Humidity and Your Guitar

Wood is amazing stuff.  Simply put, a tree is has three main parts; the roots, the leaves and the stuff in between we call wood.  From the tree’s perspective, wood is little more than a plumbing system used to convey water from the roots to the leaves and back again.   On the cellular level, think of it as a bundle of pipe.  What does this have to do with a guitar?  Everything!  It is this structure that makes wood so strong in certain orientations and allows it to freely resonate.  Luthiers take great pains to use the right piece of wood, from the right tree, cut in the right way and seasoned in the right way.  Why?  Believe it or not, it has little to do with looks; it’s all about strength and stability.  Wood shrinks and swells quite a bit in response to humidity changes in spite of the pains we take.  There's the rub, wood never looses its affinity for water and humidity is water.

 Humidity comes in two varieties, absolute and relative.  Under normal circumstances, (anything short of getting caught in the rain) your guitar is concerned with Relative Humidity, (RH).  Relative Humidity is relative to temperature and warm air can hold more water than cold air.  It's these two facts that cause our problem.  If you were to take a fixed amount of air, seal it in a box with a hygrometer, (a device used to measure RH expressed as a percentage of the maximum amount of water the air can hold before it precipitates) then cooled the box, the RH reading would rise.  If you cool it enough, the water will condense and precipitate out of the air.  This is how clouds and rain work.  Conversely, if you warmed the box, the RH reading would drop.  This is what happens when we heat our homes.  Understanding this, luthiers build guitars in humidity controlled environments, usually maintaining a happy medium of 45% RH to allow for the greatest “safe range” in either direction.  The "safe range" is generally thought to be between 30% RH and 60% RH though I would avoid the edges of this.   Outside of this range you will encounter problems.

 I live, build and repair in Calgary, Alberta, on the lee of the Rocky Mountains.  The land here is a high, sometimes very cold, desert.  We gratefully receive frequent breaks from the cold in the form of Chinooks; a warm, very dry wind that blows down the lee of the mountains as a result of compression in the upper atmosphere.  So, this little treatise will focus on the effects of low humidity rather than high humidity.  High humidity can swell wood severely, induce rot and cause glue joints to fail.  Low humidity can cause wood to shrink, crack, and permanently alter its shape which can lead to all sorts off trouble for a guitar.  Neither of these scenarios are very pretty.  These effects can be compounded by the rate at which the RH changes.  If this rate exceeds the woods capacity to absorb the change, bad things can happen very quickly.  So what does all this mean to your guitar?

 A guitar is a precisely engineered machine made from wood.  The better the guitar, the more precise this engineering is.  In an effort to make the guitar louder, more responsive and more complex in tone, we take this engineering closer and closer to the edge of structural stability.  This is what the player wants; unfortunately, this comes with a greater responsibility to the guitar as the effects of low humidity and rapid changes in humidity are magnified as the structure is made lighter.  So what do we do?
 

• Prevention:  As with us humans, prevention is always preferable to treatment.
  • Buy a hygrometer and use it both in your case and in your home to monitor the RH.
  • Prepare your home by humidifying it.  Most of us have a humidifier on our furnaces, but few of them work well and they only work when the furnace is running.  A stand alone humidifier, placed in the room were the guitar is stored is best.
  • Keep the guitar away from heat sources such as air vents, sunny windows and in-floor or radiant heaters.
  • Use a small humidifier in the guitar case at home if the house is not controlled and certainly on the road.  Check it often.
  • Buy a laminate wood campfire guitar for the outdoors lest you be tempted.

                                                                                                                                  The Top has Collapsed

• Signs Your Guitar is Dry:  Some of these are obvious, others more subtle.  The key lies in knowing your guitar so you can notice the changes.
  • Changes in action and playability.
  • Poor tone or lack of volume.
  • Cracks and dips in the wood.
  • Fret ends becoming sharp and sticking out past the edge of the neck.
  • Separations at glue joints, a curling rosette or bridge.
  • A crack running between the bridge pins.
  • A gap forming between the guitar top and the bottom of the bridge.
  • The end of the fingerboard bending down towards the soundhole.
  • Cracks in the fingerboard, especially in ebony.
  • Internal rattles and buzzes.
  • Loose tuners and bolts.  Many guitars, including mine, are now built with bolt-on necks.
  • The bracing becoming noticeable on the top or back.
  • Changes in the doming or arch of either the top or back.
  • Damage to the finish.
  • A complete collapse of the top or back below the level of the sides.
  • The bridge tears off or the neck joint fails.

• Treatment:  I am able to repair many of the problems created by dryness but not all and not every time.  Wood is funny stuff.  Sometimes little can be done to restore the instrument to its former geometry.  As such, they never quite sound the same and are even more subject to problems in the future.  A great deal of the repair work I do around here is a result of dryness.  If I had a dollar for every...  hang on, I do.
  • It's money you do not need to spend.

One final thought:  I know some of you are thinking "I've never humidified my guitar and it's just fine" or "I've dried it out slowly so it's just fine" or any of the other "explanations" I've received.  There are guitars that seek to prove the adage that wood will do as it pleases; sometimes in your favour.  Consider yourself lucky if it is fine; it may just be, but it's more likely you're just used to it.

                                                                                                                                                         Kevin Turner  © 2007