- What Caused My Acoustic Guitar To Crack?
- Repairing Cracks
- Cracks That Will Not Close
- My Guitar Cracked, Now What?
- Lacquer Cracks
- Scratches in your Guitar’s Finish
- Bubbled Guitar Finish
- De-laminated Guitar Finish
- Yellowing Guitar Finish
- Drop Filling Acoustic Guitar Dents or Chips
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What Caused My Acoustic Guitar To Crack?
A washboard texture which looks somewhat like corduroy is one of the first signs of dryness.
It is very important that you know how to recognize this and what to do about it should your guitar start to show these signs of dryness.
In the picture below the soft spruce top has lost a great deal of moisture and the dark grain lines now stand prominent, the ridges are noticeable to the touch.
Cracking is likely if the problem isn’t addressed and its dry season continues.
A dried out spruce top often
Tops are build with radius or arch. As the instrument dries out this arch will flatten and the washboard texture may already be noticeable.
If humidity is low and the instrument continues to dry out the arch will flatten and can become concave when terribly dry.
If your instruments top begins to dip and become concave without cracking you’re pretty lucky, now is the time to begin humidifying.
The majority of instruments that are truly dry will crack the top first , very dry instruments can also split along their sides or seam lines.
On one of those, a good rap or bump to the side can result in the side splitting wide open, not a pretty sight.
Common Signs of Dryness
- Washboard texture on top
- Lower action due to a flatter (dropping) top
- Sharp fret ends
- Loss of top or back arching
Straightedge reveals concave guitar top.
While some cracks are relatively easy to repair it’s important to realize that are often a one shot deal. When repairing cracks it is essential that the separated halves are well aligned and the work is done cleanly. Reversing a bad repair is far more difficult and expensive than having it done correctly to begin with.
When repairing most cracks I like to have a caul on the inside and outside of the instrument that keeps both sides of the crack aligned while gluing.
Cracks Near The Pickguard
Several manufacturers employed the process of attaching the pickguard directly to the bare wood of the top before spraying the instrument.
Unfortunately these shrinking celluloid pickguards can cause a problem. If they maintain a good grip on the top while shrinking it places formidable stress on the top. If the pickguard shrinks considerably a crack can develop on either side of it.
To repair these cracks the stress must be eliminated by removing the pickguard and reattaching or replacing it. In an effort to avoid a repeat, and keep the new adhesive from pulling up wood fibers if removed again, this bare area of wood beneath the guitar is usually sealed with finish. View a Martin Pickguard crack repair.
The real challenge to repairing most tight cracks is primarily with the finish. Stripping and refinishing the entire panel to render an invisible repair on a small crack would be overkill to say the least. Depending on the crack, finish repair may not be advisable or necessary.
Glued cracks still leave a small valley in the finish. When repairing cracks it is usually a two part process; repairing the crack in the wood, and then repairing the finish.
When repairing lacquer finishes a new lacquer «fill» is placed in the finish crack. This lacquer fill will begin to shrink almost immediately and a small depression is likely to appear, even after weeks of patient waiting. Lacquer is very high in solvents and it shrinks quite a bit. For this reason small chips, sink marks and cracks can reappear after a flawless repair days or even weeks after it has been done. I try and educate my customers to the nature of wood and lacquer so they understand what is possible.
Taylor guitar damaged by impact.
Cracks That Will Not Close
More often than not, cracks that have spread open and will not close with humidity are spliced, filled with a inlay of wood. This dilemma is usually only found on older, very dry instruments, perhaps something that was left in a very poor environment. But there are other causes that can create the need for a splice, like something that has been damaged and wood is now missing or an area that is under so much stress that closure is not possible.
A splice is an insert of wood, like a filler strip, that is inserted into the area that is open. If the crack that is being repaired does not follow a straight line but runs across the grain the splice is much wider as a symmetrical splice must be used.
What about just filling the crack with putty, wouldn’t that be easier? Oh my, would it! However, I don’t do it. Putty and wood filler is not an acceptable repair method in most cases. While there are obviously some repairs that may require it, wood should be replaced with wood. Putty will shrink and usually just doesn’t look right. Obviously on something very inexpensive, splicing or wood replacement can easily exceed its value.
My Guitar Cracked, Now What?
If there is any chance that the crack is related to dryness you should begin humidifying the instrument.
The best time to repair a crack on your instrument is before it has time to accumulate dirt and grime or worse, run like a bad pair of panty hose! (Sorry guys . a Pinto on Nitrous?) If string tension puts stress on the crack you should remove it immediately.
