Mayos Music
Guitar Lessons and Instrument Repair

Acoustic Guitar Maintenance & Issues


Here at MayosMusic, in addition to offering great guitar, bass, ukulele, banjo and autoharp lessons, plus complete luthier services that include guitar, string instrument and amplifier repair/restorations, we are also a great resource service.

Acoustic guitars need proper care and maintenance to play and look their best (and maintain their value). Sometimes issues can come up that need to be addressed. So let's discuss some of those now.

I. Humidity

Guitars are made of thin wood which is easily affected by humidity (moisture). When humidity increases, the moisture content of the wood rises, causing the wood to expand and swell. High humidity combined with high temperatures may cause glue joints to weaken and possibly open. Humidity can also damage finishes by allowing mildew or mold to grow on it, by making it milky and bubbled, by popping the finish off of the guitar, or by allowing metal parts to rust which can then stain the finish.

When humidity decreases, the moisture content of the wood lowers and if this happens too quickly, it can cause cracking and opening of joints as the wood shrinks and pulls apart. Wood shrinkage can also cause the frets to become loose.

Here are lists of possible issues of humidity related problems.

Symptoms of a wet guitar:
  1. Swollen guitar back.
  2. Swollen guitar top.
  3. Fretboard swollen (wider than the neck).
  4. Improper neck angle.
  5. Change in action (usually high).

Symptoms of a dry guitar:
  1. Back of the guitar looks flat.
  2. Sunken Guitar top (causing the action to lower).
  3. Fretboard shrinks in width causing the fret ends to extend beyond the edge.
  4. Forward bowing of neck.
  5. Hump in the fretboard where the neck joins the body.

II. Temperature

High temperatures can loosen glue joints, warp the neck (if the guitar is strung and tuned), and cause softening of the finish.

Low temperatures can cause checking and cracking of the finish, and even cracks in the wood.

Note: Rapid changes of temperature in either direction will cause the most damage.

III. Storage

I recommend storing your guitar in its case (hard case) when not being played. This will affect a more gradual change due to temperatures and humidity causing much less or even no permanent damage. The case will also help protect your instruments against physical damages and keeps it cleaner.

IV. Cleaning The Finish

Lacquer Finishes: Often, you only need a warm, damp cloth to clean your guitar. For grimier guitars, a good quality guitar polish (NO Silicone based polishes) may be needed.

Polyurethane Finishes: These finishes are very tough and may be cleaned with most household cleaners (409, Simple Green, etc.), but test in a small unseen spot first like the back bottom lower bout edge.

  1. Tuning Machine Maintenance & Adjustments

First, always check mounting screws and nuts every time you change strings, as they can work loose from vibrations, temperature and humidity changes. Don't over tighten. Most enclosed machines have a tension adjustment screw at the end of the tuning knob. Adjust to minimizes slop and play, and to a medium soft tension when you turn the knob. Open gear tuners should be lubricated once or twice a year. Use a clean heavy oil or very light grease (one that does not separate or dry to a shellac like varnish), apply, cycle each key a full rotation of the string shaft (13 to 26 rotations of the knob, depending), then wipe clean the excess.

VI. Strings

Different styles of playing require different types of strings. Different types of guitars require the correct type of string (for example, never put steel strings on a classical guitar).

A) Classical / Flamenco Guitars:
  1. Nylon strings in light, normal, and high tension, in traditional or ball ends.
  2. Silver coated nylon strings - Bright sounding.
  3. Bronze coated nylon strings - Mellower sounding.
  4. Clear nylon - Brighter sounding.
  5. Black nylon - Mellower sounding.

B) Steel String Acoustics:
  1. Bronze wound (80/20) - Yellow/gold in color, bright sound when new, loose brightness relatively quickly.
  2. Phosphor Bronze wound - Orange/gold in color, slightly more mellow than 80/20 bronze strings when new, but retain new sound longer.
  3. Silk & Steel (usually silver plated on the wounds) - most mellow sound, less volume, lower tension than solid core strings of equal diameter. Often recommended for very old vintage guitars.
  4. Coated strings - designed to last longer and be corrosion resistant, but tone is less bright than non-coated strings.
  5. Round core strings - Older design, though still around and common.
  6. Hex core strings - Newer design, intended to help reduce or eliminate the outer wrap slipping or twisting loose on the core.

