Neck bend - (alert, not another do you need to humidify your guitars discussion please!)

Gear & Tools Talk šŸŽø Guitars, Instruments & Maintenance
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Please note: This is not yet another thread about whether you need to humidify your guitar or not, or how you do it.

However, hereā€™s a surprising (at least surprising to me) observation from the Xmas / New Year holiday period. I own 4 guitars: 2 squire teles (one completely renovated/modded by me), 1 home built partscaster Strat and a recently bought (November 2025) Yamaha Pacifica standard.

My teles and partscaster are really stable and since doing a complete setup on each, I have not had to re-adjust the truss rod again - they seem very stable during humidity changes and I donā€™t notice any great difference between summer and winter.

However, surprisingly, the Pacifica neck seems to be very sensitive to humidity and Iā€™m wondering why. Our apartment, has thermostat controlled underfloor heating and temperatures are very stable at 22C throughout the winter. But without using a humidifier, the apartment is extremely dry. When I got the Pacifica, the neck profile was strongly concave and required considerable truss rod adjustment and a thorough setup. Then because the apartment was getting very dry, I started using the humidifier to keep humidity at around 50%. I was confused because I realised the action wasnā€™t good anymore on the Pacifica (while doing the WYWH December challenge) and was so low I was getting fret buzz. I could see the neck had flattened even more with the humidity & I didnā€™t have time to reset it. I just did my WYWH challenge with one of my teleā€™s and then it was the Xmas break.

We were away for over 3 weeks, shut off the humidifier, and in our absence it was very cold and dry outside and the apartment humidity went right down to 15%. We canā€™t switch off the heating in our apartment as itā€™s on or off for the while building, regulated by an external thermostat - so temperature stayed constant. On our return, all my guitars were OK, except the Pacifica, which had such a strong concave neck relief again that the action was really high and it was unplayable. Not thinking much, I put on the humidifier again and sure enough, in 2 days, the neck relief was straight again - like it was before leaving. So in this case, Iā€™m talking about a substantial change in neck relief between 15-50% humidity. Temperature has been relatively constant during this period. So itā€™s definitely humidity that does it.

So what Iā€™m wondering is why is the neck so sensitive to humidity changes when the other 3 guitars are not? All are maple necks. My partscaster has a very high quality roasted maple neck which as been sanded and oiled by me, and it has a relatively thin untreated rosewood fretboard. The Squier tele necks are a bit thinner, all maple necks (not roasted) - one is covered in thin satin lacquer (standard affinity squire production) and the other has been sanded and oiled by me. The Pacifica neck has a considerably thinner piece of maple, that is also lacquered with a thin satin lacquer, but the big difference is that it has a substantial thick slab of rosewood for the fretboard (itā€™s also untreated).

I donā€™t think itā€™s anything to worry about that the neck is so sensitive to humidity changes - I hope? (especially as the Pacifica standard has a super easy truss rod adjuster wheel at the neck heel - which I wish all guitars had). However, as Iā€™m interested in guitar construction, Iā€™m wondering if the thick slab of untreated rosewood absorbs and releases humidity easily and thatā€™s what alters the neck relief so much during humidity changes? Itā€™s the only obvious difference I can see in the neck construction compared to the other guitars. I canā€™t imagine that much humidity can be absorbed though lacquered maple - it seems that would be a good seal to keep our moisture. As far as I know, rosewood fretboards are untreated so thereā€™s no lacquer or oil surface seal to keep our moisture.

I would be interested to know what other people think might be causing this - without people going into long discussions about how they humidify their guitars / rooms which has already been extensively discussed on the forum.

All the best, Ian

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A few wild guesses:

What kind of case do you use for storing the Yamaha? Or is it a bag?
In what cases, or bags do you store your other guitars?
Maybe the maple used by Fender, isnā€™t the same as the Yamaha? Different countries, different climates where the trees grew?
Iā€™m not sure if a fretboard can manipulate a piece of wood thatā€™s much thicker. Wouldnā€™t it come apart from the neck?
Maybe itā€™s more temperature related, instead of moisture? (Again, maybe different sorts of maple?)

Again, all just wild guesses, but who knows. It might help.

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They are all hanging on the wall in the same environment. I donā€™t keep them in cases.

Indeed, I hadnā€™t thought of that.

Good point.

Well since they all experience the same temperature, I doubt it. All the humidity fluctuations were with a stable 22C temperature.

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So just from a materials/mechanical standpoint, if you have a slab of wood that is made of two different wood types glued together, I can imagine that slab bowing as it absorbs humidity (or dries out). The reason is different woods can expand different amounts for a given change in humidity and if you have 2 pieces of such wood glued together, youā€™re going to get some bowing. This is all theoretical, of course. I donā€™t know anything about the relative water absorption properties of maple and rosewood, but this is the kind of thing that could happen.

