Humidity: Realistically, what's too high?

[hifivic]

I soak mine in tap water for 2 days, let them air dry.....typically dry in a couple hours and I'm good to go. Perhaps somebody could explain why someone suggested distilled water which I realize is suggested for soundhole sponge type humidifiers.

[Robin, Wales]

We are at 78% humidity today over here on the West coast of Wales. That's inside our old (1830s) stone house and outside (we've had the doors open and we have plenty of other unintended ventilation!). Our annual average humidity is around 80%. I doubt it has dropped below 65% this whole winter. My guitar is out of its case in an unheated room except for occasional evenings when I've lit the log burner in there. There are small amounts of mould around the old windows that I clean off every so often.

But the spruce braces inside my guitar are reading 2% humidity today on the little gauge I have to check our firewood? The built in old pine dresser in the room is reading 6%. My well seasoned firewood (in the basket in the same room) is at 12%. Some old bits of pine I have in the room opposite are at 10% and some old mahogany at 2%. Yet the room is sitting at over 70% and has been pretty much all winter?

So, perhaps there is more to this than meets the eye. I can't offer any scientific explanation just my observation that my guitar's set-up hasn't moved from last summer until now. Yet it lives leaning in a corner close to a window that has some mould on its under panelling in an unheated room except for the nights I light the log burner.

I'm not sure how much humidity is too much, nor how changes in air humidity react with guitar wood. My guitar is a Seagull S6 Spruce: perhaps the maple neck, cherry laminate back and sides and quite hefty spruce top are a particularly stable combination. Perhaps it is something else as my friends around here who have all solid wood guitars don't seem to have any issues either despite the relatively high humidity year round? No one has a humidifier or de-humidifier and they have there guitars out of the cases all the time. So I'm not sure that high humidity is as much of a problem as perhaps low humidity. Also, how much does the water content of the wood within a guitar actually change and how much change actually has a discernible effect? Perhaps, the age of the woods used to build a guitar is the most significant factor? Younger woods, particularly Far East or African woods, may more susceptible to drying out, I don't know?

Anyway, I think there may be more to this than the sales literature of humidifiers point out.

[KenL]

Originally Posted by MrBJones

Here in the Dallas area, we've had an awful lot of rain and damp weather. RH indoors has been above 50% for a while, sometime into the low 60s. At what point should the guitar go back into the case where it's not as humid?

If you could ship me about 15% of your humidity in a big box, then we would both be just about right.

Very dry up here in the Rocky Mountains.

[Dbone]

Originally Posted by hifivic

I soak mine in tap water for 2 days, let them air dry.....typically dry in a couple hours and I'm good to go. Perhaps somebody could explain why someone suggested distilled water which I realize is suggested for soundhole sponge type humidifiers.

Mold considerations from what I understand.

[Wellington]

Where I live it gets into the 20’s in winter and as high as the mid 70’s in summer, I humidify in winter once it’s 30 percent or lower, but I’ve never dehumidified, but it does make me nervous when it stays in the b 70’s for a few days but I’ve never noticed an issue other than the sound of the guitar changes, gets a little dull to my ears.

[KevinH]

Originally Posted by Robin, Wales

....Perhaps it is something else as my friends around here who have all solid wood guitars don't seem to have any issues either despite the relatively high humidity year round? No one has a humidifier or de-humidifier and they have there guitars out of the cases all the time. So I'm not sure that high humidity is as much of a problem as perhaps low humidity. Also, how much does the water content of the wood within a guitar actually change and how much change actually has a discernible effect?...

Interesting observation. Have you noticed the action increasing, or the dead sound often attributed to high humidity? I suppose if it's always that high it might be hard to see any changes.

[Robin, Wales]

Originally Posted by KevinH

Interesting observation. Have you noticed the action increasing, or the dead sound often attributed to high humidity? I suppose if it's always that high it might be hard to see any changes.

I do my own set-ups and so have all the tools (nut files, straight edge, feeler gauges, truss rod keys, accurate gauges) and have not seen a summer - winter difference (our humidity is pretty uniform throughout the year.) And I'm not sure about the dead sound attributed to high humidity. I chose my guitar because it had the most lively tone of the ones I tried out in various Scottish guitar shops. It is very bright. I really have no idea if living somewhere with constant high humidity makes a difference to tone? I do wonder if the seasoning and therefore stability of the woods used for building is the biggest factor in how well a guitar handles humidity changes? I expect that a lot of wood used in guitar building is quite young (I have seen this myself with the fretboards of Far East guitars).