Cracks that go un-repaired can sometimes cause more serious issues, especially if it causes the wood to warp and twist out of alignment.
Cleats are normally made from the same material as the panel which they are reinforcing. While there are some repairs that require reinforcement, I avoid cleats unless absolutely necessary, especially on clean cracks. As I point out to my clients, every guitar has a top and back crack. tops and backs are made from book matched wood, two pieces of wood glued together down the center. This is a glued seam and is not cleated. (The center strip used over many back center seams is there to reinforce the area when the back is routed for a center strip.)
Whether caused by impact or dryness, cracks can effect the braces as well. The alignment, finish damage and ease of closure all contribute to the overall cost.
I offer free estimates to those desiring to have them repaired, I can not offer estimates based on pictures alone.
Acoustic Guitar Finish.
Your acoustic guitar’s finish can have all kinds of problems, as you play it over the years. Use and abuse of the instrument as well as the weather conditions ruin acoustic guitar finish. Unfortunately, unless you are going to keep your favorite Martin or Taylor in a vault, you will probably scratch or dent your guitar at some point. In this article, I’ll explain a few different guitar finish problems as well as a few ways to repair small finish blemishes.
Warning: Before we go on to learn about finish repairs, I urge you to think twice before experimenting with your guitar’s finish. Finish can be a tricky thing. In most cases, if you are not experienced, you will probably make the finish problem either worse or more noticeable. Do not practice on your prized guitar. Get experience on a $10 yard sale guitar. Then work on your real guitar.
Also, if you have a vintage guitar, I would suggest that you not tamper with the finish at all. A vintage guitar’s value will decrease drastically once it has been refinished. Trust me; in almost all cases, the vintage guitar will be worth more even with scratches and dents then with a new coat of finish. That being said, let’s repair your finish.
Lacquer cracks are generally caused by drastic changes in temperature or humidity. The lacquer is attached to the outside of the wood. While the wood can expand and contract with differing amounts of humidity in the air, the lacquer, for all practical purposes, cannot. This is the major reason behind lacquer cracks—the wood moves while the lacquer remains still. Most lacquer cracks start out small and internal, often called crazing or checking. These cracks look like hairline cracks, but cannot be felt when you run your finger across the top of the finish. The reason why the cracks feel smooth on the outside of the guitar is because the lacquer is cracking from the inside out. It’s cracking where it joins the wood. Some of these cracks will never materialize into an external crack, where as, others will. It just depends on how well you take care of your guitar.
Many vintage instruments have this sort of cracking, due to their age. If your vintage guitar has finish problems, think twice before you have it refinished. Refinishing a vintage guitar will decrease its value.
How to Repair Lacquer Cracks
You might think that these small cracks would be easy to get rid of. Couldn’t you just sand them down and buff the guitar out again? Unfortunately, the answer to that is no. Remember, these cracks are caused by the guitar wood itself and crack from the inside out. You can’t simply sand a little into the clear coat to get rid of them. Some of these small hairline cracks exist all the way down to the guitar wood itself. You would have to completely sand down the entire guitar to remove these cracks. Not only is this not worth the effort, it might be impossible if your guitar has any stain or burst on it.
Guitar lacquer is applied to the guitar after the color is sprayed or rubbed on. It would be nearly impossible to sand through the clear coat and leave the color completely intact. You will inevitably sand through some of the color and leave your finish with an uneven burst. This is a beginner mistake. Just don’t try it.
How to Prevent Lacquer Cracks
Since severe weather is what causes most lacquer cracks, preventing them is pretty easy. All you have to do is make sure your guitar’s environment right. Don’t let your guitar be exposed to drastic temperature and humidity changes. Don’t leave your guitar in a hot car in the summer or a cold car in the winter. And always, ALWAYS make sure to let your guitar acclimate itself to the conditions before you take it out and play it. When you play a winter gig and your guitar has to sit out in the cold car for a few hours, make sure to bring it inside a few hours before you open the case. This will give your Taylor or Martin a chance to thaw and acclimate itself to the new environment before going through the stress of being played. If you can manage all of that, you should have a difficult time getting lacquer cracks.
The guitar to the right is an extreme example of what can happen to your guitar if you leave it in a icy car and play it as soon as you bring it inside. It can start with a finish crack or completely crack the guitar top. Keep your guitar away from extreme weather changes.
