This guest article from Brian Kelleher of KillerGuitarRigs.com will walk you through the importance of controlling the humidity in the air your guitar is exposed to. You’ll also find some helpful methods that every guitarist (and luthier) should be aware of.
In some ways, wood never completely stops being a tree. It continues to strive for moisture equilibrium. A process where it takes in and loses moisture to balance with the environment that surrounds it. This characteristic is what we call hygroscopic.
If the wood is exposed to damp air, it will literally absorb the moisture and hold it. When the environment is drier than the wood’s moisture level, it will release that moisture. Thereby, wood is dimensionally unstable – it will react to an uncontrolled environment and climate conditions such as moisture and temperature (heat/cold).
This is why guitar manufacturers and luthiers work in a controlled environment. They need to control the moisture content of the building environment and the storage area. It warrants painstaking measures to maintain a relative humidity of 45 to 50% relative humidity (RH) at 20 degrees to prevent the wood from shrinking or expanding.
As a luthier, I’ve seen one ‘wet’ guitar too many, all because people ignore the manufacturer’s recommendations. In this post, I’ll throw light on the relationship between wood and humidity.
We’ll also discuss some easy to follow solutions to safeguard your guitar from damage and wear.
Guitar Wood: Changes and movement caused by moisture
From the boot of your car to an overhead compartment to a hotel room, a guitar makes several pit stops in its journey from your storage closet to the stage. Dryness will make the guitar wood crack and moisture will make it swell and/or distort.
There are two primary ways in which wood absorbs moisture: a) when it comes in direct contact with any liquid, and b) from the air. Thus, the guitar wood’s moisture content varies as per the humidity and temperature of the surrounding air.
When you live in a high-humidity area or tropical weather, there is no safe place to store your guitar. You heard that right. Your soft case and closet won’t safeguard it from 70 to 80% humidity. The ensuing damage and repairs, if possible at all, won’t be cheap either.
Moisture, in a nutshell, is the arch-nemesis of wood – the prime suspect for the undoing of any guitar. Acoustic guitars are decidedly more susceptible to damage from changes in moisture content. Either way, the humidity will oxidize the metal hardware components on any acoustic, electric, hollow, and semi-hollow body guitars.
Effect of moisture on the Guitar
It takes a few weeks for the guitar to get affected when exposed to severe humidity. In the case of moderate levels of humidity – 60% to 70%), the over-humidification will happen after a few months of exposure.
Some wood species are more hygroscopic than others and the expansion and contraction are more pronounced. In general, softwoods are less likely to shrink or swell with changes in moisture levels as compared to hardwoods. This is due to their inherent dimensional stability.
The moisture content of wood also affects its mechanical characteristics and alters the acoustic vibration. High moisture content reduces the dynamic elastic modulus of the wood and increases its loss tangent. In simple words, it causes internal stresses that result in volume change and instability in the guitar’s sound.
Telltale Signs of a ‘Wet Guitar’:
In luthier parlance, we use the term wet guitar for any over-humidified guitar. A visual sighting of the neck angle, top/back, and bridge angle are enough to diagnose the problem. On occasion, I will use a straightedge to check over humidification.
The most visible moisture-based damage to a guitar is seen in the top and back. They tend to have a pronounced arch. However, don’t confuse this with acoustic guitars (like the Taylor Big Baby) that have it by design. Here is a quick summary of the telltale signs of a ‘wet guitar’ –
- Cracks in the finish
- High guitar string action
- Fret ends and nut may shrink
- Crack joints swell up
- Glue joints will fail
- Neck angle will get distorted (neck warp)
- “Rising tongue”
- Dull tone and diminished projection of sound
- A low spot where the end block is glued
However, guitar players should not try to diagnose this problem unless they know what they are doing. And, I emphatically advise against self-repairs or YouTube remedies if your guitar is already damaged. Don’t make a bad thing worse and let a professional look at it.
How to ensure humidity doesn’t damage your guitar?
Very short exposure to humid conditions (or extremely dry climate) is fine as long as the guitar is immediately stored in a hard shell case after use. Soft cases and poor quality gig bags will not suffice. Continuous exposure can take 5 to 7 days to show on the guitar.
The guitar finish, to some extent, helps deter and reduce moisture absorption i.e. the amount of moisture that can enter or leave the wood. Despite that, your guitar isn’t impervious to moisture.
All guitar manufacturers recommend an ideal humidity, usually between 45 to 55 percent humidity. However, it is unrealistic, if not impossible, for guitar players to maintain that humidity level for a room or home – unless they are willing to go to great lengths to achieve it.
There is a simpler way to do this. Create a micro-climate in the guitar case. Get a guitar humidifier that works and keep the guitar at RH levels. Here are some important tips to protect your instrument:
Don’t leave your guitar in any dark, warm or moist area. For instance, don’t leave a guitar by the window or in the boot of your car for any longer than required. Secondly, keep your instrument at a safe distance from radiators or underfloor heating.
Don’t expose the guitar to a sudden change in humidity i.e. from a dry to a very humid environment. A guitar will gradually acclimate if kept inside the case for 36 to 48 hours. Humidity and temperature are not mutually exclusive.
Additionally, humidity varies as per the season and your lifestyle (heaters, air conditioners, etc.). Central heating accounts for a cold but dry environment in winter. Invest in a good hard case. It is the only real protection against temperature and humidity changes.
Desiccants refers to any hygroscopic substance (solids that absorb water) that are used to create a state of dryness. The most common pre-packaged desiccants are silica gel packets that are shipped with a guitar (and other items like shoes, vitamins, supplements, etc.
Desiccants induce dryness and create a moisture-free environment over time. They should not be permanently stored in your guitar case as they will dry out the wood over time. This is not healthy for the guitar as it will lead to cracks and waves in the finish. Only use a desiccant when your guitar or guitar case gets wet.
Monitoring & Adjusting Air Humidity
> Monitor: Digital Hygrometer
A hygrometer is a device that gauges the humidity levels and provides an accurate reading. A digital hygrometer is advised to check the humidity your guitar receives. It has an LCD that shows humidity and temperature simultaneously.
You can buy an analog hygrometer but they are notorious for bad readings. They can fall out of calibration, show fluctuating readings over time, or the needle can get stuck. You can buy a good digital hygrometer at your local music stores or via online retailers. Here are my top three recommendations:
> Adjust: Humidifier
Once you check the moisture level with your hygrometer, you will to either deal with dry or wet guitars. If your guitar is dry you have to re-moisten it. To do this, you have two options: a) refillable humidifiers and b) use and throw packs.
You can easily find a good guitar humidifier at your local store or on Amazon and other online platforms. Nevertheless, here are my top three recommendations:
Refillable humidifiers will save you money in the long run. You need to buy them once and then pour in clean water to refill them once they dry out. That’s a little more effort for saving money but it comes with the danger of over-humidification if you recharge it before it dries out.
As mentioned earlier, the Relative Humidity (RH) for a guitar is 45-55%. If the guitar is dry (below 40%), you need to re-moisten it. You can store a humidipak or humidifier inside the guitar case. The ideal spot would be somewhere in the center, facing the neck joint. Don’t forget to use Velcro to keep the humidipak in place.
D’Addario’s two-way system is ideal for the optimal 45-50% RH level in an instrument case. It reduces and adds moisture without putting you through any calculations or conjecture. In other words, it is a ‘set-n-forget’ system that lasts 3 to 6 months. Once the pack becomes firm, discard it and replace it with another one.
If you own a premium guitar with high-quality tonewoods (or are in the mood to splurge), I highly recommend the D’Addario Planet Waves Humiditrak. It is a device that can be placed in your guitar case that will monitor the humidity levels and instantly notify you via Bluetooth when it needs attention.
An expensive guitar needs proper care – not because you paid a lot for it, but because it is a lifelong companion. However, there no need to walk on eggshells. You can reverse the movements in your guitar that have been exposed to 60%+ RH levels.
Just follow the simple tips and methods I’ve outlined and your instrument will dodge any long or short-term damage that humidity levels pose.