I don't have any answers about all this just more questions!!!!

[charles Tauber]

Originally Posted by Robin, Wales

But the spruce braces inside my guitar are reading 2% humidity today on the little gauge I have to check our firewood? The built in old pine dresser in the room is reading 6%. My well seasoned firewood (in the basket in the same room) is at 12%. Some old bits of pine I have in the room opposite are at 10% and some old mahogany at 2%. Yet the room is sitting at over 70% and has been pretty much all winter?

What is likely happening is that the "little gauge" you have for checking moisture content in firewood is checking for what it says: moisture content in the wood. Wood/lumber for fine woodworking applications is usually dried to around 6% or so. (The moisture content of wood in a tree can well exceed 50%.) I'd hazard a guess that the "little gauge" isn't very accurate or precise as there isn't likely as much variation as you are reading in the moisture content of wood that has been equally acclimatized to its environment.

The relative humidity of the air in your environment is measuring something else altogether: one is apples, the other oranges.

[MrBJones]

Originally Posted by hifivic

I soak mine in tap water for 2 days, let them air dry.....typically dry in a couple hours and I'm good to go. Perhaps somebody could explain why someone suggested distilled water which I realize is suggested for soundhole sponge type humidifiers.

Mineral content of tap water would soak into them, changing the properties of what's inside.

[DesertTwang]

Unless they're hermetically sealed (99.9% aren't), your cases equilibrate with their ambient humidity, so it makes no difference whether your guitars are inside or out in the open.

[Robin, Wales]

Originally Posted by charles Tauber

What is likely happening is that the "little gauge" you have for checking moisture content in firewood is checking for what it says: moisture content in the wood. Wood/lumber for fine woodworking applications is usually dried to around 6% or so. (The moisture content of wood in a tree can well exceed 50%.) I'd hazard a guess that the "little gauge" isn't very accurate or precise as there isn't likely as much variation as you are reading in the moisture content of wood that has been equally acclimatized to its environment.

The relative humidity of the air in your environment is measuring something else altogether: one is apples, the other oranges.

Thanks Charles,

I appreciate that my gauge is 'out' or at least not definitive and that there is going to be a difference between water content of wood and air humidity. That point about building at around 6% or so water content is interesting. I wonder what 'tolerance' factories allow themselves around this? Also, what effect time of year has on some builds. For example the Eastman factory in Beijing could build/ship guitars in Jan when the temp is below freezing and humidity is 40% or the same model could be built and shipped in July/Aug when the monsoon is on the temp is 20C and humidity 72%. The ship would then dock in say SF in the autumn and the stock get sold at a guitar shop in Seattle at Christmas - all without the guitar being humidified/dehumidified.

But the wood aging is perhaps the key point (perhaps?). We know that a large percentage of tropical woods are illegally harvested and so miss-sold to guitar factories as something they are not (to the point where Martin can only offer one model that's actually FSC certified - ie the full provenance of most of their wood is unknown). And, of course, Gibson has been prosecuted over this issue. And with a guitar made in China you really don't know anything about the wood as China has not been so heavy handed yet on their suppliers, but they have in the last couple of months said they will crack down on illegal wood used (and I expect it will be quite a 'crack down!'). So, I wonder if folks are having to humidify guitars to stop their set-up moving because the wood was too young at the point of building?

[charles Tauber]

Originally Posted by Robin, Wales

That point about building at around 6% or so water content is interesting. I wonder what 'tolerance' factories allow themselves around this?

Wood is a hydroscopic material, which means that it absorbs and desorbs moisture in response to its environment. Anyone well-versed in working with wood as a material is well aware of that and the technology surrounding proper drying of wood and seasonal movement is well-known. Instrument making is just a small subset of those those who use wood as a material from which to make things.

Most engaged in fine woodworking either control the humidity (and temperature) of their shop environment or work seasonally to avoid the difficulties of working with moving wood.

Most large commercial woodworking facilities/factories control temperature and humidity year round. I don't know about Eastman, specifically, but I would be very surprised if they did not.

