Acoustic Instruments and Winter Care

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Scott Zimmerman, Master Luthier now residing in Matsumoto, Nagano, Japan.  The mandolin is a Fern model by Mr. Eiichi Sumi.

by Scott Zimmerman

This article originally appeared in a shorter version in Japanese in the Bluegrass journal "MOONSHINER"

Winter has again arrived in the northern hemisphere, bringing with it real dangers lurking and waiting to damage or destroy our musical instruments. Since bluegrass musicians all play some kind of acoustic stringed musical instrument, I want to discuss the special dangers we should all understand, and some of the simple steps that can be taken to guard against damage to your mandolin, guitar, banjo, dobro violin or bass.

To begin, let me explain that as a general rule, the higher the quality of your "axe", the more important it is to take special precautions to guard against the damage that can happen in the dead of winter. The reason for this is because high quality stringed instruments are built much more delicatly in order to produce increased volume and fuller, richer ranges of tone coupled with enhanced playability.

To be specific, this means that the tops and backs of guitars are made as thin as possible from quarter sawn woods. At the same time the internal bracing of these instruments is shaved thin to be light and not impede vibration. The finish is usually lacquer or varnish and it too is applied as thin as possible so as not to hamper the sound producing ability of the instrument. The necks are shaped to be slender and comfortable to play. All of these points combine to make the severe winter weather especially dangerous for the good health of your favorite instrument.

Now, a very important point to understand is that it is not really the COLD of winter that is the biggest menace, although it is the direct cause of finish cracks and checking. Luckily from a playability standpoint, in most cases these are mainly cosmetic in nature. The real danger lies in the fact that when it gets cold, we humans turn on our furnaces, stoves, heaters and light the fireplace to warm our homes, cars and workplaces. This artifical heating makes the air very DRY, and this is what caused the vast majority of winter damage.

Instrument wood

It is necessary to understand a little about wood to fully comprehend why this is true. Despite its appearance, wood is not as solid as it looks. Wood is made up of millions of cells that held the moisture and "life blood" of the tree and helped move it from leaf to root. Most musical instrument wood is dried to a 7% to 10% moisture content. However, the wood will forever allow moisture to pass into and out of its structure. Each variety of wood has what is called its equilibrium moisture content (EMC). This is the moisture level at which the wood is at rest naturally at a given atmospheric temperature and humidity. It is totally different from the surrounding atmospheric humidity, but is affected by changes in the humidity. It is not constant. When the air is wetter, there will be moisture absorbed by the wood to a new wetter level, which is not the same amount as the moisture level in the air.

The EMC curve is different for each species of wood. When the instrument is made of spruce top, rosewood back and sides, mahogany neck with ebony fretboard glued to the neck, and nickel silver frets wedged into the fret slots, you have a veritable "tango" going on within the instrument when severe moisture changes occur! You have different amounts of stress going in different directions at the same time. THIS is where the pressures come from that result in the glue joints pulling themselves apart. And if the joints dont fail, the actual wood members can crack. This is also the action that is causing the fancy flame maple neck to twist itself like a corkscrew. Each of those curls in the wood represents a "wave" in the grain structure. This wave has a hard spot and a softer area. The moisture loss makes the hard area want to go one direction at one rate, while the soft area wants to do something totally different. The result is a warped, twisted or wavy neck, that will never go back to where it originally was. If you are very lucky, an expert repairman can remove the frets and plane the fretboard surface flat again.

There is a GREAT discussion of this subject of EMC in detail and much more in the book called "Understanding Wood, a Craftsmans Guide to Wood Technology" by Dr. R. Bruce Hoadley. This book is available from the Stewart MacDonald Co. I highly recomend it to anyone who's interest has been sparked by this discussion!

To finalize the EMC point, if the relitive humidity changes or the temperture changes, the EMC for any piece of wood will change slightly. But all fall within a fairly small "window" on the charts. Here is the example right out of the book. It is very relative to our instrument topic! Using white (Adirondack) spruce as a sample, with the humidity at 50%, the EMC of this wood is 9%. If the humidity changes to 25%, the EMC will move to 5%. This will produce stress!! If the humidity then goes to up 75% the EMC will be 14%. The table below shows the same data in an easy to absorb way.

Atmospheric humidity Wood EMC
75%, fairly wet 14%
50%, median 9%
25%, fairly dry 5%

It is important to realize the relative humidity in a home in winter can easily be below 10%. These conditions are a prelude to possible disaster.

Most instrument makers strive for a workshop environment of about 40% humidity. This is compatable with most instrument wood EMC which is around 12% inside the wood at this shop humidity. This allows instruments to be shipped worldwide to slightly higher or lower humidity ranges with little or no concern.

If the guitar, mandolin etc. is exposed to higher levels of humidity the wood will absorb some moisture. If the humidity drops the wood will release moisture to the air. Centuries of expierence has shown that instruments are relatively unaffected by exposure to higher humidity levels (as far as damage is concerned). However, moisture loss is another subject! Again, experence has shown that when humidity drops extremely low or extremely fast, the resulting loss of moisture and shrinkage of the outer fibers of the unfinished wood surfaces (like the inside of a guitar or a fretboard) while the inner fibers of that piece of wood are still moist and unshrunken causes severe pressure inside the wood and distortion of the components. The results can be glue joints coming apart, cracks, warped, twisted necks, loose braces and loose and uneven frets. The tops of wood bodied instruments can drop so much that the strings will buzz. Often these strange buzzes will disapear when the humidity raises again. A very common example of damage due to differential expantion is on acoustic guitars with cracks around the pickguard. These occur because the wood top is shrinking and expanding at a rate different than the plastic pickguard.