Check out my acoustic guitar maintenance article for more info about proper humidity and temperature levels.
Scratches in your Guitar’s Finish
It is impossible to prevent your guitar from getting scratched up, so why even try? I’m just kidding. No one really wants their prized guitar to get all scratched up. Unlike lacquer cracks, finish scratches are caused by rubbing something on the outside of the guitar. These scratches usually only exist in the clear coat of the guitar. Although there is no real way to prevent getting scratches on your guitar other than never playing it outside of your living room, there are some ways of removing them.
Shallow scratches can be removed or buffed out of the finish in your guitar if you know how to do it. Deep scratches on the other hand, cannot be removed and will cause a bigger problem if you they to buff them out. Shallow scratches can be wet sanded, buffed, and polished again. These scratches look like small hairline scratches on the outside finish of your guitar.
To fix your guitar scratches, you can wet down a piece of 1,000-grit sandpaper with water and soap suds and lightly sand down the area with the scratch. Keep in mind, you only want to sand down a little of the topcoat of lacquer—nothing more. I usually start at 1,000-grit and work my way up to 12,000-grit sandpaper. Then take a buffing wheel or rag and work in some buffing compound. After the area has been buffed, you can polish it to a high shine. Keep in mind, if you are using a buffing wheel, you really only have to sand up to 2,000-grit. There is no need to go past that.
Once your guitar is polished, you shouldn’t be able to see any hairline scratches.
Deep scratches are scratches that you can feel with your fingertips or fingernail. These kinds of scratches are near impossible to sand out. They are too deep in the finish. If you go after a deep scratch with sandpaper, you will probably sand through the topcoat and into the color coats or raw wood like we talked about earlier. In this case, the guitar may need to be refinished to hide your sand through. Deep scratches are better left alone or brought to a professional. Do not try to fill these scratches with extra lacquer or other filler. Trust me. It will probably look worse than if you would have just left it alone.
Bubbled Guitar Finish
I just call this bubbled guitar finish. The finish doesn’t actually pop out like a bubble. It just looks like there is a bubble in the finish itself. This usually happens because the wood or materials under the finish shifted after the finish hardened. This commonly happens on the side of the unbound fretboards with finished necks. The shrinking of the guitar neck and fretboard try to pull the lacquer in as the wood shrinks. The frets, however, don’t shrink and cause the finish to crack or bubble and even crack. Usually bubbling is an early sign that a finish crack is coming soon. The easiest way to prevent these issues is the same as lacquer cracks. Take care of your guitar and try to keep the weather conditions consistent.
De-laminated Guitar Finish
This is not a very common event, but it does happen. Since the lacquer is sprayed on top of a clear coat or sealer coat, the lacquer is not actually attached to the wood of the guitar—the sealer coat is. This finish problem is most likely caused by a poor finish job. The topcoat is probably not sticking to the sealer coat. To fix this problem, you will need to strip the finish off the guitar and refinish it again. If you just spray more lacquer on top of the de-laminated finish, you will end up having the same problem later on. The problem is in the base coat—not the topcoat.
Yellowing Guitar Finish
Some guitar finishes like Nitrocellulous lacquer naturally yellow over time. This is a completely natural and completely unpreventable process. I talk more about this in my guitar finish article. Check it out.
Drop Filling Acoustic Guitar Dents or Chips
Unlike acoustic guitar scratches, guitar dents and chips are small in area and don’t sweep across the guitar body. In other words, you can easily fill them and not worry too much about ending up with inconsistent finishes across your guitar. Obviously, the guitar to the right is an extreme example with multiple chips in a row, but it is a good example. Here’s how to drop fill your acoustic guitar dents and chips.
Color the chip
Some acoustic guitars have a color stain or color burst around them. Some dents and chips take the color with when they are ripped out of the guitar. Before you put any finish on the guitar, you will want to make sure the color looks right. I like to put a small amount of acetone in a plastic cup and drop a few drops of color stain in it. This should mix up nicely.
Now you can dip a toothpick in the color mix and apply it to the chip in the guitar. The color mix should disperse over the dent. All you need is a couple drops of the color mixture. You can dab up the excess with a paper towel and let it dry.
Apply the Finish
Once the color stain is dried, you can put some finish on it. You can use almost anything from polyurethane, lacquer, epoxy, or super glue. All of these will work, but some take longer to dry and harden. Poly and lacquer could take as much as a day to dry. Epoxy and super glue dry much faster. I usually use super glue because it’s the easiest and fastest to use.
