Forsman Guitars • Article

Humidity and Your Guitar:

A well made wooden stringed instrument, when properly cared for, can be a true joy to look at and play. Unfortunately however, such instruments are all too often not given proper care, and suffer as a result. In this article I will be discussing the importance of maintaining proper humidity for your stringed instrument. I will be focusing specifically on the acoustic guitar; however, humidity management principles apply to all wooden stringed instruments.

To understand the importance of the role of humidity on your instrument, it is important to understand the relationship that wood has with water. Wood is a hygroscopic material, meaning it absorbs and releases water relative to the humidity of its environment. Wood expands as it absorbs water and contracts as it releases water. You will have observed this any time you have witnessed a sheet of copier paper curling under high or low humidity conditions. This hygroscopic property of wood has great implication in the design and care of musical instruments.

The term “relative humidity” (or RH) refers to the amount of moisture in the air at a specific temperature, and can be easily measured using a hygrometer. A quality stringed instrument will be built in a humidity-controlled environment which will generally fall within an RH range of 40-60%. Such instruments should always be stored in this humidity range, and will only play at their best when kept within this range. Brief exposure to humidity outside the optimal range is often unavoidable, and not likely to cause a problem; however, longterm exposure can cause damage that cannot always be reversed simply by returning the instrument to its proper humidity.

As RH increases beyond the optimal range, the wood of your instrument will begin to absorb more moisture, and consequently will expand. At humidity in excess of 50%, the thin wooden sound plates of a guitar will swell and bow outward, thus increasing the gentle structural arch of the guitar. As the arch of the plates increases, the action (the height of the strings above the frets) increases, resulting in a guitar that is more difficult to play. Cosmetically, excess moisture can cause the delicate softwood of the top to swell between the grain lines, resulting in a corrugated appearance that can permanently damage the finish. The hardwoods used on the sides, back and neck will often develop small dimples as the finish sinks into the expanded pores of the wood. At extremely high RH, glue joint failure and damage to the delicate internal bracing structure can occur. It is important to note that even moderately higher-than-normal humidity will contribute to an alteration in tone, volume and projection.

As RH decreases beyond the optimal range, the arched plates of the guitar will flatten and even convex, thus lowering the action and causing the strings to buzz along the fret board as the instrument is played. Additionally, the fret board will shrink, exposing the sharp ends of the frets to your fretting hand. This is a common and uncomfortable symptom in dry winter months. In very dry environments, finish and structural cracks can form. Though cracks in the finish (also known as crazing) can often go unrepaired, structural cracks may require expensive repairs which can also result in the permanent alteration of the sound of the instrument. Even moderately low humidity can also contribute to an alteration in tone and playability.

Generally speaking, stringed instruments are best kept in an environment with an RH of 40-60%, relative to a temperature in the range of 65-80°F. The first step in achieving an optimal environment for your instrument begins by monitoring RH through the use of a hygrometer. Hygrometers are available in a variety of forms from analog to digital, and need not be expensive. Digital hygrometers are a good choice, as they are easy to read and often include a thermometer. The choice of where and how to humidify your instrument is entirely up to you. If space is a consideration, the instrument can be stored in its case with a separately purchased internal humidification system. Many case humidification systems are geared toward adding humidity, though dual systems are now becoming available, and can be quite effective. A quality case will serve to insulate your instrument against brief fluctuations in temperature and humidity, such as when transporting the instrument from one location to another. The disadvantage of case storage is that stored instruments tend to be played less frequently, which decreases the gradual tone improvement benefit of frequent playing.

Another option is to create a humidified instrument room. I store all of my guitars on stands in my workshop, where I maintain an RH of 42-47% at 74°F through the use of a small but efficient humidifier and separate dehumidifier as needed. I would recommend the use of evaporative-type humidifiers over mist-type humidifiers, as mist-type humidifiers are known to produce a white mineral powder that could potentially damage the finish of your instrument (not to mention wreak havoc on any electronics in the room).

Controlling humidity is an essential part of caring for any wooden stringed instrument. With only a small investment of time and money, you can greatly increase the life, value, and enjoyment of your instrument.


