TL/DR
- Guitars are built at 45-55% relative humidity. Vermont homes in winter often sit at 25-35%.
- Buy a hygrometer. You can't fix what you can't measure.
- Best fix: humidify the room where the guitar lives. Second best: humidity packs in the case.
- Electrics are lower risk, but not zero risk.
- Notice sharp fret ends, lower action, cracks or a sinking top? Humidify properly for 2 weeks, then book a visit if you still have issues.
It’s that time of year again when the heat comes on, windows and doors get sealed up, and your living space becomes a desert landscape. This is bad news for your instruments, especially the acoustic ones. Last year, I had about eight folks’ guitars at one time in a radical re-humidifying closet. This is worst case scenario, and it breaks my heart for people when they bring in instruments in this condition. Please heed my warnings and take steps now!
Why Humidity Matters
Dry winter air is the primary cause of most of the common repairs I see. Wood cells hold on and release moisture (i.e. water vapor) based on the relative humidity of the space they are stored. Your guitar was built in a shop held at 45-55% relative humidity. A Vermont house in winter is often 25-35%. That’s a huge difference, and left unchecked can draw upwards of 150 grams of water out of your guitar pretty quickly – according to Taylor Guitar’s tech training documents.
As the wood dries it shrinks, mostly in the weakest point: around the sound hole. It begins to curl up like a spider, folding inward towards the hole. The sinking hole curls the neck and bridge towards the center. This deforms the wood, raises your action, peels your bridge off, creates cracks, and generally wreaks havoc on the structural integrity and playability. The fingerboard can shrink as well (this is the primary electric guitar risk), but the metal frets don't, so the fret ends will stick out and feel sharp.
Even For Old Guitars
Players like to say that old guitars "open up," and that’s both true and entirely relevant. Over decades the wood changes at a cellular level. The sugary compounds that grab moisture and dampen vibration (hemicellulose) slowly break down, so the wood gets lighter and begins to resist water transfer. The resins and sap inside the wood harden and crystallize, which stiffens the wood without adding weight. Years of string tension (about 160 to 200 pounds of pull plus the tension of playing) also let the fibers relax and settle.
Lighter, stiffer, more relaxed wood vibrates more freely, which is the clearer notes and longer sustain people chase in vintage guitars. Less moisture-grabbing material also means a 50-year-old guitar reacts less to humidity swings than a new one. Less reactive is not immune, and it's the instrument you can't replace. So, the same rules apply to old guitars.
Got a guitar that's been in a closet or case for a few years? It has been through those winters without you. Bring it in and I'll tell you straight whether it's worth fixing, and what it will cost, before I touch it.
Exactly What You Can Do
1. Get a cheap hygrometer. That's a relative humidity gauge. You cannot fix what you cannot measure. It’s not a perfect tool, but micro-accuracy is not the goal. You want to know if it’s 50% or 30%, not 50% or 51%. Put one in every room you store your guitars. I use the D’Addario one in my shop, but any of these are great: https://www.stewmac.com/search/?q=hygrometers
2. Humidify the room (best option). A room humidifier that holds the space around 45-50% protects every instrument in your house. Always over-buy the size, you want it to work effortlessly, not churn around the clock. Distilled water and regular cleaning for mold are recommended. I have found that tap water works just fine and a few drops of tea tree oil keep cleanings less frequent, but that’s my lazy-man’s advice. Also, watch the hygrometer! Too much humidity causes its own problems, so don't let it climb past 55-60%.
3. Use humidity packs (second best). Two-way packs in a closed case add or release moisture to maintain a 50% RH in the case. They only work if the guitar is actually in the case. Replace them if and when they get hard and thin (not fat and squishy). Here’s my pick:
4. Hybrid approach. If you have many instruments, it makes sense to humidify a room with the bulk of them, and use packs for the ones you keep around the house.
5. Avoid heat and sudden swings. Keep it away from vents, radiators, wood stoves and sunny windows. Never leave it in a cold car. When it comes in from the cold, let it warm up in the case before you open it. Treat it like it’s fragile. It is.
Some additional notes…
This advice is for acoustic instruments (which include semi-hollow and hollow-body electric). Solid body guitars are mostly safe, except fingerboards. Excessive, sustained dryness causes fret and neck problems. So, it’s not a bad idea to humidify them either. Unless you have a lacquered fingerboard. These are lighter colored, typically, and have a glossy sheen. Mostly seen on Fenders or Fender replicas. Those are nearly impervious to moisture.
Additionally, this is only for dry conditions. In the warm seasons in Vermont, you can generally leave your instruments out on the stand day and night. You may find the hygrometer goes out of range a bit overnight during these months, it’s fine as long as it returns to a safe range all day.
What If It’s Too Late?
Symptoms of sustained dryness include:
- Sharp fret ends along the edges of the neck
- Action (how high the strings sit over the fretboard) changing or buzzing
- A top that bulges below the bridges, or is sinking near the sound hole
- Cracks in the wood or finish, especially near the bridge
- A bridge lifting at the edges
- Seams, bindings or the top and back starting to separate
If you see any of it, don't panic and don't glue anything. First, humidify properly for about 2 weeks. Why? Because working on a dry guitar is not smart, and I’ll have to do that first anyway. Then, bring it to me for a look. Catching problems early is the key to reducing cost and damage.
Reply with Questions
Have a question about your setup at home? Just reply to this email. If you've noticed any changes in your instrument, Book Now. Inspections are free. Playing a gig soon? Tell me the date and I'll tell you straight whether I can make it. Know a player who should read this? Share it, please!