Flamenco Graf-Martinez

Guitar Care and Storage

Relative Humidity

Back when I still ran my guitar shop, most repairs to damaged instruments always had to be done in January and February. Not only were warped necks, sunken tops, and cracks in the neck and fretboard common, but cracks in the top, back, and sides were also very frequent. The damage to electric guitars wasn’t as severe, since they’re usually completely—or at least mostly—“sealed.” Damage to cheaper acoustic guitars was also limited, since their backs and sides are made of veneer or plywood.
Why specifically at this time of year? Well—these are generally the coldest months, when the outside air can absorb the least moisture due to its temperature and, more importantly, when the heaters are running at full blast in the buildings and rooms where we spend our time. In other words, relatively dry air is drawn into the buildings, where it is heated without any moisture being added. This is what we refer to as relative humidity (RH).

The Carrier diagram according to DIN 4108, also known as the saturation curve, illustrates the relationship between the maximum water vapor content, relative humidity, and temperature.

Cold air can hold far less water than warm air. This means that, for physical reasons, cold air is drier. For example, air at 22°C can hold more than 16.7 g of water per kilogram of air, whereas air at 0°C is already saturated at less than 3.8 g of water per kilogram of air.
In winter, therefore, the cold outdoor temperatures result in very dry air. However, the air in our living spaces is often even drier. When we ventilate, we let the winter air into our living spaces. While the absolute amount of water remains the same, the air’s potential to absorb moisture increases significantly as it warms up. If the air is not humidified at this point, the relative humidity drops rapidly.

Cracks in the hardwood floor caused by dryness.

Hygroscopicity — or the shrinkage and swelling of wood.

Now the material used for our instruments comes into play—wood. Wood is a hygroscopic material that adapts to its environment. It “breathes.” It absorbs or releases moisture. As a result of these processes, the wood shrinks or swells—a phenomenon known as “working.” Not only our instruments, but also our furniture, our wooden floors, parquet, and even paintings and our health suffer as a result if they are not protected or if no countermeasures are taken.

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The Shrinkage of Wood
Example: The shrinkage rates of individual wood species.
Wood shrinkage.
Source: *The Guitar and Its Construction* by Franz Jahnel (1973)

Wood contains “free water” and “bound water.” The “free water” is found in the water channels (tracheids and tracheary elements) of the wood, which transport water from the roots to the crown. This water is the first to be removed from the wood during the drying process. “Bound water” is located between the rows of micelles in the fibrous tissue. When water is removed from these cells, the cellular structure changes. However, as soon as the environment—that is, the air—changes again and contains more moisture, the water is reabsorbed. This ability of wood to release moisture to the outside when the outside air is dry and, conversely, to store moisture back inside when the outside air is humid is called hygroscopicity. The expansion—that is, the increase in the wood’s volume—is called swelling; when moisture is removed from the wood below its fiber saturation point, it is called shrinkage.

The wood used by guitar makers, guitar manufacturers, and the instrument industry.

After the wood is cut, it is typically stored outdoors for up to 10 years. The guitar maker then selects pieces from this stock. However, most of the tonewood is kiln-dried. This shortens the long-term natural drying process to just a few days. But even in the artificial drying chamber, only the “free water” (see above) is removed from the wood. During air drying, a natural aging process takes place in which not only water is removed, but also oils, resins, proteins, starch, mineral salts, tannins, and pigments.
As a rule, guitar makers build their guitars in their workshops at a relative humidity of 45–60%. Of course, this also depends on the environment. Along the coasts of Spain, relative humidity is consistently 60–70%, while inland—for example, in Castile-La Mancha, the dusty region of Don Quixote—it is very dry in the summer. In Madrid, relative humidity can drop to as low as 40% in the summer. José Ramírez was the first to build guitars in his workshop at a relative humidity of 63%.
If you buy a master-crafted guitar from a luthier or even at a specialty store, you should ask under what climatic conditions the guitar was built. However, with mass-produced and industrially manufactured guitars, it is rarely possible to get an answer.

