I hope you have many, many years of pleasure playing your guitar. The best way for you to be able to protect your guitar from damage is to understand what factors affect it and how best to control these factors.
Temperature and Humidity
The most important factor in protecting a solid wood acoustic guitar is to understand the effect of temperature and humidity on it.
Many of us who grew up in dry, cold climates believed that dry, cracking lips in the winter were just a part of life. In general, the conditions which humans find most comfortable are the best for a solid wood instrument. Having realized this then, instead of defining a humidification regiment that could never properly address all situations, I recommend that you buy a digital hygrometer and sensitize yourself to the conditions required to protect your acoustic guitar. Once you have purchased a hygrometer it is imperative to understand what you are measuring.
A hygrometer measures the amount of Relative Humidity, or RH, in the air. RH is the amount of moisture in the air relative to the amount of moisture the air can hold before it reaches the saturation point. As the temperature of the air rises, so does its ability to hold additional water.
In the winter when people are artificially heating their homes and studios, three things happen:
- As the temperature increases without an additional source of moisture in the house the RH drops.
- The air you are starting with before you heat it is very cold, meaning that it is carrying very little moisture even when the RH is very high, such as in a snowstorm. Because cold air has a very low saturation level, it will carry very little moisture. Even if the RH is high when it is cold, by the time that air is warmed up to 75 degrees, the RH will be extremely low. The saturation point of air at higher temperatures is so much higher, that the RH will be very low, unless significant moisture is added to that air.
- The actual mechanics of heating, especially when using wood or electric methods of heating further dries out the air. The result is that if you live in a dry area, such as the notorious Rocky Mountains, or in any area when it gets very cold, you will have to be careful to protect your guitar from low humidity damage.
Dealing With Low Humidity Conditions
If you generally keep your guitar inside your house and prefer to keep it out of the case, you should have a room humidified to 40% to 45%, and a hygrometer monitoring the RH of the room. Many reasonable room humidifiers are available from between $50 to $200 and remember it will make you and your family more comfortable too.
If you don't have a humidified room, or are traveling or gigging a lot, you will need to humidify and monitor the RH of the guitar in the case. The case insulates a guitar from rapid changes in humidity and temperature and from physical damage anyway, so even in a humidified room, it is best to have the guitar in the case whenever possible.
Install the hygrometer on the body side, outside of the accessory compartment of your case. Then humidify by placing the humidifier in the accessory compartment. This way the hygrometer will only read what moisture is available to the instrument not what is coming out of the humidifier. There are many good brands available, but keep in mind we don't recommend putting any of them in the guitar. Put the humidifiers in the accessory compartment and use 2, if necessary, to get the reading up on the hygrometer, which should be right next to the heel of the neck on the guitar. This way there can be no chance of leaking which will destroy the instrument. If you can't get the reading up, having the humidifiers in the accessory compartment, try putting one in under the headstock.
Low Humidity, below about 40%, can cause cracking in both the wood and lacquer. The top will drop, lowering action to the degree that the strings will buzz, sometimes to the degree that it becomes unplayable. Lacquer checks will develop along the purflings, bindings, and at glue seams. The fingerboard will shrink, leaving the fret ends protruding beyond the edge of the binding and feeling sharp. This makes the instrument uncomfortable to play. Usually the first symptom to develop will be a slight dropping of the top and lower action, followed by the possibility that a hairline crack may develop along the bridge pin holes. This is an excellent early warning symptom. It is easy to fix and it lets you know that you are headed for trouble if the humidity problems continue.
High Humidity Conditions
If your problem is high humidity, it will be harder to deal with, but it is also is a safer condition. Air conditioning will really help you keep the humidity at a reasonable level. As the temperature lowers, so does the saturation point of the air, water will condense, and the RH will decrease. High humidity, 65% and above, causes the top to rise, making action high or unplayable. It can cause lacquer to check, impressions of the braces may appear on the top and puckers may appear where the top is glued to the internal structure of the guitar, such as at bridges, braces, head blocks, and tail blocks. It also restricts movement of the top resulting in a guitar that may sound tight or restricted.
Avoid Rapid Changes
Rapidly changing humidity is the most damaging condition you can expose your guitar to. Having a guitar go from an environment of 85% humidity to 35% immediately could easily cause severe damage to an instrument. If the same instrument were kept in its case, moved into a drier but humidified environment of say 65% for 2weeks then 45% for a few weeks and finally 35%, any damage sustained would likely be far less severe. Your guitar's case is your best tool for insulating your guitar from extreme conditions and rapid changes in conditions. Keep it in its case whenever possible.
