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Humidity issues – too little or too much – are both insidious (you can’t see it) and pervasive.  Manufacturers warn owners to control the humidity of the guitar’s environment but many players are still either confused or oblivious to the problem. Here are a few thoughts from the perspective of a builder and repair shop.

 A few basics:  The wood in a guitar must be dry or it will be very likely to warp or crack.  As a result manufacturers dry their wood to an “optimum” moisture content of about  6 – 8% and  keep their manufacturing facility at about 45% relative humidity.  Experience has shown that these conditions will result in a guitar that is stable under normal conditions.  However, wood  is still an organic material and susceptible to changes in climactic conditions.  In conditions of low humidity the wood will continue to lose moisture and shrink.  Conversely it will gain moisture when conditions are damp and this will cause it to swell. The consequences can be dire.

  The greatest danger is low humidity.  Any part of the country where there is a heating season (or where there are desert conditions)  is likely to see low humidity.  Here in Minnesota winters will sometimes see humidity in homes go below 10%.  Under these conditions the wood in the guitar will shrink considerably. 

 The principal danger from low humidity is cracks in the top (soft woods like spruce are more prone to humidity problems than hardwoods), though backs and sides will also crack quite easily.  Some guitar woods, such as Brazilian Rosewood, are more susceptible than others. .  Another likely problem is shrunken fingerboards, resulting in frets protruding from the edge of the board.  The most common problem, and in many ways the most aggravating (but ultimately less damaging) , is that the top will flatten out or even go concave, resulting in a lowered action and string buzzing.  In my shop we call this the “salad bowl effect,” and it can often be seen from across the room.  

 So, low humidity can damage your guitar.  How to prevent this?  First, be aware of the humidity level in your home (or wherever you store your guitar).  Humidity gauges can be had from any number or sources, often for $25-50 (look on the internet for sources).  These may not be accurate enough for scientific purposes but for the guitar player they are fine.  The goal is to keep your home/guitar room at about 45% relative humidity.

  If the humidity is too low, what next?  A room or home humidifier is a good idea, but often not enough.  In most winter climates at somewhere about 30% relative humidity the moisture in the air will condense on the (cold) windows and the room will not get more humid.  At that point a guitar/case humidifier is in order.  There are several on the market (see Sidebar).  While I prefer the humidifiers which cover the soundhole and keep the moisture inside the box, the others will do fine if they are kept with the guitar in a closed case and kept damp on a regular basis.  They should be checked every two or three days (you do play your guitar that often, don’t you??). If you want to keep the guitar hanging on a wall, then the humidifiers which cover the soundhole are especially valuable as is a room humidifier.   When filling humidifiers, especially the ones which fit in the soundhole, be careful that they do not drip water into the guitar.  This can lead to unsightly staining and, in some cases, damage to the guitar.  In especially dry conditions (5 – 20%) I recommend two humidifiers be kept in the case.  The traditional “soapdish” unit (see Sidebar) is a good choice to keep in the peghead area of your case.   If your humidity is moderately low (25 -35%) one in-case humidifier will be enough.  Don’t over humidify – if the room humidity is 40% or more, you can stop using the humidifier.  If your guitar is over humid, the main symptom will be loss of tone and volume due to the swelling of the wood.   If you do all of the above diligently, your guitar should be safe. 

 Often we will get a customer who says “I have had my guitar for 20 years and never humidified it, and in all that time I have had no problem.”  Often they tell me this while I am explaining why their guitar has developed a major crack in the top.  The answer is that no guitar is “safe” without proper care and the fact that it has survived this long is only proof of the following maxim:  “It has been exhaustively demonstrated that under rigorously controlled conditions carefully selected pieces of wood will do pretty much what they damn well please.” 

 What if you are in a dry area for only a day or two?  You are probably safe but remember the maxim above.  If you own a humidifier, use it, even if only for a short period.  Better safe than sorry. 

 Do you live in an area with abnormally high humidity conditions?  Then you have a whole different set of problems, and that is a discussion for another time. 


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2219 East Franklin Ave.
Minneapolis, MN. 55404  or

(612) 338-1079