Btw, this (two different woods glued together) seems to describe both your Yamaha (which bowed) and your partscaster (which did not). Maybe the difference is due to the greater thickness of the rosewood on the Yamaha?

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There are plenty of potential variables ā€¦ here are a few more ā€¦

Cut of wood - quarter sawn, slab sawn etc.
Tension on/type of truss rod (single action / dual action?)
How seasoned the wood is.
Whether skunk stripe added.

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Iā€™m throwing out some ideas as well - no certain conclusions for your issue.

  1. I have an Ibanez s-style with a thinner neck than anything else in my collection. It moved a lot when I first got it. I live in Arizona and my house humidity is generally around 25-30%, but can go under 20% and over 70% throughout the year for a day or two.
  2. I do not put my electric solid body guitars in a controlled case. They sit out.
  3. I do place my archtop in a case when the house humidity is outside 40-60%.
  4. The archtop tuning moves all over the place with humidity changes, but the neck relief seems solid. this neck is wider and moderate thickness with lacquer finish topped with an oiled fretboard. I have seen tuning move with atmospheric pressure as well, but havenā€™t correlated with humid chages that also occur at those times. No significant relief change in the 8 months I have had this.
  5. The thin Ibanez bolt-on neck also needed to be tightened down after about 5-6 months of climatizing to my house. Tuning moves a little more than other necks, but no major relief change. The neck is a light satin finish with oiled fretboard.
  6. Other guitars are fully painted wth thick lacquer. These seem pretty stable for tuning and relief. I usually just need to push then pull on the floating bridge on one of them and it is back in tune. I barely needed to touch the relief after a string gague change.

If your neck is super thin, maybe heavier strings wonā€™t flex as much and when the neck expands? This could cause more relief if the neck is expanding a lot.
Do you see any twisting happen with these relief changes? Iā€™d be watching for that in case you have one side of the neck moving more than another, or in case the tension of the heavy strings pull harder than the light and the neck doesnā€™t have the rigidity to stay untwisted.
Beyond that, I am out of ideas without having it to watch. Sure sounds like you will need to baby this one a bit more than others.

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Wow, didnā€™t think of all those!!!

My Strat neck is quarter sawn, I would guess all the others are similar. I canā€™t really know for any of them how the wood has been handled before the build.
Truss rod - very good point - my stable guitars are all single action but I donā€™t know about the Pacifica - itā€™s possible that itā€™s dual action.
Only one of my stable guitars (affinity tele) has a skunk stripe.

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Small side question, since my strat has a skunk stripe too: what is the function of this?

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Thatā€™s a good point. I havenā€™t looked for twisting in the neck as the relief changes. I should definitely check that. The neck moving more on one side than the other would not be good at all. Thanks for pointing this out.

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Yes, thatā€™s what I think, although now there have been quite a few other possible variables mentioned, especially by @mathsjunky that could also play a role and which I hadnā€™t considered.

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When constructing the neck the truss rod was traditionally put in a channel and covered with the fingerboard. When Fender created one piece maple necks (no fingerboard placed on top) then a channel was cut on the back of the neck and filled with a piece of walnut.
You will find these on guitars with fingerboards too if the channel was cut in the back of the neck.
If does however create a type of ā€˜laminateā€™ neck which I would expect would increase stability - no idea how much (if at all) though TBH.

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BTW, the reason I hang all the guitars on the wall rather than putting them in cases is that 1. I like looking at them, and fortunately my wife likes them as wall decorations, 2. When I look at them, I want to play them and itā€™s a big motivation for practicing regularly. In some ways, Iā€™m quite disciplined, but at the same time, Iā€™m a little bit lazy. Guitars in their cases are sort of ā€œout of site, out of mindā€ and I might be a bit lazy to get them out.

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If the fretboard on the Pacifica is thicker than the others, and the maple on the neck is thinner than the others, itā€™s possible we might have our culprit.

The thicker fretboard wood can exert more force and the thinner laquered neck is less able to resist the forces from the fretboard. I donā€™t think that the pieces would necessarily separate, as long as they were well-attached.

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Yes, a bit like a bi-metallic strip.

By the way, I think the truss rod in Pacificaā€™s is dual action.

Cheers,

Keith

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One way to test this might be to give the fretboard a good healthy rubdown with a suitable conditioning oil and then lower the humidity. An oiled rosewood board is going to resist moisture exchange far better than one that is dry.

Unless the fretboard is already well conditioned.

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