How to Detail a Classical Guitar

The quality of any finish will depend greatly on how well the classical guitar is detailed. The finer the finish you are going to use, the more any defect will show. Our purpose is not to teach wood working so we will assume that the guitar is well scraped, sanded and with all gaps filled. All of the purflings and bindings should be perfectly level and flush.
Detailing the guitar edges with a sanding "stick".
The back, sides, and top of a classical guitar should be as level as possible with all the inlay work, including the rosette, flush to the touch. Remember, you will create extra work for your self if you find a defect after you are well into the finishing project. Visually examine the instrument for areas of discoloration, nicks, scratches, and any other defects. When satisfied with your examination, wipe down the entire guitar with naphtha solvent. You will be surprised at the number of defects that will show that you didn't realize were there. These are the same defects that will show up when you begin to French polish. One of the advantages in using naphtha for this purpose is it's very slow evaporation rate. You should have plenty of time to mark, very lightly, the areas that need attention. Sand all of the marked areas with 220 grit open-coat dry sandpaper. The 220 grit sandpaper is not aggressive enough to change the thickness of the top of the guitar. A moderate light sanding should be enough to remove a minor scratch or defect without the danger of changing the instrument's tone quality. If, by chance, you discover a large dent or scratch that might require excessive sanding you may want to steam the defect before trying to sand it out.
Using cyanoacrylate adhesive (SuperGlue) to fill small defects in the rosette.
At the very least you will reduce the amount of sanding that would have been required. To steam out a defect, dampen the area and lay a wet cloth only on the spot that you are going to steam. With a clothes iron turned all the way up, lay the iron over the wet cloth covering the defect and hold for a few seconds. Let the area dry and a little light sanding with 220 grit dry sandpaper should do the trick. A deep nick will usually have to be filled with a dent filler such as cyanoacrylate (SuperGlue) or epoxy. A major nick or gap can be filled with sanding dust mixed with 5 minute epoxy. When sanded level, this will make a good invisible repair. Be sure to check over all of the surfaces for small areas of discoloration before the naphtha solvent has evaporated. When perfectly satisfied with your results, clean the guitar using only a damp cloth. This will remove sanding dust and slightly raise the grain. This will also raise any ridged areas that were not noticeable while using naphtha solvent. After the moisture has dried from the guitar you then can sand all of the surfaces with 400 open-grit dry sandpaper. After this final sanding, wipe down all of the surfaces with naphtha solvent and let completely dry.