Official Luthiers Forum!
http://www.luthiersforum.com/forum/

Big oops on build #1`
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=19184		 Page 1 of 1
Author:  Mark Ewing [ Mon Oct 13, 2008 9:12 pm ]
Post subject:  Big oops on build #1`
I was buffing the frets as the very last thing to finish my first build and low and behold I found a three inch scratch on the top. gaah Don't ask! When I saw it I about fell over. So I'm looking and I think to myself. This is superficial. It's only in the finish, so I tried buffing it out. Wouldn't you know. It was not superficial. I buffed down to the wood. oops_sign It is bear about the size of a quarter.
So what's a rookie to do. idunno Can I fix this without refinishing the whole top or is that the way I need to go? It is a lacquer finish.
Author:  Cal Maier [ Mon Oct 13, 2008 9:33 pm ]
Post subject:  Re: Big oops on build #1`
My first thoughts are to refinish the top. If you've gone down to bare wood you will most likely get witness lines if you try to touch-up.

A picture would help, and also the type of finish that you've used, but unless it's french polished shellac I would prepare to refin.

Cal
Author:  Tai Fu [ Mon Oct 13, 2008 9:50 pm ]
Post subject:  Re: Big oops on build #1`
You don't have to refin though, you can spray more coats of lacquer over it, but first soften the lacquer with some blush eraser or something to allow the lacquer to blend into itself. Clean the remaining polish off of the wood first though. Or else you can just leave it... it's not gonna affect the sound anyways.
Author:  Kevin Gallagher [ Mon Oct 13, 2008 9:53 pm ]
Post subject:  Re: Big oops on build #1`
Mark,
What finish did you use? If it's lacquer, you can easily touch it up in that area with absolutely
no evidence of the repair. Other finishes may leave faint witness lines as the new coats simply
lay on top and have to be feathered in at the edges, but lacquer will actually melt into the old
coats and become one with them.

Once it has cured, you'll simply level and buff again....but much more carefully as to avoid
getting to the wood again.

Regards,
Kevin Gallagher/Omega Guitars
Author:  Martin Turner [ Mon Oct 13, 2008 10:21 pm ]
Post subject:  Re: Big oops on build #1`
Hey Mark, if it makes you feel any better. I finished reading your post and then went out to my workshop and dropped my Stewmac thickness caliper on the floor. Guage is wrecked and Im halfway through thicknessing a back for a classical. oops_sign
Author:  Mark Ewing [ Tue Oct 14, 2008 4:21 pm ]
Post subject:  Re: Big oops on build #1`
Kevin Gallagher wrote:
Mark,
What finish did you use? If it's lacquer, you can easily touch it up in that area with absolutely
no evidence of the repair. Other finishes may leave faint witness lines as the new coats simply
lay on top and have to be feathered in at the edges, but lacquer will actually melt into the old
coats and become one with them.

Once it has cured, you'll simply level and buff again....but much more carefully as to avoid
getting to the wood again.

Regards,
Kevin Gallagher/Omega Guitars

I used lacquer. So let me guess about the process. Tape off the areas I don't want coated. I use an HVLP, so I would spray the area with a bit of overlap or should I re-spray the whole thing. It thought I should put a little lacquer thinner in so it would "burn in" a little? Or would it be better to scuff sand to get a mechanical bond? What say you?
The other question is how many coats?
Thanks
Mark
Author:  stan thomison [ Tue Oct 14, 2008 6:39 pm ]
Post subject:  Re: Big oops on build #1`
you don't have to respray the whold top. can, but don't have to. if to wood and had color,well have to match the color/tint. like todd said can use touch up gun if have one or do a drop fill type thing and work it in.
Author:  Kevin Gallagher [ Tue Oct 14, 2008 6:54 pm ]
Post subject:  Re: Big oops on build #1`
Mark,
With lacquer...here's what I would suggest. Sand the area surrounding the open spot to 1000 grit. There will be no mechanical
bond, but a chemical bond so the sanding doesn't serve any other purpose than to provide a nice smooth area for the new finish
to lay. I'd mask the guitar completely outside of of the area of about four or five inches in diameter around the open spot and
then tighten the spray pattern on you gun, pull back the material delivery and spray the first two or three coats right on the spot
with a few bursts without swinging a spray stroke.

Before you point and shoot those focused, concentrated lacquer bursts on the top of the guitar, do a few quick spots on a test
piece to get familiar with how your gun and the materials you're shooting will respond. The key to these coats is to keep them light
and allow them to build up. in the bare area. They will burn into the existing finish and will actually become one with it.

This will allow a nice concentration of material in the bare area to start. Let those coats set up for a day or two and sand them to 600 or 1000 grit and do the same, but in a slightly larger diameter pattern. You should be able to see a material buildup now and allow that second set of coats to sir for another few days.

Level those coats carefully as not to break through them again. Be sure to draw the edges into the existing finish and there should be no visible witness lines at this point.

Spray a single light coat in a diameter that allows two or three inches outside of the open area and allow it adequate time to cure and shrink before treating it like the finish was originally brought to its current gloss or patina.

Any overspray should be pretty easily addressed and any indication of the repair can be worked out to be nonexistent. Lacquers are some of the most forgiving and reworkable finishes available. I've rerouched hundreds of guitar with lacquer finishes to a point
where the repairs were invisible. Some finishes are very difficult to work in a repair situation where there are no witness lines, but most can be very effectively touched up without the need for recovering an entire surface like a top, side or back.

Let us know what you decide and how it goes.

Regards,
Kevin Gallagher/Omega Guitars
Author:  Mark Ewing [ Tue Oct 14, 2008 8:29 pm ]
Post subject:  Re: Big oops on build #1`
What you have shared has given me hope. I worked really hard on the finish and it came out pretty good for a first timer. Here is a picture of the oops. I will post a refinish picture. You all have helped me in so many ways. Thanks.
Mark
Author:  Kevin Gallagher [ Wed Oct 15, 2008 5:20 pm ]
Post subject:  Re: Big oops on build #1`
Mark,
That's in about the best possible spot to deal with it. There's is lots of landscape in every direction to work the new finish
into the original.

Keep us posted on the repair. I'm sure you'll do a great job and the guitar will be the instrument you dreamed it would be
when you get it done.

Regards,
Kevin Gallagher/Omega Guitars
Author:  Steve Davis [ Wed Oct 15, 2008 5:33 pm ]
Post subject:  Re: Big oops on build #1`
so was this nitrocellulose or water based ?
Do they both qualify as laquer?
How is the process any different on an older instrument with more aged colour
Author:  Tai Fu [ Wed Oct 15, 2008 7:23 pm ]
Post subject:  Re: Big oops on build #1`
On the subject of oops... I glued up the fretboard today. After allowing the glue to dry for about 8 hrs or so, I turned the truss rod to see if it works. Then I hear a sickening crack and the fingerboard at the first to 5th fret separated! So I turned the truss rod to widen the crack then used a knife to put more hot hide glue into it (good thing is that hide glue will melt into itself so no need to clean off the old glue) then clamped it tightly shut. It works fine now but I hope it will hold up. I think the problem is that I did not use enough glue at that end of the fretboard because I was so afraid of the glue getting into the truss rod slot.
Page 1 of 1 All times are UTC - 5 hours
Powered by phpBB® Forum Software © phpBB Group
http://www.phpbb.com/