevada City, California
    http://www.shadetreeguitars.com

  10. The following members say thank you to Greg Mirken for this post:


  11. #10
    Teacher, luthier
    Join Date
    Oct 2017
    Location
    Southeast Tennessee
    Posts
    718

    Default Re: how to remove epoxy on the top sound board ?

    Oh, it's repairable. It will take a lot of work to do a nice job. The repairs will be visible, how visible depends on your touchup skills.

    Is it worth it? Yes, if it's a good instrument, or if you're wanting to hone your skills. But if you charge by the hour, the owner will probably be very upset.

  12. The following members say thank you to rcc56 for this post:


  13. #11

    Default Re: how to remove epoxy on the top sound board ?

    Thanks for all the valuable advise. I never used Gorilla glue before so can't recognize it.
    Anyway, I had lots luck yesterday removing it. Here is what I did:
    1) put two thin blades (thin feeler gauge) on both side of the excess glue
    2) use a hot blade, gliding on these two thin blades, to cut thru the excess. The excess glue is cut off easily like tofu
    3) the remaining thin layer of glue becomes very soft and I peeled it off with just finger nails

    Here is the photo showing the crack after this work
    Click image for larger version. 

Name:	cello04.jpg 
Views:	89 
Size:	325.5 KB 
ID:	165239

    Now, it looks much better.

    Next step: I open lose the top plate on the side of the crack and follow the advise below (many thanks) to clean off the Gorilla glue

    carefully regularize the crack with sandpaper pulls
    Note: I will have to remove the top sound board to fix up the cracks on the sides anyway. This is the easy part as there is no wood loss. I have never been good at finishing / touching up finish on instruments. Any touch up I did turn DARK !!!
    Really love to learn hand on from someone.

    I will post my progress so others can offer me more advises as I go. This is how I learn repairing instruments, thanks to experts in this forum.

  14. #12

    Default Re: how to remove epoxy on the top sound board ?

    This is a Cremona SC-200 cello, costing around 900$ brand new. Yesterday, the owner (father of the girl who plays) SOLD it to me for 65$ , cheap due to that ugly excess glue. So I took the chance to buy this cello as I have repaired a violin with similar damages (3 months ago).
    I bought one (about 18 months ago) another cello with a broken neck for 50$. I successfully repaired it, played it for 6 months to ensure it's good and sold it as it is too small for me (1/2 size).
    It's kind of fun for me to hunt for broken instruments for cheap and learn to repair them.

  15. The following members say thank you to kkmm for this post:

    fox 

  16. #13
    Registered User Greg Mirken's Avatar
    Join Date
    May 2008
    Location
    Nevada City, CA
    Posts
    215

    Default Re: how to remove epoxy on the top sound board ?

    I didn't say it wasn't repairable. The photos show that this is a modest instrument. If someone brought this in to my shop I'd have to tell them the cost of the repair would exceed the value of the thing.
    But for a sixty-five dollar investment and a desire to learn more about instrument repair, that's a whole different story.
    Shade Tree Fretted Instrument Repair
    Now located in Nevada City, California
    http://www.shadetreeguitars.com

  17. #14

    Default Re: how to remove epoxy on the top sound board ?

    Yes, it is a student instrument. The owner appears to be aware of the repair cost and just dumps it cheap.
    He bought a new one for his daughter. By curiosity, how much is the typical repair cost based on the original photos I posted.

    I will fill the crack with HHG and clamp it for 24 hours. The crack near the F hole appears to be wider and may not close tight when clamping (the old glue has been craped off with a thin razor blade and sand paper). I will fill the little gap with wood shaving (and HHG), this is something I just learned from another active thread (about whether the cracks on top sound board should be repaired or not).

  18. #15

    Default Re: how to remove epoxy on the top sound board ?

    Update after a few days working fixing the cracks.

    top crack after repair and finish touch up (the best I could do)
    Click image for larger version. 

Name:	sm7.jpg 
Views:	80 
Size:	88.8 KB 
ID:	165354

    Crack on one side of the rib
    Click image for larger version. 

Name:	sm5.jpg 
Views:	60 
Size:	164.6 KB 
ID:	165355

    Crack on other side of the rib
    Click image for larger version. 

Name:	sm6.jpg 
Views:	57 
Size:	130.3 KB 
ID:	165356

    Cleats were used to ensure the cracks will not open in the future.

    The top is now ready to be glued back to the body using weak HHG.
    But I have to get (or make) some spool clamps first.

  19. #16
    Registered User
    Join Date
    Jan 2009
    Location
    S.W. Wisconsin
    Posts
    4,469

    Default Re: how to remove epoxy on the top sound board ?