Drop a few drops of your finish on the colored chip. Make sure to get enough on there, so the drops of finish are higher than the old guitar finish. You basically want a bubble of super glue or other finish on top of the chip. Now just let that dry. You might have to do this a couple times to let the glue or finish build up. Make sure you do not use an accelerator to speed up the drying process for epoxy or super glue. Accelerators cause a chemical reaction that releases heat. You could bubble or ruin the surrounding finish this way.
Scrape off the Finish
Now that you have a large bubble of hardened finish on your guitar, you’ll need to scrape it off. The easiest way to do this is with a razor blade. This technique was popularized by Frank Ford. Take a razor blade and scrape it against a piece of metal until you get a nice sharp burr on one side of it. Then tape off the outer edges of the razor with regular, clear scotch tape, so the only part of the blade showing is a middle portion a little bigger than the size of your chip.
The next part is really cool. Place the razor flat against the guitar and run the un-taped blade against the bubble of finish. The burr on the razor blade will peel off the excess finish on the chip and the tape will protect the body from the rest of the razor blade. Lightly scrape the finish off until no more will come off with the razor. Notice the tape on the razor prevents it from scraping the spot flat against the rest of the guitar finish. You’ll need to hit the rest of this spot with sandpaper.
Sand the Excess Smooth
Sanding a small spot like this can be really tricky. You don’t want to go at it will a sanding block right away because you don’t want to sand down all the surrounding areas with course sandpaper. You should strip sand the chipped spot.
Strip sanding is pretty easy. Cut a piece of sandpaper into a 6 inch by .25 inch piece. Then place the sandpaper on the chipped area and press down with your index finger. Now pull the sandpaper with your order hand. This way the only part of the guitar that gets sanded is the chip and the chipped area.
When you strip sand the chip, you will want to sand in all different directions. Don’t keep sanding in the same direction. You’ll scratch marks in the finish that won’t buff out completely. Keep changing sanding directions. I like to start strip sanding with 400-grit sandpaper and work my way up to 1,000-grit.
After I have the chip strip sanded to 1,000-grit, I break out a sanding block and wet sand the spot with 2,000-grit sandpaper. If you use an actual sanding block, make sure to fully attach the sandpaper. I usually use a 1 square inch piece or rubber or hard foam that I double stick sandpaper to. Don’t fold the sandpaper over the edges of your block. You will get sand marks from the outside edges of the sandpaper. I like to use the sandpaper that has a sticky backing. That way I don’t have to bother with using double stick tape.
Wet sand the area with 2,000-grit sandpaper in a circular motion. Make sure to get the surrounding areas too—not just the chip. You want to work everything in. I usually wet sand all the way up to 12,000-grit sandpaper. Again, you don’t have to sand this high up if you are using a buffing wheel. 2,000-grit sandpaper would be sufficient.
Buff and Polish
Now all you have to do is take a rag with some buffing compound and buff the section. You can also use a buffing wheel. After everything is buffed out, grab a little cleaner and clean the rest of the guitar.
Your acoustic guitar should be looking great now! The cracks are buffed and the chips are filled. I hope this article helped you fix your guitar finish and get your guitar looking awesome. Now it’s time to play it. Just be careful not to get another scratch or dent.
by Kenny · Published December 29, 2011 · Updated August 12, 2017
If you own an acoustic guitar long enough, chances are good that you’ll have to deal with the repair of a crack in the wood. Knowing how to evaluate the seriousness of a crack will allow you to determine whether to call a repair person immediately or whether it might be OK to leave it alone for a little while. In this article we’ll take a look at how cracks form, how to evaluate the damage, and what a proper repair will entail.
WHAT CAUSES CRACKS
The main causes of cracks in your guitar’s body are low humidity and physical impact to the instrument. Low humidity causes the wood to shrink—we see a lot of these types of cracks in my Minneapolis shop during the dry winter months. Keeping your guitar storage room humidified as close to 45 percent humidity as possible or using a special guitar humidifier is excellent insurance against cracks caused by a dry environment (for more info on humidifying guitars, check out “It’s Not the Heat, It’s the Humidity,” from the February 2006 print edition).
