Acoustic guitars are constructed from woods that are specifically singled out because of their exceptional tonal qualities, and also because they are aesthetically pleasing.

The tops of acoustics are typically made out of spruce, and sometimes from cedar. Pines are very soft, and because of their fiber structure, are excellent for creating resonance and volume for the guitar. This is probably the most important piece of wood on the guitar, for a few reasons.

  1. Bracings

    The bracings on the inside of the guitar are glued to the top. These bracings are created in a pattern that is meant to maximize the resonant frequencies of the instrument -- each manufacturer has a different methodology for the construction of these bracings, but they all use them.

  2. Resonant Frequencies

    Over time, the pine fibers loosen up. This allows the guitar to gain volume, and also helps with the harmonic qualities between notes because the wood absorbs the frequencies that are applied to the instrument. This actually makes the tone sweeter -- the resonant frequency pattern of the instrument will change over time to focus on the notes that are played. This is a point of great interest for instrument-makers, particularly strings. Perhaps the greatest example of this is the Stradivarius violin. What makes these instruments so valuable is that the resonant pattern is so closely ideal to that of the instrument.

  3. The Finish (Varnish)

    Although the whole guitar is finished (usually), the finish on the top of the guitar is special. If you do not keep the guitar properly humidified, the finish can have a few terrible things happen to it. Modern UV-cured finishes are more resilient to the effects of humidity, but the fact remains that other parts of your guitar will be negatively affected by adverse humidity conditions, such as the neck and the back.


    Rapid temperature changes applied to the finish will typically result in something called cold-checking where the finish cannot withstand the temperature difference. Polymers typically become brittle at colder temperatures because they take on a more rigid structure -- a change to the temperature can disrupt the weaker bonds in the structure and cause it to fracture the chains.



    You will know that your guitar is absorbing too much water when

    • The frets have sunken into the neck a bit, because the neck wood is swollen. This is much more difficult to notice than if they are sticking out, but just take a close look.

    • The action is getting really high, but you have done the proper truss rod adjustment to assure that the neck is straight.

    • You notice a lump behind the bridge, or that there is a gap between the bottom of the bridge (away from the neck) and the body of the guitar.

    • The back of the body is bowing outwards more than the manufacturer intended. Some guitars, like my 2002 Taylor 414CE, have some natural bow to the back, so that if you were looking across the back at a straight angle, you would not be able to see the other edge. However, it should only be about 1/2" of a rise across the back.

    • When you play above the 9th or 10th fret, you get a lot of buzz. That's because the top is bloating outwards like a balloon, and the part of the neck attached to the body is getting pushed up. Combined with the slight natural curvature of the neck, the strings will not have a clear path back to the bridge.

    Over time, an acoustic guitar that is in too humid of an environment will soak up the humidity into the wood. The wood will naturally expand, and the bracings will no longer keep the shape they were designed to. This can cause humps in the top of the guitar, and possibly other spots of high tension where the finish will not be able to withstand the physical shape it has been placed in, and will consequently crack. If you live in a locale that regularly has a relative humidity (RH) of above 60%, you should take steps to prevent this from happening to your instrument. If you have central air, don't fret about it too much, but even so, you may want to pick up some silica gel packets to put in your case when the instrument is not in use to soak up the extra humidity.

    TOO DRY:


    You will know that your guitar is not absorbing enough water when:

    • The frets are sticking out on the sides of the neck, and you are bleeding all over from being sliced.

    • There is a gap between the piece of the neck sticking over the body and the top of the body. This is caused because the wood is shrinking, and the top is beginning to sink in.

    • The action is way too low, and it is buzzing all over the place even if you are pressing really hard, and regardless of where you are playing. Once again, the neck may be straight (or slightly bent, as it should be) but the body is sinking in and the bridge no longer lines up properly with the end of the neck that extends over the body.

    • Your guitar is screaming at you for water. By now, it may already be too late. You paid a lot of money for the thing, you need to nurture it!

    This case is very similar to the too-humid condition in the effects it can have on the wood. In extreme cases even the wood itself may crack, or the joints of the instrument can come unglued, which could be very difficult or expensive to fix.

In order to prevent these horrific tragedies, there are some readily-available instruments that can aid you in your quest for happy guitars. Go to Radio Shack and pick up a hygrometer. This device will enable you to know what the RH is in the air around your guitars. Keep this meter in your case, and monitor it regularly to see what kind of environment your instrument is being subjected to. Once you have determined that you have a problem, you can start to solve it. In the case that you have too much wetness, use the advice above and get some silica gel packets to leave in the case. You can also use a hair blow-dryer on THE CASE WITHOUT THE GUITAR IN IT. Do NOT blow-dry your guitar, no matter what "respected" source told you otherwise.