José Ramirez in Madrid (1976)

Wood Protection – Finish

Another crucial factor is how the guitar is protected against climatic and mechanical influences. The finish serves to protect the wood from external influences, preserve its resonance, and give it an elegant and refined appearance. If the wood of a master-crafted guitar is finished with a shellac polish (en: French Polish, es: goma laca), it offers little protection against mechanical damage, such as nicks and scratches, since the polish consists only of wafer-thin layers applied daily over weeks using a linen ball. It remains the best option for the instrument’s sound. Since the application process is an art form and requires a great deal of work, it is only worthwhile for master-crafted guitars. The wood is now protected on the outside, but the interior of the body and the fingerboard remain untreated. Since the shellac granules are dissolved in alcohol, one should be careful with alcoholic beverages while playing the guitar. Body sweat, especially when combined with deodorants, also takes a heavy toll on the finish, roughening it, causing it to peel, or making it appear dull.

In addition to this elaborate finish, there are many others, such as nitrocellulose, two-component, and modern synthetic finishes, which are widely used. On solid-body electric guitars, everything is usually finished except for the fretboard. So everything is sealed, so to speak.

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A visit to the workshop of Manuel Bellido (Granada) and his sons Jesús and Mauricio.

Where to Store Your Guitar—When You’re Not Playing It?

It goes without saying that you should treat your guitar with care and protect it from bumps, knocks, and other mechanical stress. Most of the time, it’s best kept on a guitar stand or in a case. Even when transporting it, you should take care not to put too much strain on the instrument. Far less attention, however, is paid to climatic influences such as cold and, above all, heat. The cold itself doesn’t affect the guitar as much as the dryness that comes with it. More on that later. Warmth, or even heat, isn’t good for the guitar in the long run. If you leave the guitar in the sun for a long time, or leave it in a car that’s been parked in the sun for several hours, don’t be surprised if the neck has warped or the various woods used in the guitar’s components have warped.

At a luthier’s shop in Granada, I once saw a guitar that was waiting to be repaired, completely disassembled and lying in its case. Back then, most guitarreros (that’s what a guitar maker is called—the guitarist is the guitarrista or tocador) still worked with bone glue or hot glue. As a result, at 70–80 degrees inside the car, the glue could no longer hold anything together, since it had simply returned to a liquid state.

As mentioned above, dryness is the greatest threat to our beloved instruments. That’s why we should pay the utmost attention to storage. Due to completely sealed and insulated windows in buildings, there is virtually no air exchange in indoor spaces these days. Modern central heating systems, which run at full capacity when temperatures drop below freezing, completely dry out living spaces. It’s even worse with underfloor heating. It’s not uncommon for the relative humidity in a living room with a temperature of 20–22 degrees to fall below 30%. As mentioned above, levels below 40% are already critical for a guitar.
But air conditioning also completely strips the air of moisture. Every car is equipped with it these days. It’s a mistake to assume in the summer that nothing will happen to your guitar inside an air-conditioned car. Dryness increases rapidly when the air conditioning is turned on. You can tell this is happening when the windshield fogs up in rainy weather. Turn on the air conditioning briefly, and the windshield clears up—meaning the moisture is gone.

Ways to protect your guitar from dryness.

The simplest solution is to store it in a room that isn’t heated too much, or to create a suitable climate in the room itself—one in which we, the plants, and the instruments feel comfortable. Having many plants in the room (a greenhouse would be ideal), which are watered more often in the winter, can make a big difference. However, this can also be balanced out by using a so-called humidifier.
There are three types of humidifiers, which differ primarily in the technology they use to distribute moisture into the air: surface evaporators, evaporative humidifiers, and atomizers (ultrasonic devices).

