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| Varnish repair for acoustic guitar http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10137&t=51737 |
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| Author: | stringsfire [ Tue Mar 19, 2019 8:45 am ] |
| Post subject: | Varnish repair for acoustic guitar |
Hi, I have a Fender F210 and I wished to replace the bridge, so I managed to remove the old piece but in doing this I also removed part of the varnish. Now before glueing the new bridge I wanted to restore the varnish where it is missing. Which product should I use? Is that a particular kind of resin? Here's a picture  Thank you for your help! |
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| Author: | Freeman [ Tue Mar 19, 2019 10:51 am ] |
| Post subject: | Re: Varnish repair for acoustic guitar |
1 - the finish that Fender uses is some sort of a catalyzed poly(something) - there are different formulations but the short story is that most of us aren't able to repair them. 2 - the area under the bridge should have the finished removed so that you get a good wood-glue-wood interface. The glue most often used is AR (Original Titebond) - it does not bond well to any kind of finish. You need to remove the finish to match the foot print of the bridge, the glue and clamp your new bridge tightly to the top 3 - I use ordinary paint stripper to remove finish but it doesn't work very well on the catalyzed stuff Fender uses. You'll probably have to do a lot of scraping and sanding. 4 - in my opinion, Fender does a lousy job of preparing their tops for the bridge glue up - I have repaired three different guitars where that joint failed and it was obvious that Fender simply had not prepared the surface. In fact one of those guitars was brand new and hanging on the wall of a music store. Oh, and when the store owner sent a picture to Fender they said "thats the way we do it" and it wasn't under warranty. |
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| Author: | Bryan Bear [ Tue Mar 19, 2019 11:23 am ] |
| Post subject: | Re: Varnish repair for acoustic guitar |
There is currently a thread here where Hesh (a repair pro) talks about gluing to wood vs. gluing to finish. Traditionally, I think, most of us think that the bridge should be glued to bare wood (with a perfect fit for a good glue joint) but Hesh challenges that under certain circumstances. He said that gluing to the correct type of finish, one that will not be able to de-laminate from the wood is an acceptable option. I am far from educated on the different modern finishes so I won't comment here beyond pointing out that 1) that finish did not adhere perfectly and 2) you probably aren't set up to repair the finish with whatever product would be appropriate. I would be thinking about cleaning the finish off and getting a good fit with the bridge and glue wood to wood. There are lots of different approaches for this too. There are TONS of discussions here, do a search and read as much as you can before you settle on a plan of attack. |
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| Author: | jfmckenna [ Thu Mar 28, 2019 7:28 am ] |
| Post subject: | Re: Varnish repair for acoustic guitar |
I believe the very few people that actually do glue directly to the finish do so with CA glue. You don't have a problem with the finish on that guitar. IOW you don't need to fill in what you need to do is remove. Clamp the bridge in place. You can use two 3/32nd inch screws and wing nuts through the outside pin holes. Then with a brand new and VERY sharp exacto blade score a line around the bridge through the finish. Be very very careful not to score the wood. You don't even really need to go through the whole finish. Then with a chisel 'lift' the finish off and it will snap right at your scored line. IF it doesn't lift off that easily then scrape it off with the chisel or something like a razor blade. Get down to bare wood around the whole bridge foot print. If you do it perfectly the bridge will 'snap in' place. Then glue it in place with Tightbond. You can use screws as clamps again but you will need clamps anyway for the wings and it's best to make a clamping caul for the inside of the guitar too. |
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| Author: | Conor_Searl [ Thu Mar 28, 2019 11:07 am ] |
| Post subject: | Re: Varnish repair for acoustic guitar |
jfmckenna wrote: Then with a brand new and VERY sharp exacto blade score a line around the bridge through the finish. Be very very careful not to score the wood. You don't even really need to go through the whole finish. Then with a chisel 'lift' the finish off and it will snap right at your scored line. IF it doesn't lift off that easily then scrape it off with the chisel or something like a razor blade. Get down to bare wood around the whole bridge foot print. This is what I've been doing too. A secondary caution to go with not scoring too deep, you need to score deep enough that the finish will break off at the scored line when you chisel otherwise you'll end up with finish chipping off outside of the bridges foot print. |
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| Author: | Bryan Bear [ Thu Mar 28, 2019 11:16 am ] |
| Post subject: | Re: Varnish repair for acoustic guitar |
If going the rout of removing the finish under the bridge footprint and re-gluing (that is what I would do), it should be mentioned that the underside of the bridge should be prepared for the glue up as well. From the picture, it looks like some spruce came up and is probably still attached to the underside of the bridge along with the finish that came off. That should be removed from the bottom of the bridge before re-gluing. |
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| Author: | Hesh [ Sat Mar 30, 2019 12:19 am ] |
| Post subject: | Re: Varnish repair for acoustic guitar |
1). Use the original bridge to trace the foot print JUST inside the foot print with a single edged razor blade scoring through the finish NOT the top wood. 2). Use a very sharp chisel to remove all finish up to your score marks. I score finish very close to the bridge perimeter with the goal being to greatly expand the wood to wood gluing area. I may be .010" from the perimeter at times, that close. 3). Clean up the bridge bottom of all old glue and finish. I use a belt sander where I know my platen is flat. 4). Trial fit the bridge to the top. Be sure any internal issues are addressed so the guitar's top is not distorted from say a loose brace. Inspect the bridge plate for cracks. If the bridge needs more than finger pressure to be down everywhere including the wings I fit the bridge to the top. My method of fitting is to scrape the bridge bottom with a razor blade to match the top trial fitting, adjust, repeat, etc. 5). When the bridge is fitting well do a dry run with your clamps to be sure that you have all that you need, i.e. internal caul, waxed paper, proper clamps that reach the wings and center, etc. 6). I would use Titebond original if you have a decent bridge fit with clean wood to wood surfaces. Not going to advocate HHG for a one time repair foray because of the overhead, learning curve, need for stuff you don't have, etc. Same goes for rabbiting. 7). Scrape the bridge bottom and bridge patch on the guitar top just prior to gluing and clamping. Wait 24 hours before exposing to string tension. If the top is very damaged and the guitar is a POS a quality epoxy can be helpful. Hope something here helps. |
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