The most critical time for an acoustic guitar in terms of humidity is the first 3-5 years. If it has been well controlled and stabilized during that time then it is far less likely to ever have problems. This is why most vintage instruments are less likely to respond to humidity changes than a new guitar would be. This does not mean that the guitar will not move or respond to humidity, but it does mean that you have the best chance possible of keeping your guitar safe by understanding and responding to the factors affecting it.
Once a guitar has been dried out, the humidity needs to be restored. To do this often humidifiers must be put into the guitar such as a Dampit and the sound hole sealed off. Be very careful in doing this. All of the excess moisture must be wrung out and the guitar should be put in the case for about 3 days and then rechecked. It will help to also have a humidifier under the headstock to make moisture available to the bridge and fingerboard. They should also be oiled. Expect this to take about 2 weeks before the action is restored and the guitar can be assumed to be re-humidified.
You may find that not all of the symptoms are completely resolved. Some problems such as sharp fret ends may need further professional attention, but this is a relatively inexpensive procedure that can be done by any competent repairman.
High temperatures, generally above 100 degrees, cause glue joint failure and softening of the lacquer, making it susceptible to damage. Never leave your guitar in a closed automobile or trunk in hot, sunny weather. The inside of the car can easily go above 100 degrees.
Low temperatures, generally below freezing, cause lacquer to craze and check. One very important point to remember, rapid changes cause far worse damage than the exposure to extremes if the changes take place slowly, with the instrument having plenty of time to acclimate. When, for instance, an instrument has been transported or shipped in the winter, it may well have been exposed to extreme cold. It is best to wait overnight before opening the box or guitar case. I have seen guitars arrive at a destination, get checked for damage, find none, and then the next day found the lacquer checked and crazed. In these cases the guitar was very cold to the touch when examined. This wouldn't have happened if the instrument hadn't been subjected to thermal shock. If it had been left insulated in its case and the box for at least 12 hours, it could have been opened without damage resulting.
When changing strings, lightly clean and oil the fingerboard with lemon oil. If “gunk” has built up around the frets, use a soft toothbrush with lemon oil to scrub it off, and then wipe the fretboard clean.
My guitars are initially set up with D’Addario light strings (.012-.053). If you change the type of strings, it is likely that the action of the strings will change a bit too. Heavier strings will cause higher action, lighter, lower action. So to achieve the action you like, a slight adjustment of the truss rod may be needed if you change the heaviness of strings. When re-stringing your guitar you want only 3 to 4 wraps around the tuning posts. Too many or too few wraps can cause tuning problems. A good way to gauge how much string to wrap is to measure about 1 ½ tuning keys beyond the one you are stringing up. Turn the tuning key counter-clockwise to wind the sting onto the post.
Truss Rod Adjustments
Truss rod adjustments may be made to correct buzzing or lower the action of the strings. Over time, particularly for new guitars, the neck wood settles-in due to the tension of the strings, which approach 180 pounds of pull. Changes in humidity can also affect the height or action of the strings. The truss rod in your guitar is a two-way truss rod. Access to the truss rod is under the small ebony cover on the headstock just behind the nut. A 1/8th inch Allen wrench is provided to make adjustments. Remember, as you look down the neck from the headstock, turning the nut to the left will loosen the truss rod, giving more relief or bowing of the neck (concave shape). This can reduce buzzing by raising the action of the strings. Turning the nut to the right will create back bow, straightening the neck and thereby lowering the action. A properly adjusted neck should have a slight amount of relief. It is important to loosen the strings when making truss rod adjustments. Only very slight adjustments should be made. A quarter of a turn of the nut should produce noticeable change. Too much adjustment can strip the truss rod itself rendering it useless. If you’re not familiar with this adjustment, I strongly suggest having a professional do this as significant damage can occur if not done properly. Most music/guitar stores have a qualified repairman on staff.
Cleaning Your Guitar
Clean the body of the guitar with any good guitar cleaner/polish. Use a soft, clean cloth to apply the polish and buff it off when the polish glazes over/dries.
Occasionally check the screws and nuts on the tuning keys to keep them tight for best performance.
Tips for Travel and Shipping
When shipping the guitar, be sure to pack crumpled newspaper, cloth or bubble wrap around the headstock to give it good support. Where the neck meets the headstock is the weakest part of the guitar, and a sudden, sharp shock can crack or even break the neck at that point.
Never ship a guitar in a gig bag, only use hard cases that will protect the instrument from the abuse of shipping or baggage handlers.