For the too-dry problem, you are going to have to purchase a humidifier. They are about 10-15$ from a guitar store.


Once you have purchased the humidifier, you may not realize that only a little bit of moisture can go a long way inside the instrument. Having outright drops of water inside of it can cause the wood to ROT THROUGH. When you get the sponge wet inside the humidifer, SQUEEZE IT OUT THOROUGLY UNTIL NO MORE DROPS ARE COMING OUT.

It may take some time to get just the right amount of water, but you will get the hang of it. If the sponge dries out in two or three days, you are probably not adding enough, or the instrument was really starved for water. You should leave the humidifer inside the instrument when it is inside its case, having it in while the instrument is out is pointless, as the room will soak the water right out of the sponge.


After you've been using your humidifer for a while, and you're feeling great, you may notice that your guitar is starting to not play very well, and you feel like you really suck and your guitar sucks too. At this point, as yourself: did I just over-humidify this instrument? It is easy to do. Buy a hygrometer and monitor your progress. Don't over-do it because this could be just as costly as letting it dry out.


When you are playing your guitar, you may notice that some areas of the neck make your instrument buzz at you. In the instance that this involves playing an F barre chord, you may just not be pressing down hard enough. However, if this occurs spottily in different areas of the neck, you are probably going to have to either do a truss rod adjustment, or get your frets dressed/replaced. Truss rod adjustments are covered in another node. Most importantly make sure the strings are tuned up to concert pitch for a guitar, that's EADGBE, when you do the adjustment.

The frets will wear on their own, they are tempered and they are steel (probably), but over time they will get divots from you pressing the strings onto them and wiggling your little digits around. Even if you notice considerable divots, you may not have to get the frets completely replaced. Dressing the frets can done in this case, where you take a file and level off the frets. During this process you are removing a consderable amount of the metal, so you can probably only dress the frets 3 or 4 times before they must be replaced.

Dressing process:

  • Using a smooth mill file, work across the tops of the frets, pushing towards the headstock. Lay the file across as many frets as it can reach at one time, and press very gently since you want to remove only as much metal as you need to, no more.

  • Once the divots are no longer visible and you have only removed a SMALL amount of metal from each fret, grab your favorite 200- and 400-grit sandpaper successively, and work across the frets IN THE DIRECTION OF THE GRAIN OF THE NECK -- again, this is cross-wise to the frets.

  • The last step, 000 steel wool, is where you will actually work length-wise across the frets to smooth them out in the end. This will remove burrs, and the straight edges that have been left over. Different shape frets are used by different companies, so filing them will be different depending on if they are very flat to begin with, or tapered in a hemisphere shape.

Dressing your frets is something that you should take pretty seriously, and if you don't think you can do it properly don't hesitate to take it to a luthier. However, make sure that the luthier you are taking it to is someone who you have good recommendations about, because you don't want to just leave your nice, untainted guitar with some asshole who will mess it up and then charge you out the wazoo.

Extended Instrument Storage

In the instance that your instrument will remain unusued for a long period of time, say a month or two, then you will need to take a few steps to assure that it is in the same condition when you open the case back up as when you put it in.

  • You can store the instrument with the humidifier in it -- many humidifiers come with a dome that can cover the soundhole to keep the moisture in, so you will not need to replenish the sponge.

  • Keeping the truss rod under full tension for a long time if the instrument is not going to be played could be potentially harmful. This may seem counter-intuitive, since truss rods should only be adjusted when the strings are under 100% tension. However, because the humidity and tension on various parts of the guitar can be different in different areas of the case, loosening the strings for extended storage is advisable. This will prevent the neck from warping, or nasty things happening to the headstock or the joint where the neck meets the body. Probably only 3/4 of a turn on a 14:1 tuning peg will be enough of a release to help the instrument.

    A brief explanation of tuning peg ratios: the higher the ratio, the more turns it will require to equal one turn of the string-hole part of the peg. As in, you turn the key 14 times, the little hole will have just made one complete revolution. What a pain in the ass, you say? Get a string winder and shush.

Instrument Shipping

When you are moving, or potentially sending in your guitar for repair, you should take a few steps to assure that it is not damaged in transit. Loosening the strings a little bit will help -- imagine the UPS guy actually caring which side is "up" and just dropping it over so that the strings pulling on the neck happen to be helped out considerably by angular momentum and a sudden burst of kinetic energy... it's not pretty, and on many guitars the headstock is the weakest point.

Additionally, REMOVE THE BATTERY if your guitar has a built-in preamp. Imagine that little sucker flying around in there banging into the unfinished insides. This kind of damage will surely make your instrument despise you, and may make it sound like crap.

Thanks to grwghow and Devon for their excellent suggestions on how to improve this write-up!