Cracked poly finish

If you have a string instrument of any kind that needs fixing, a mistake you made in building a new instrument that you need to "disappear," or a question about the ethics of altering an older instrument, ask here. Please note that it will be much easier for us to help you decide on the best repair method if you post some pictures of the problem.
Post Reply
John Clifford
Posts: 180
Joined: Mon Dec 18, 2017 3:08 pm

Cracked poly finish

Post by John Clifford »

I recently acquired a Parker Fly with a crack in the finish that's been there for several years. I think they used some kind of poly finish. It's more plasticy than lacquer. I'm not worried about how it looks now, but the edges of the finish seem to be getting a little loose and starting to peel back along the crack, and I'm worried about it delaminating or flaking off at some point. I would like to do something to stabilize it, if that can be done without making it look worse. I'm thinking about wicking in some thin CA glue, maybe with a needle injector, but I don't know much about poly finishes. If I get some CA glue on the top, how do I clean it up? Any ideas?
Attachments
Fly finish crack.jpg
Joshua Levin-Epstein
Posts: 244
Joined: Sun Jan 08, 2012 7:58 am
Location: Massachusetts

Re: Cracked poly finish

Post by Joshua Levin-Epstein »

Many of the synthetic finishes I've encountered aren't affected by acetone. Find a hidden spot and try both the CA and acetone. You might be able to clean up with the acetone.
User avatar
Barry Daniels
Posts: 3223
Joined: Thu Jan 05, 2012 10:58 am
Location: The Woodlands, Texas

Re: Cracked poly finish

Post by Barry Daniels »

Yep, CA and clean with acetone.
MIMF Staff
John Clifford
Posts: 180
Joined: Mon Dec 18, 2017 3:08 pm

Re: Cracked poly finish

Post by John Clifford »

Thanks guys. I think I can try it out on an area under the cover plate in back, so that's the plan.

What do you think about clamping? I was thinking I could place 2-3 layers of masking tape along both sides of the crack and lightly clamp a flat caul across those, bridging the crack itself so I don't end up wicking CA under the caul. On the other hand, maybe that's not necessary. The paint still looks pretty level, but I can hear a difference in tone as I tap lightly about 1/4" from the crack, so I know it's coming loose in that area.
David King
Posts: 2690
Joined: Sat Jan 07, 2012 10:01 pm
Location: Portland, OR
Contact:

Re: Cracked poly finish

Post by David King »

I wouldn't try to do anything to hold down the edges. Let the CA fill in underneath and leave it alone for 8-12 hours. Use a fine pipette or whip tip and keep paper towel handy to mop up the edges. Wipe across the crack with acetone to clean up any residue on the surface after the glue has set up.
John Clifford
Posts: 180
Joined: Mon Dec 18, 2017 3:08 pm

Re: Cracked poly finish

Post by John Clifford »

Thanks David. I'll probably try it that way.
Chuck Tweedy
Posts: 1182
Joined: Fri Jan 06, 2012 6:25 pm
Location: San Diego, CA

Re: Cracked poly finish

Post by Chuck Tweedy »

thin CA will wick under masking tape and cauls. You want NO features for it to crawl under - just the crack.
Likes to drink Rosewood Juice
John Clifford
Posts: 180
Joined: Mon Dec 18, 2017 3:08 pm

Re: Cracked poly finish

Post by John Clifford »

I’m sure you guys are right. Thanks for the guidance.
John Clifford
Posts: 180
Joined: Mon Dec 18, 2017 3:08 pm

Re: Cracked poly finish

Post by John Clifford »

I followed the excellent advice given above, and it worked out great. No "after" photo, because it looks the same as before, which is exactly what I wanted.

So thanks again. I really appreciate this resource.
Post Reply

Return to “String Instrument Repair: Practical and Political Issues”