VII. Inserting Bridge-pins & End-pins

Strings are held in place at the bridge base by the bridge pins. The pin slot must be facing forward to properly align the string on the bridge base. The ball end of the string must be pulled tightly against the inside of the top of the guitar before fully inserting the bridge pin. Do not hammer the pin into the bridge base. Your thumb pressure is all that is needed.

The guitar strap hooks on the End-pin. It is at the bottom of the guitar in the middle. Do not glue or hammer the endpin, instead twist slightly while pushing.

VIII. Truss Rod Adjustment

Most guitars have adjustable truss rods. Old Martins and some older Harmony, Kay, Stella, and other "makes" do not. Some modern and vintage guitars and basses (e.g., Rickenbacker) have double truss rods to adjust the bass and treble sides independently.

If the truss rod is too tight, the neck will back bow, which causes buzzing and "fret out." If the truss rod is too loose, then the neck will bow forward causing higher action. Adjusted correctly the neck will appear to be straight, but there still needs to be some measured relief. Truss rod adjustments should be made by a qualified Luthier or guitar tech.

IX. Action Adjustment (the Set-up)

A complete set-up and action adjustment should include:

  1. Prior inspection of the guitar for cracks, loose braces, bridge, keys, etc. (perform repairs as needed).
  2. Adjust the truss rod.
  3. Check all frets to be seated & tight.
  4. Top, shape and polish the frets.
  5. Adjusting of the saddle/saddle pieces
  6. Adjusting of the string slots at the nut
  7. Adjusting of the tuning keys
  8. Cleaning and then finally restringing and tuning.
  9. Final double check of the truss rod.

Note: The final adjustment is set by feel as no two guitars with set measured adjustments will play or feel the same due to differences such as scale length, fretboard radius, shape of the neck, fret size, string diameter (gauge), etc.

X. Neck Angle & Guitar Tops

The neck must have a good "neck angle" to the body of the guitar. Too much of a "flattened V" will cause very high string height. A neck-set will correct this problem.

Note: Correct neck angles will allow for correct saddle height. Too low of a saddle and the guitar will have less volume, less projection, and less sustain. Too high and the sustain will also be reduced due to the "break-angle" being past the optimum. The saddle needs to be within an optimal range while dialed in to the correct height for the strings over the fret board.

Regarding guitar tops, some bellying of the top is normal. Too much bellying-up and you have a problem. Likely a bad internal brace or bridge plate.

XI. Using A Guitar Humidifier

All quality acoustic guitars are made from solid woods and are most often built in a controlled environment where the relative humidity is 45-55%. A guitar humidifier should be used when the relative humidity falls below 45%. Products such as the "Dampit Soundhole Humidifier" work very well. There are even digital ones now that give a clear readout of the level.

XII. Traveling With Your Guitar

The guitar and it's fretted instrument family (Uke, Banjo, Mandolin, etc.) probably travels more than any other instrument in the world. Make an effort to protect your investment. Some recommended suggestions when traveling are:

  1. Car Travel - Avoid the trunk of the car. Trunks are neither heated, nor cooled/vented, and thus temperatures can fluctuate from extreme hot to extreme cold. Also, the further towards the rear bumper of any car, truck or van your instrument is, the more it is subjected to a harsh and jarring ride.
  2. Air Travel - First loosen the strings (back off tuning about 4 half turns of the tuning keys). This will unload the tension on the guitar and if ruff-handled (dropped) it can often save cracking and breakage. Only travel with a hard shell case. Some airlines have the option to bypass normal baggage handling and instead the guitar can be tagged and hand carried to the plane at the boarding area.
  3. Insurance - Get it for your gear. Whether car or plane travel, accidents can happen. Ask your home owners and car insurance carriers what their policies are. If need be get separate insurance specific to instruments (look online).

XIII. Guitar Straps

High quality guitars with lacquer finishes can be adversely affected by the interaction with vinyl and synthetic straps. It is best to always remove the strap from your guitar after use and store separately.

XIV. Guitar Stands

A quality, durable and safe guitar stand is as important as a good hard shell case. Hercules makes a great line of quality and safe guitar stands that help prevent your instruments from falling off the stand.

Experience since 1968
Providing Guitar Lessons and Guitar/Amp Repairs in Southern California, South Bay Cities and Greater Los Angeles Area,
Located in Manhattan Beach, Ca. and Torrance, Ca.

(310) 955 - 0246