Guitar Shop with Guitar ER

The Doc is in;
This month Chip's and Dip, but not the ones you eat.

Doc; I have a problem. The other day when I was done playing my guitar I didn't quite get it all the way in the case and the top of the case came down and hit the top of my guitar. It put a big dent in it and scratched the top. What should I do? I don't have the money to refinish the top. P.S. My guitar is a Martin HD-28 that is not more than 6 months old. Please help, Mike S.

Mike,
You have been Chipped and Dipped and I will try to help with your problem. First off lets talk about finish repair. Repairing a finish is more difficult than putting on a new finish. You will need to know a lot about the finishes that are used on guitars to help you in the repair. Unlike many other repairs on guitars, you can learn finish repairs by practicing on other things like, old guitars from garage sales, old clocks, furniture, ceramics, items with epoxy finishes, many different items can be used to practice on. You can get really good on these old items before you ever touch your valuable guitar.

Now lets talk about the three most common finishes used on guitars. Since spraying techniques have improved so much over the years, this is the main technique used by most all manufacturers, and lacquer is the most notable being used by Martin, Gibson, Fender (up until the mid 60's), Gretsch, and Guild. Many modern guitars, especially electrics, are finished in polyurethane, polyesters, epoxies, etc. These finishes don't redissolve or melt in like lacquers do and are hard to rub out, but you can do a lot with them. But it is best to know which finish has been used on the guitar you have so you can understand the different workability of the product on your guitar, and which guitar you should work on and which you should not.

Shellac or varnish was and is used on expensive handmade guitars, (especially classical and flamenco guitars). Shellac or French Polish, was used on most American made guitars prior to about 1930. French Polish is a method of applying a finish and not the finish itself. Although French Polish is an important technique for finish repair, it is beyond where we need to be at for this repair. I don't advise you to work on French Polish (shellac finish) because they are hard enough to clean, and harder to work on. Plus no do it yourself work allowed on vintage guitars.

Lacquer finishes (as on your guitar) are found on most acoustic and many electric instruments made since 1930. But more recently guitars with lacquer have a thicker finish and are easier to work with than vintage finishes which are thin, dry, and brittle and take very little sanding before you sand through the finish into bare wood. Lacquer is the easiest to repair because it will melt into itself (redissolves itself) even after years it will build up when drop filled (using a small amount of lacquer to fill a scratch), and this is a real advantage to lacquer finish repair. Always be careful around lacquer finishes because they can be dissolved by or touched by super glue, lacquer, shellac, alcohol, and lacquer thinner, which any can be used to repair a lacquer finish. In your case we will use nitrocellulose lacquer.

Now if the finish looks as though it has been dipped in a vat of liquid it most likely has a poly finish on it (polyester, polyurethane, or a urethanenamal). These finishes, which are found on most imports and American made electrics made after the mid 60's. Once these finishes dry
they are very hard and when cured no solvent that I know of will soften them, which means it will not dissolve or melt into itself. So with this in mind it makes it almost impossible to make invisible repairs (though it can be done). So for touch-ups use super glue.

Now back to your guitar. Supplies you will need. Lacquer and lacquer thinner. You will need to go to a local guitar or furniture repair shop and see if you can buy a small bottle of nitrocellulose lacquer from them. (It mostly comes in gallons and quarts and that is way more than you will need). Also Naptha (lighter fluid will do), this is good for cleaning the area around the repair so you can get all the oils off the finish. It works well on lacquer and all guitar finishes. Also you will need to go to an auto body supply store to get wet/dry sand paper as well as rubbing compound. Finally you will need a clean, soft dry cloth for polishing (old clean baby diapers work well or cotton flannel). Buy plain untreated flannel with non color (white). For sand paper I use 800 grit finest paper for leveling and 2000 grit wet /dry paper (I use it wet). Also you will need a straight edge, razor blades, single sided, and scotch tape.

Now since most dents create a low in the finish, your job is to fill in the dent let it dry, level, and polish. FIRST practice on an old guitar or a piece of old furniture so you have it down perfectly before you every touch that HD-28.

For those of you that want to determine what type of finish you have on your guitar before you attempt to repair it, here is what you do. To test the finish on most guitars you can remove the tuners or on electrics remove the plate to the controls. For the control cavity you can use lacquer thinner or alcohol and if it softens the finish you have a lacquer or shellac finish but if it does not soften or even melt the finish you have one kind of a poly finish.

Before beginning the repair, clean and degrease the area with a rag dipped in the naptha and allow a few minutes to dry. Next you will use the lacquer to drop file the dented finish area by using a tooth pick or a very small brush, dipped in the lacquer and dropped into the finish dent (hence drop fill) until the build is level with the finish on the guitar. It will take more than one drop to fill as when lacquer dries it shrinks so usually more than one drop will is needed. The lacquer will melt into itself but thinner (a little in the lacquer) speeds it up and makes for a better melt in. Let it dry for a couple of hours then drop fill with unthinned lacquer, then let it dry overnight or until it is hard and clear. When using a brush to drop fill and repair scratches DO NOT paint the lacquer on to the finish, use the brush to set a drop of lacquer in the dent, as I said it may take a few drops to fill the hole. Do Not rush this part of the repair; let the lacquer dry between the coats. Now after the hole is filled you can level the drop fill. I use a single edge razor blade with scotch tape used to cover the blade ends. (Wrap it around the edge of the sharp blade one time
to act as a scratch guard and lubricant for the blade). Now use the blade as a scraper to level the drop fill. Once the drop fill has been lowered you can now use the 800 grit sand paper to level the rest of the lacquer to the height of the finish around it. (Do Not use a lot of pressure when sanding. Be patient). Then go to the 2000 grit wet dry sand paper (All wet/dry sand paper should be soaked overnight in water so the paper does not load up with finish when sanding and it also works as a lubricant) One piece of sand paper can last a long time this way. Now I use a rubber eraser as a sanding block and sand out the marks from the 800 grit paper. Once this is
done you can move on.

Now follow with one or two grades of mirror glaze compound (#2 and #9). You can get this at your auto supply store. Begin your rub out with #2 and progress to #9. Use a clean baby diaper or cotton flannel for the rubbing. Do not use too much pressure when rubbing as you can rub through the finish. Also rub with the grain in the wood and start your rubbing 3 to 4 inches beyond the area you want to polish to blend it in and stop when the gloss has come back. To finish the job you can use Mirror glaze #7.

You're done we hope. Now this is a job that is not for your every day Joe, so if you have finish problems it is best to go to your repair person first to get an evaluation on your guitar and his or her advise on whether this is a repair you should be attempting, since a finish can be harmed very quickly if not done properly.

Also if the wood in your guitar has been crushed or dented this is one way to try to swell it back. Dents that have crushed wood fibers can usually be swollen back out without steam. You are going to lose the finish in that area but most likely the crushed wood will come back. Because the finish has to be removed in order to introduce water to the wood. After chipping away the finish, dampen the wood with a rag dipped in water and leave the damp rag on the dent. Then use a soldering iron or pen to swell out the dent. BE CAREFUL as you can harm the finish and wood with the heat.

All these ways to fix your guitar are some that we use in the shop but not all of them. We have many special tools and finishes to work with but as a backyard repair this can hopefully help you out. If you have any question see your local repair person or drop me a line or give me a call.

Until next time, keep the toes tappin and the fingers dancing. If you have any questions for the Doc you can email him at greg@theguitarer.com or give him a call at 515-707-4878. Greg/Luthier/Doctor

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