Cracks caused by dropping or hitting the guitar can happen in many ways, and it doesn’t necessarily take a very hard impact. One classic crack occurs when you play sitting down with your keys in a pants pocket—if they press against the side of the guitar just right, voilà, a crack appears! Dropping the guitar in its case (especially an ill-fitting one that allows the guitar to move around inside) can do it, as can running into a mic stand or your partner’s guitar. Many guitar tops crack if the instrument is placed only halfway in its case and the lid slams shut; watch out for those latches! Another classic crack is the so-called “pickguard crack,” which is common on a lot of Martins built prior to 1985, when the company was still gluing its pickguards directly to the bare wood, rather than onto the finish. The pickguards on these guitars tend to shrink a small amount over the years, but due to their extremely strong adhesion, the top often cracks just behind the soundhole.
Sometimes what looks like a crack in the wood is actually just a crack in the guitar’s finish. Most often, this will be caused by the finish reacting to extreme cold or rapid changes in temperature, resulting in what’s generally referred to as “checking,” a weblike spread of damage (many modern polyester-based finishes are immune to this damage, but nitrocellulose lacquer can be very sensitive in this regard).
EVALUATING THE DAMAGE
How serious is it? The first thing to ascertain is whether your guitar is cracked all the way through the wood. Any crack in the wood is serious and can upset the delicate structural integrity of the instrument. One way that cracks can frequently be identified is that they tend to follow the grain (wood cracks that cross the grain usually come from a severe blow, and this will be obvious). Cracks in the top wood are of particular concern because the top is generally a softer wood than the back and sides, and a crack can interfere with the sound-producing ability of the guitar. The width or length of a wood crack doesn’t affect whether it should be repaired or not, because even a small crack can “run” and get big-ger—get it fixed as soon as possible, because a delay could further compromise the guitar’s condition (more on the repair process in a moment).
A finish crack tends to wander across the grain, and most often is best left alone. A repair of such damage is possible but very time-consuming, which usually makes it cost-prohibitive (it involves repeated applications of a strong solvent and often more lacquer, allowing it to dry for a month or more, then leveling and repolishing).
THE REPAIR PROCESS
Once you’ve determined that there is a crack in the wood, what’s next? Even though some cracks may seem like they’d be easy to fix, only an experienced tech will be able to tell how to best approach a repair. For example, edges that are out of register must be brought back level with each other, which can sometimes be done by simply pushing the pieces back in place. Other times, more force from a clamp or strong magnets is necessary to align the edges. A luthier will often use a caul (made of plastic glass or another flat, smooth material) in conjunction with various clamps to ensure that everything remains in line. Once all the pieces are back in place, glue (typically aliphatic resin glue [Titebond] or hot hide glue) is applied to the now closed crack—often by flexing the wood with gentle pressure from inside and rubbing the glue in from the outside.
If the damage has caused splinters or pieces have broken off, the luthier will have to put them back in their original positions, so it’s important to save all the pieces—no matter how small. Putting those pieces back into place means that repairs will take longer, but the essential repair technique will be the same as described above.
Guitars cracked due to extended exposure to low humidity will have to be aggressively humidified (by placing at least two humidifiers into the case) before taking any of the repair steps above. In my shop, where we maintain a constant 45 percent humidity level, it usually takes about two to three weeks for a crack that’s related to low humidity to close up. Once the crack is closed, it can be repaired like any other crack. Very old or dirty cracks may never fully close up. These may need to be filled with similar wood, and the repair will be especially visible.
CLEATS ON THE INSIDE
The next step will be for the luthier to glue small wooden cleats inside the guitar that span the crack. These cleats are used as reinforcement and are clamped in place—using specialized clamps or, in recent years, extremely strong “rare earth” magnets—while the glue sets for maximum strength. The cleats should cover both ends of the crack to prevent it from getting longer, or “running.”
On curved surfaces that are difficult to cleat, glue-impregnated cloth such as muslin or silk may be used to reinforce the inside of a repaired crack.
Once the crack is glued and cleated the next step is finish touch-up. Generally this will be the most expensive part of the repair because it is very time intensive. Depending on the value of the instrument, this work may not be cost effective. And on vintage instruments, finish repairs may actually diminish the value of the guitar. In any case, it is unlikely that finish repair will significantly improve the structural integrity, the longevity, or the tone of the instrument, so it is important to discuss any questions you have about these issues with your repair person.
The good news is that a properly repaired crack should restore your guitar to full structural integrity and not degrade the tone. This is particularly true of cracks that run with the grain. Severe cross-grain cracks are more problematic, but when a guitar is well repaired and has all braces intact, its tone should not be noticeably impaired.