Humidity and Your Guitar: A well made wooden stringed instrument, when properly cared for, can be a true joy to look at and play. Unfortunately however, such instruments are all too often not given proper care, and suffer as a result. In this article I will be discussing the importance of maintaining proper humidity for your stringed instrument. I will be focusing specifically on the acoustic guitar; however, humidity management principles apply to all wooden stringed instruments. To understand the importance of the role of humidity on your instrument, it is important to understand the relationship that wood has with water. Wood is a hygroscopic material, meaning it absorbs and releases water relative to the humidity of its environment. Wood expands as it absorbs water and contracts as it releases water. You will have observed this any time you have witnessed a sheet of copier paper curling under high or low humidity conditions. This hygroscopic property of wood has great implication in the design and care of musical instruments. The term “relative humidity” (or RH) refers to the amount of moisture in the air at a specific temperature, and can be easily measured using a hygrometer. A quality stringed instrument will be built in a humidity-controlled environment which will generally fall within an RH range of 40-60%. Such instruments should always be stored in this humidity range, and will only play at their best when kept within this range. Brief exposure to humidity outside the optimal range is often unavoidable, and not likely to cause a problem; however, longterm exposure can cause damage that cannot always be reversed simply by returning the instrument to its proper humidity. As RH increases beyond the optimal range, the wood of your instrument will begin to absorb more moisture, and consequently will expand. At humidity in excess of 50%, the thin wooden sound plates of a guitar will swell and bow outward, thus increasing the gentle structural arch of the guitar. As the arch of the plates increases, the action (the height of the strings above the frets) increases, resulting in a guitar that is more difficult to play. Cosmetically, excess moisture can cause the delicate softwood of the top to swell between the grain lines, resulting in a corrugated appearance that can permanently damage the finish. The hardwoods used on the sides, back and neck will often develop small dimples as the finish sinks into the expanded pores of the wood. At extremely high RH, glue joint failure and damage to the delicate internal bracing structure can occur. It is important to note that even moderately higher-than-normal humidity will contribute to an alteration in tone, volume and projection. As RH decreases beyond the optimal range, the arched plates of the guitar will flatten and even convex, thus lowering the action and causing the strings to buzz along the fret board as the instrument is played. Additionally, the fret board will shrink, exposing the sharp ends of the frets to your fretting hand. This is a common and uncomfortable symptom in dry winter months. In very dry environments, finish and structural cracks can form. Though cracks in the finish (also known as crazing) can often go unrepaired, structural cracks may require expensive repairs which can also result in the permanent alteration of the sound of the instrument. Even moderately low humidity can also contribute to an alteration in tone and playability. Generally speaking, stringed instruments are best kept in an environment with an RH of 40-60%, relative to a temperature in the range of 65-80°F. The first step in achieving an optimal environment for your instrument begins by monitoring RH through the use of a hygrometer. Hygrometers are available in a variety of forms from analog to digital, and need not be expensive. Digital hygrometers are a good choice, as they are easy to read and often include a thermometer. The choice of where and how to humidify your instrument is entirely up to you. If space is a consideration, the instrument can be stored in its case with a separately purchased internal humidification system. Many case humidification systems are geared toward adding humidity, though dual systems are now becoming available, and can be quite effective. A quality case will serve to insulate your instrument against brief fluctuations in temperature and humidity, such as when transporting the instrument from one location to another. The disadvantage of case storage is that stored instruments tend to be played less frequently, which decreases the gradual tone improvement benefit of frequent playing. Another option is to create a humidified instrument room. I store all of my guitars on stands in my workshop, where I maintain an RH of 42-47% at 74°F through the use of a small but efficient humidifier and separate dehumidifier as needed. I would recommend the use of evaporative-type humidifiers over mist-type humidifiers, as mist-type humidifiers are known to produce a white mineral powder that could potentially damage the finish of your instrument (not to mention wreak havoc on any electronics in the room). Controlling humidity is an essential part of caring for any wooden stringed instrument. With only a small investment of time and money, you can greatly increase the life, value, and enjoyment of your instrument.
©2012 Forsman Guitars • Design by Adam Forsman