    You can use cam clamps if you have them. Do a section at a time, glue and clamp. glue and clamp. If you only have a few it will take longer, but the end result will be the same.
    Looks like it will be a playable instrument when you are done, good job.
    THE WORLD IS A BETTER PLACE JUST FOR YOUR SMILE!

  20. #17

    Default Re: how to remove epoxy on the top sound board ?

    I forgot about matching the top with the ribs. A quick look shows I will have to do some work to ensure there is no gap between the top and the ribs. I do not want to clamp hard to close these gap.
    And yes, my goal is to make it a playable instrument. I do play cello a little bit.

  21. #18
    Registered User
    Join Date
    Jan 2009
    Location
    S.W. Wisconsin
    Posts
    4,469

    Default Re: how to remove epoxy on the top sound board ?

    I usually do the head and tail blocks first, then work around a bout at a time.
    THE WORLD IS A BETTER PLACE JUST FOR YOUR SMILE!

  22. #19

    Default Re: how to remove epoxy on the top sound board ?

    I have a set of 12 4" clamps, just a bit too small for the cello. By removing the 4" stop, they open up to 4"3/4, I use epoxy at the end to create a "stop" point so I don't accidentally pull it out.
    12 clamps are enough to work on this. I start from the head block, using weak HHG (HHG with more water than usual).
    Click image for larger version. 

Name:	sm8.jpg 
Views:	33 
Size:	203.1 KB 
ID:	165420

    Just a quick question: how long is the minimum clamp time ? (before I move to the next section).

  23. #20
    Registered User
    Join Date
    Jan 2009
    Location
    S.W. Wisconsin
    Posts
    4,469

    Default Re: how to remove epoxy on the top sound board ?

    If you had more clamps I would keep going, but since you don't I would wait overnight or 24 hours.
    THE WORLD IS A BETTER PLACE JUST FOR YOUR SMILE!

  24. #21
    Adrian Minarovic
    Join Date
    Oct 2003
    Location
    Banska Bystrica, Slovakia, Europe
    Posts
    2,224

    Default Re: how to remove epoxy on the top sound board ?

    Quote Originally Posted by kkmm View Post
    Just a quick question: how long is the minimum clamp time ? (before I move to the next section).
    I would give it 4 hours if your temp/humidity is good and plate fits well and I'd leave the last two clamps in place while inserting glue close to the glued region so you won't accidentally open already glued parts.
    Adrian

  25. #22
    Registered User
    Join Date
    Jan 2009
    Location
    S.W. Wisconsin
    Posts
    4,469

    Default Re: how to remove epoxy on the top sound board ?

    Quote Originally Posted by HoGo View Post
    I would give it 4 hours if your temp/humidity is good and plate fits well and I'd leave the last two clamps in place while inserting glue close to the glued region so you won't accidentally open already glued parts.
    Good idea Adrian, I hadn't thought of leaving two clamps.
    THE WORLD IS A BETTER PLACE JUST FOR YOUR SMILE!

  26. #23
    Registered User Timbofood's Avatar
    Join Date
    Mar 2007
    Location
    Kalamazoo, MI.
    Posts
    6,604

    Default Re: how to remove epoxy on the top sound board ?

    I believe the gap between the top and rims is called a “separation” since it’s a joint failure(which is meant to happen so, the top does not develop a real crack, didn’t work on this one, apparently) but, that’s splitting hairs. But, I digress, I agree with Adrian about the “keep the separation from expanding” clamp technique. Here you have another opportunity for learning!
    Considering the “Gorilla Glue Debacle” I’d say you’re doing well!
    Have you learned a lot from this project.
    Timothy F. Lewis
    "If brains was lard, that boy couldn't grease a very big skillet" J.D. Clampett

  27. #24

    Default Re: how to remove epoxy on the top sound board ?

    Maybe its the perspective, but kinda looks like a beached whale sitting there in your garage on it's back.

  28. The following members say thank you to Jeff Mando for this post:


  29. #25

    Default Re: how to remove epoxy on the top sound board ?

    I just learned something new. By gluing from the neck toward the tail block. The top plate got off-centered at the tail.
    So I remove the top again, (proof that the glue is weak), clean all the HHG residue with hot water.
    Now I start from the tail block. The top at the neck simply can't move out of position as it has a notch right there.
    I should have figured this out before doing any gluing.
    I checked and there is no gap between the top and the rim all around by doing a dry run (clamping around without glue).
    This time, it should be OK. A few more days and I should be able to string it up and try.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •