Guitar maintenance: humidity

Strings attached

Now that you’ve invested in a guitar from Spain, we want to ensure that your instrument produces the same beautiful sound it does today for many more years to come. Or a more beautiful sound, the longer you play it. And not just because you’ve been practising.

As you know, your classical or flamenco model was made from several different tonewoods. Each of these was chosen for its particular acoustic properties, such as the ability to transmit sound without distortion. The woods were first carefully selected by a skilled guitar maker and left to age in climate-controlled conditions for some time – in some models, decades – before the wood finally reached the necessary stability for the luthier to assemble the pieces.

The Raimundo 105M Classical guitar has a cedar top, which, as well as spruce, amplifies sound to perfection

In season

For structural reasons, wood needs to be patiently seasoned before it can be used to build a quality instrument, because in its natural ‘green’ state, it is saturated: it can literally have a water content of 100%. And even when a tree is felled and cut into thin pieces of timber, it can still absorb water. This is why luthiers carefully choose the wood years before they intend to use it: the longer they store it in stable drying conditions where it slowly shrinks and swells to attain equilibrium, the better the final instrument will withstand changes to humidity in the environment.

The tonewoods of the Raimundo 185 Gomalaca Classical Guitar are allowed to mature for years. A handmade varnish applied to the soundboard completes the meticulous process

Good atmosphere

Having said that, because of the delicate construction of acoustic guitars, even the most seasoned wood is susceptible to humidity in the atmosphere. And the smallest change can have an impact on the sound and playability of the instrument. The most stable environment is, of course, a good guitar case, so if the humidity levels in your house are not ideal, simply keeping it there when you’re not playing it will help you avoid most problems – as well as unwanted knocks.

The uber-stylish, light and protective Alhambra 9558 Carbon fiber guitar case

But you didn’t buy your instrument to keep it locked up all the time, and an exposure to dry or humid surroundings is generally okay if it’s only for a few days (unless your instrument is a rare and valuable collector’s item). If humidity levels are suitable, it’s actually a good idea to bring your guitar out to air. Just don’t keep it anywhere near radiators or underfloor heating when you do, as these can cause damage.

In hot water

A ‘wet guitar’ is how guitar repair technicians refer to an instrument that is showing signs of excess moisture. This can happen when it has been exposed to humidity above 60% for more than a few days, and has literally begun taking on water.

This is because wood is hydroscopic – which in plain English simply means it easily absorbs or expels water until it is in moisture equilibrium with its surroundings. Any excess moisture in the air will cause the wood to expand and swell, which will result in the pieces separating where they join – for example on the bridge. If this happens, it will affect the action and playability of the instrument.

The most common symptom of a wet guitar is high action – sometimes to the point where your guitar becomes too difficult or painful to play. If you have a good ear, you might also notice that your instrument has started to lack resonance or sounds dull.

Home and dry

Dryness however, can actually be more of a problem for your guitar than excess humidity. When the wood is dehydrated, cracks can start to appear on the soundboard. Warping of the neck can also occur and this results in lower action and an unwanted buzzing sound when the strings come into contact with the frets.

The width of the fingerboard can also shrink to the extent that the frets stick out beyond the edge of the neck, the back starts to look flat and the soundboard sunken. All of these, as well as loose machine heads and bindings cause significant performance issues.

The Camps M-1 Classical Guitar with zizicote back and sides and mahogany bindings

Within range

So, what do we consider acceptable levels of humidity? Well, the ideal relative range is 45-55%, but it’s not until you’ve left your guitar in an extreme environment for about a week that you may start to see the first signs and symptoms of a wet or dry guitar.

It’s also important to avoid any sudden fluctuations in humidity. If you live for most of the year in a dry climate, and go on holiday to a somewhere in a humid climate zone, keep your guitar inside its case for a couple of days, to let it slowly become acclimatized.

And don’t forget that humidity levels change between one season and another: in winter our homes can get very dry due to central heating, and in some places, summer can get very humid. 

Likewise, if you’ve been transporting your guitar in your car (preferably not in the trunk, btw), bring it inside the house straight away when you get home, but don’t remove it from the case until it reaches room temperature: exposing it to a cooler or warmer room too quickly can cause damage to your precious instrument.

The luxe Cibeles C200.008FG-AM Classical Guitar case comes with a hygrometer

Not high maintenance

Thankfully, you don’t need to be a meteorologist – or spend a fortune – to weatherproof your instrument and keep it safe from too little or too much water vapor in the air.

You can purchase a hygrometer for your guitar case to monitor relative humidity and make adjustments as necessary: you can also install a guitar humidifier inside the sound hole of your instrument, which is especially important in the winter months if your heating system is circulating warm, dry air.

And if you are lucky enough to live in a tropical part of the world, where it’s humid all year round, you will need to use a dehumidifier in the room where you keep your guitar. They come in all sizes and some are even portable. You can also purchase little desiccant pouches that fit in your guitar case to absorb excess moisture: just remember to replace them when they become saturated.

The lates humidity control devices for your instrument works both ways, adding or subtracting moisture according to the need of the instrument. One example of these devices is the Boveda.

On a final note

One last piece of advice for any performers out there: when you leave the concert hall, theatre, or venue at the end of the evening, don’t drive away with your instrument on the roof of your car. We only feel we ought to mention this unlikely scenario, because it is just what happened to GFS’s founder way back in the 1980s as a young cantautor in Jerez de la Frontera. In this event, it really won’t matter if it’s cloudy or bright. Your precious instrument will be blowing in the wind.