For decades, even back when I ran my guitar shop, I used Venta humidifiers. They’re the most expensive, but they’re also quite good. The last model I bought broke down after just a few years—more specifically, the sensor buttons stopped working. When I contacted the manufacturer about a replacement, I was told that the price of this button unit was half the original price of the unit. That was just too ridiculous for me. So-called “quality craftsmanship” from Baden—breaks quickly—and (over)priced. I have to admit that. Without further ado, I bought a nebulizer, which is still doing its job to this day. However, since our tap water has a very high calcium content, a new filter has to be purchased every year. This can be avoided by using distilled water or the water from the clothes dryer, which my wife has been collecting ever since. Since my guitars are in a display case, a relative humidity of 40%—which the humidifier maintains constantly—is more than enough for my study.

A cozy spot for my guitar

The display case, which I built myself from solid, laminated beech wood panels, is completely airtight. In this display case, it’s relatively easy to maintain a constant climate and humidity level in both summer and winter. The solid wood stores humidity and compensates for fluctuations if I don’t refill the humidifiers in time. The moisture comes from two containers filled with floral foam, also known as floral moss or simply “Mosy.” This moss absorbs a great deal of water and distributes it continuously and evenly throughout the display case. When it’s very dry, I refill the water once a week. In the summer, everything regulates itself. If you use distilled water, the moss doesn’t calcify as quickly. Another way to humidify the display case would be to use a so-called humidor from the cigar section. However, the moss is the most affordable solution.

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Display case under construction

Photo 1: Homemade display case; Photo 2: Guitars in the closed display case; Photos 3 + 4: Display case open; Photo 5: Floral foam; Photo 6: Smart Home app; Photos 7 + 8: The humidity sensor.

“Smart Home” technology has now made its way into the realm of instrument storage and climate control. In my opinion, not everything in a “Smart Home” is “smart” or practical. But I find this technology very handy for monitoring my guitars. A temperature/humidity sensor continuously transmits the environmental conditions inside my guitar display case, and I can check the readings on the app at any time. What’s really cool is that the app can be programmed to emit an audible alert (in my case, a voice saying, “The humidity is below 60%”) to warn me that the humidity is too low.

When is it too dry?

If I can afford a guitar in the mid- to high-end price range, I should also be able to afford a hygrometer.
The cheap ones from hardware stores or discount stores do the job, but they’re usually inaccurate. The best option is still the hair hygrometer. It actually uses a strand of human hair—preferably a blonde woman’s hair—which, via a lever mechanism, indicates the humidity level on a scale.

However, this hygrometer needs to be calibrated from time to time. There are now also very good digital devices available, but they come at a price if they’re to be reasonably reliable.

Last Saturday, we had a local temperature of -1° C, snow showers, and a humidity level of 84%. That only happens in winter during showers. If it had been dry, the relative humidity would likely have been around 40%. In my study, where my guitars are kept, a cheap hygrometer read 43% humidity. The humidifier read 44% and had shut off, as I had programmed it to do so. That level is absolutely sufficient for me. The guitar display case showed exactly 57%.

My Conde sounds best at this level. With this guitar, I must under no circumstances let the humidity drop below 50% or rise above 60%, even though it’s already 20 years old. The nine-year-old Ramirez isn’t affected by humidity, but it still shouldn’t fall below 45%. My flamenco guitar, which I built myself in 1988 (back and sides: cypress from Granada; German spruce top; neck: Honduran cedar) has been through so much. It’s spent over 100,000 km in a car, been stored in cold airplane cargo holds, has a few cracks in the top and back, and feels comfortable at 40% and above. Since it doesn’t sound good above 50%, I take it out of the display case an hour before I want to play it.

How can I tell if the air is too dry for my guitar?

Sharp, protruding fret edges are a clear first sign that the air is too dry. This is because a lack of humidity causes the unprotected, unvarnished fretboard to shrink, while the metal of the frets does not. As a result, the ends protrude from the sides. The simplest test is to run your fingers along the sides of the fretboard. You’ll be able to feel whether the sharp-edged frets are sticking out.