Most large - and small - guitar manufacturers make guitars in a stable humidity that is chosen to be a little below the average humidity where the guitars will likely live. For most, that is in the low to mid 40% range.

If you live in the desert, where the humidity is/or can drop to 15%, you are going to likely have problems if you don't humidify to maintain the 40ish % range. Similarly, if you live in a rain forest where your humidity is in the 90's, you will likely also have problems if you don't maintain the humidity closer to the 40ish % range at which it was built. (If you live in a rain forest, you'd be better off having one made locally at humidity levels consistent with your locality. Ditto for a desert. Some small manufacturers will adjust the humidity at which they build to suit the specifics of where the guitar is going to live.)

The ship would then dock in say SF in the autumn and the stock get sold at a guitar shop in Seattle at Christmas - all without the guitar being humidified/dehumidified.

Once it leaves the factory, it is the responsibility of those in the "supply chain" to ensure adequate temperature and humidity control of an instrument. That includes multiple shippers, warehouses, trucking, distribution centers and, finally, retailers. When purchased, it is then the responsibility of the buyer.

But the wood aging is perhaps the key point (perhaps?).

Wood is dried and wood is "seasoned", two different things. When cut, wood can exceed 50% moisture content. It must be dried to 6 to 8% or so for most fine woodworking applications. This can be done very quickly, for some species, in a kiln, or can be done slowly in air. (The rule of thumb for air drying is about one year of drying per inch of lumber thickness.)

Seasoning, or "aging", of wood is a change in the chemical composition of the wood that naturally occurs slowly over time - 20, 50 or more years. It has little to do with the moisture content of the wood. In recent years, some manufacturers have attempted to speed up the seasoning process to mimic the changes in composition of wood by heating wood in the absence of air, a process called torrefaction. https://en.wikipedia.org/wiki/Torrefaction. The jury is still out on doing that.

So, I wonder if folks are having to humidify guitars to stop their set-up moving because the wood was too young at the point of building?

It is a given that wood - regardless of species - must be properly dried and in equilibrium with the environment in which it is being made prior to making instruments from it. I have no reason to believe that Asian guitar manufacturers making guitars for sale in the West are not doing so. Are we in the West seeing an epidemic of cracking Asian-made guitars? Not that I know of.

Years ago, I toured a fine furniture "factory" in Thailand. It was a concrete slab with a roof. Workers worked in the open air while sitting on the floor to intricately hand-carve teak components for tables, cabinets, etc. I've seen many such pieces in North America, many of which have cracked panels. They crack due to the change in environment (humidity) between Thailand and North America and, perhaps, how they were constructed, not allowing wood movement. Similarly, I've seen many Chinese rosewood cabinets with doors that have shrunk to the point that their panels no longer fit their frames. Again, change in environment is the cause. Whether or not these factories have since modernized, I don't know.

In the huge quantities in which large guitar manufacturers consume wood, much of their material is not likely seasoned for long. Seasoning of wood, and its influence on instrument tone is somewhat subjective: proper drying of wood is not. Proper drying of wood is a practical necessity.


Keep in mind that in recent years we are seeing a large number of guitars being manufactured from woods that would have been traditionally rejected. (To be clear, not non-traditional species of woods.) A good example of that is using slab-cut domestic black walnut. It will undergo seasonal movement about half again as much as that of quarter sawn walnut, likely requiring greater humidity control to prevent its cracking. Black walnut is a domestic hardwood, grown, cut, dried and sold domestically: one can't blame international black market forces for that. Slab-cut wood is cheaper. Part of the modern obsession with humidity control is due to using pieces of wood - not species of wood - that are not well-suited to making guitars.


A few years ago, I made a curly maple cutting board for a customer. It was 10" wide and made from a single piece of maple, one that I have had for 25 years. It was well dried and well seasoned. I provided the customer with explicit instructions for its care - she had previously destroyed wooden cutting boards by putting them in the dish washer. A few months after receiving the cutting board I made for the customer, the customer sent me photos of the cutting board that was now riddled 2" long cracks in each end. She had not followed the simple instructions for care that I provided her. My point is that one must care for fine objects made of wood. If one doesn't one risks damage to those objects. That is not something new in modern times.

[Robin, Wales]

Thank you so much for the time you have put into your response Charles. That is great information and very much appreciated.