Re-finishing a french-polished red cedar soundboard and damage repair

[Christian Schwengeler]

Hi all,

I am going to refinish a cedar top which has plenty of scratches on it. I have done it before and I find this always a challenge. If you sand the scratches out this may leave some blotchy spots with different stain and I find always, when I look to a refinished top in an angel against the light, that you can see that it is refinished and where the problem spots and damage were,no matter how flat the finish is.

I find this with red cedar particularly challenging. I use clear super blond shellac but I have the impression that even if you sand the old finish all off it will be never the same as a new fresh finish on new wood. So in this case it makes no sense to sand it all off. It is also sound wise a risk as I may thin out the sound board what I do not want. I am not a repair man but I build mostly new instruments so I have limited experience with refinishing. I would like to have your advices about the subject: How can you efficiently eliminate scratches and damages like nail marks and refinish a French polished cedar-top without making it look refinished but rather like new? I have seen professionally restored red cedar instruments on pictures like Friedrich and others which look also pretty ugly when you hold them against the light. Is there no other way or is this just leak of knowledge of the person who did the refinishing job?

Can you use pumice to eliminate scratches for example? One professional finisher on an other forum mentioned once that he sees the French polish rather in the perspective of an Ice block and that he would rather use alcohol to level the surface by melting and redistributing the shellac. What do you think about this procedure? He said that he would never sand a French polished surface. But when I read the general experience of the other luthiers on the forums I see that nearly all do sanding. Just tell me about your experience, if you feel so.

[Waddy Thomson]

Scratches, if not too deep can be filled with pumice, alcohol, oil and a touch of shellac. It sometimes takes a lot of work to get it done, and you can't concentrate on one area too much. Deep intentions can, sometimes, be steamed out, right through the polish. You still have to re-build the finish in those areas, however, and it may require some very light sanding to get rid of the raised grain. These days, however it's a good idea to know what shellac was used, as if you get a guitar that has been finished with the U-Beaut, you would probably have to lightly sand the entire top to give a workable surface for new shellac to adhere. With regular, old shellac, you can spirit/stiff off the gloss with alcohol, then start refreshing the finish from there. If the guitar is more than 5 years old, it's not likely to have U-Beaut on it.

[Michael Lewis]

It is very easy to make a cedar top look worse by trying to make it look better. There are a few things you need to do: get all the dents and scratches out, this usually means block sanding the entire surface (remove the bridge); smooth sand and raise the grain; apply new finish and reglue the bridge. It sounds simple enough but is quite a task to get it right.

Is the top so ugly that you can't stand to play the guitar? Or does the guitar now have 'character' ? They are new only one time, after that they are used, and eventually vintage. The older the instrument the more wear it is allowed to have.

[Christian Schwengeler]

Hi again,

thank you both for your very kind and usefull returns. The guitar is one of my own build, it is from a client who did resell the guitar to a student. The problem is that the professor did scratch up the guitar pretty bad allready in the first few month. So the student who bought it wants it to look better. I share the opinion that it is no shame when an Instrument looks used, but the owners are sometimes very considered how it looks, so I have no other way than to accept the job. Th top was french-polished by myself with superblond dewaxed shellack and the instrument was beautifull when it was new and I was somewhat surprised to find the instrument in pretty bad shape allready a few months later..

best greetings and thanks

Christian

[Michael Lewis]

One idea pertaining to finish repair is that hard or brittle finishes like shellac and some lacquers will fracture or powder when dented or scratched, and this fracturing causes the area to look very light in contrast to the surrounding area. A small brush to apply the appropriate solvent will wet the fractures and remove the light appearance, and actually melt the surfaces of the tiny powdered pieces of finish back together. This goes a long way toward 'fixing' the damage, and makes the scratches much less noticeable. For shellac use alcohol, and for lacquer use lacquer thinner or any one of several solvents (MEK, acetone, etc.). This does not swell the compressed wood fibers, for that you need water and heat. But that process can easily make things go from bad to worse very quickly.

[Chuck Tweedy]

I agree with Michael's suggestion to try a general re-application over the affected area.
I had a very similar case of a customer who requested a top refinish for pretty minor scratches. I asked if I could try a "local" repair before stripping the whole top.
It was (is) a Spanish flamenco of considerable value, and I really had no business at all re-finishing the top, so I was really hoping this would work.
Not sure what the finish really was, so I puckered up the courage and started French polishing right over the scratches. It worked fantastic - just like Michael described. The scratches quickly took on the color of the surrounding finish, and the polishing process rounded and muted the edges of the scratches.
From a few feet away it was very difficult to see where the scratches were. There were also belt buckle scratches on the cypress back - an those disappeared even more magically.
When I was done, the customer accepted it as done and did not request I strip it (Whew!)
Then I built him a new guitar. That one paid off.

[Christian Schwengeler]

Thank you again for your replies. I have started the job and until now it is easier than I expected. I use a little pumice. I have filled the bigger dents with heavy cut shellack and have used 00000 steal-wool to level locally when needed. Well lets hope that everything goes smooth until the end.