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Photo 1: The frets protrude beyond the shrunken fretboard. Photo 2: The frets have caused the finish on the fretboard to crack because the fretboard warped at some point. Not a major issue, but an early warning sign that it was too dry at some point.
Video: If you run your fingertips along the fretboard, you can feel the sharp-edged, protruding frets.

The Guitar Top

Excessive dryness can also be recognized by changes in the guitar top. Under normal conditions, it is very slightly arched outward. It is convex. If it shrinks, it flattens out or even caves in; it becomes concave. This helps to somewhat compensate for the loss of moisture. However, the string action also changes because the bridge sinks along with the top. This can range from 3 to 5 mm, depending on how pronounced the top’s arch is.

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Arched, or convex, top. String action at the bridge.

If nothing is done, the wood will continue to expand and contract until it finally cracks. These are the infamous shrinkage cracks. At this point, the guitar should be taken in for repair immediately. The luthier restores the necessary moisture to the instrument until the gap closes again, applies a small amount of glue to it, and braces the top with clamps. Often, a strip of parchment soaked in glue is also applied to the inside of the crack in the top. Since the parchment shrinks as it dries, the crack is effectively sealed. If you wait too long to have it repaired, or if you don’t notice the crack, it is usually necessary to insert a splint and glue small wooden pieces—known as “diamonds”—to the inside to restore the top’s original stability. However, these steps cause the repair costs to rise significantly.

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The Guitar Neck

If moisture is drawn out of the neck and fretboard over an extended period, it’s usually impossible to correct a warped neck. With high-quality instruments, the luthier will level the fretboard with a plane after removing the frets. In the worst-case scenario, the fretboard will need to be replaced. Of course, this only applies to nylon-string guitars that do not have a metal truss rod installed. But even with guitars that have a steel truss rod—that is, all acoustic and electric guitars—it’s often frustrating when the neck has warped due to dryness and nothing can be done to save it. Worse yet—if the neck is twisted, it’s unfortunately too late. In that case, too, the only solution is to replace the fretboard or install a completely new neck.

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Photo 1: Every guitarist’s nightmare—a bent, sagging neck. Photo 2: It doesn’t get any worse than this—a twisted neck.

Traveling with a Guitar

Guitar in the car
Guitar on the plane.
Guitars in the trunk.

When I’m traveling by car or plane, I loosen the strings slightly. That way, if something were to happen to the guitar due to mechanical or climatic factors, the damage can be minimized somewhat. To be on the safe side, no matter what time of year it is, I always keep a small hygrometer (included with high-quality cases) and two humidifiers in my case—one on the body and one on the headstock. I don’t think much of humidifiers that are inserted into the soundhole, since they only humidify the interior of the body.

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Hygrometer in the guitar case
Humidifier for the guitar case
Humidifier for the guitar case

Just be careful!

I was one of the first people to import high-quality master-crafted guitars from Spain—primarily Andalusia—here to Germany back in the 1980s. I transported countless instruments here to my guitar shop at the time. At first by car, later by plane, or the guitars were simply shipped via a freight company. I’ve never lost a guitar. Nor has an instrument ever warped or been damaged, since I always took the utmost care during transport. During my numerous concert trips and tours, which I’ve been doing for decades, something happened only once. After the concert, someone knocked my guitar—which was in its case at the edge of the stage—off the stage. As soon as the tour ended, I took it to Josip Krog in the Taunus region, who repaired the guitar so beautifully that the damage was no longer visible and the sound hadn’t changed at all. On the contrary, I even thought it sounded better afterward. Unfortunately, the culprit could not be identified, so I finally had to file a claim with my instrument insurance. But the so-called “night clause” kicked in, and I was left to cover the costs myself. Since then, I’ve never taken out instrument insurance again—and I simply take the utmost care of my instruments.

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