Flamed maple resonator of a Desert Rose bluegrass banjo built by Scott Zimmerman To address banjo players concerns specifically, while banjos don't have the worries of the wood bodied instruments, banjos have very long and thin necks. These are often made of beautiful flame maple or other figured grain wood. The use of this wood is sometimes considered manditory for a top quality banjo. Unfortunately, figured wood is known to be extremely unstable at times, and it is quite susceptible to the dangers of heat, cold and humidity fluxuations.

The other primary concern is to the frets and the playability of the instrument. With the unfinished fretboard wood expanding and contracting with the weather changes, it is not uncommon for the frets to lift away from the fretboard causing any number of buzzes, rattles, muted notes and more. A very annoying problem can occur when the fretboard shrinks and the fret ends are exposed. This can give your neck the feeling of a saw blade! In the worst case, if your neck has decorative binding this shrinkage and exposed frets can cause the binding to come loose. And at times the frets can actually push through the binding! This is not a pretty sight! All these points add up to it being a good idea to be concerned about winter effects, or it may soon concern your repairman!

What to do

Now that you have some idea of the possible dangers awaiting your instrument in winter, I want to explain some very simple things you can do to remove the dangers and rest easy.

Most importantly, I feel very strongly that all acoustic instruments must be kept in a good hard case. A quality hard case is the only way to guard against lifes daily bumps & bruises. For those wanting to give their instrument the care it really deserves, this should be followed with a thermal case cover. These can reduce the dangerous effects of heat (and protect the finish from cold checking). With very few exceptions, standard high quality wood cases offer little to no thermal protection.

Having a good case is useless if you don't use it correctly. When you are not playing your instrument, it should always be returned to the case. And the case should always be latched closed and be kept somewhere safe from heat, This specifically means means away from heaters and stoves. The reason for latching is simple and twofold: to keep the instrument in a stable temperature situation and many instruments have been damaged severely when the unlatched case was picked up and the instrument falls out. (I did this with the first guitar I built back in the 60's. It cracked the top away from the side at the lower bout in addition to finish damage. - ed.)

Here is a good tip on how to use your case effectively. If it is necessary to play outside where it is cold, and your instrument has been in either a warm car or cozy house, take the instrument outside (in the case) about 30 minutes before you want to play. Leave it closed up in the case for about 20 minutes. Then 10 minutes before you want to play, open the case. This gives your instrment time to acclimate to the surroundings slowly with little shock. This is especially helpful in avoiding the 'spiderweb' finish checking common on old acoustic instruments. It will definitely help to keep the thing in tune too! Do the same thing in the reverse also, if you are going from cold to warm conditions, say from the trunk of the car to the gig. Either of these senarios might mean planning on geting there earlier than the last minute, if you want to minimize the possibility of hurting your instrument.

Hard data on temperature changes inside an instrument case is difficult to find; this link points to some data on the Colorado Case Company page. These tests were done while heating cases inthe summer, but the trend of the difference inside and outside the case are going to be similar to other situations.

One more important thing

OK, we have identified many of the primary dangers of winter, you have a nice case to keep your treasure in, and we have discussed the importance of using the case correctly. There is one more point to add which will bring it all together and allow you to rest easy.

Since the major danger is dryness, the logical solution is humidifying. There is now available a selection of modestly priced instrument humidifiers suitable for all instruments. Even the most expensive one is about the price of a medium grade capo.

These humidifiers are meant to be used inside the case when the guitar etc. is not being played. They all consist of some style of plastic housing, most with a sponge like material inside. You simply moisten the sponge, wring excess water out and insert the unit inside the instrument. The two most popular brands are the " Lifeguard" by Kyser. This is designed for acoustic guitars only and includes a cover for the sound hole. This offers complete control of the humidifying action. The other model is the "Dampit". It consists of a plastic tube with a sponge inside. This model can be used for all instruments. And comes in different sizes for violin, guitar, etc. Both these brands will cost between $10-15. At the low end is the Herco " Guardfather ". This is a small plastic box about the size of a pick holder, inside is a clay material. You moisten the clay and simply keep the little box in your case. It sells for a total of about $3!

An accessory to control the moisture in your case is like a gasoline pump to a custom built Ferrari. Even if you spend $150,000 on a car, it won't leave the driveway unless you keep gas in the tank! Humidifiers are the same, they can't work if you don't monitor the sponge to insure it has moisture to dissapate into the case enviornment. You will need to find out how quickly it dries out in your particluar situation. If you always find it dry when checking once a week, then you need to check and moisten it more often.

Peace of mind really is that cheap! If you buy one of these devices AND use it correctly (keeping it moist), you can drastically reduce the chances of sustaining structural damage to your instrument due to dryness. As an aside, for people living in the Great Southwest of the USA or any other similar desert climate, these units should be in your case yearround! If not easily obtained locally, they are available from most mail order companys like First Quality Musical Supplies and Elderly Instruments.

As a final note, I feel that all musicians should understand that owning a high quality acoustic instrument requires that you know how to care for it. If the simple things I have discussed were done by more people 60 years ago, there would be many more wonderful vintage instruments for us today! If you follow the advice outlined here, your favorite banjo, guitar, etc., will play better, last a long time and be a valuable asset in years to come.

Email to Scott at scott@sugiguitars.com
Surface mail to Scott Zimmerman, Stringed Instrument Technologies Ltd., 2-5-37 Shonicho, Matsumoto, Nagano, 390-0828 Japan, tel and fax 81-263-28-5080,

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