We usually have nice warm, sunny summers in Nova Scotia, but this year it’s been about 6 weeks of either rain or unrelenting high humidity, and my Martin GPC X2 is definitely not playing as well as during the previous 2 summers I’ve owned it.

The action keeps getting higher. I checked the neck relief, and the neck is straight - no relief.

I believe the I have traced the problem to “belly bulge” - the top is bowing upward behind the bridge…lifting the bridge and raising the action.

I measured the gap between the ruler and the end of the guitar, and it is 1/4". This seems excessive to me, but I’ve never measured it before.

I have a theory…

The GPC X2 is among the least expensive Martins. It has a solid spruce top, but to reduce costs, the body is made of High Pressure Laminate - essentially plastic.

I believe the wood top is absorbing moisture and expanding, while the plastic body is not. This unequal expansion means that the top has to bow upwards to compensate.

My girlfriend has a cheaper Denver guitar - made with laminated wood top and body. Her guitar does not seem to be suffering in the same way.

My questions:

  1. Is this a reasonable theory? Or are there other reasons why the top may be bowing?

  2. What’s the best cure? In another thread on humidifying, @stitch has suggested desiccant packs. I don’t have a hard case, so am considering putting the guitar in a large, sealed plastic bag with the desiccant packs when I’m not playing it. Is this a good approach?

  3. This problem took weeks to develop, and may take weeks to fix. Is there any way to - safely - accelerate the process?

All Laminated guitars are affected a lot less than solid wood. Yours being both would suffer the same as an all wood one.

Yes this could be the problem but also if any of the braces have become unglued the top could bow. Yours isn’t to bad. Flat top guitar aren’t actually flat they have a slightly curved top. So I’m thinking it’s just a little over hydrated.

I’ve here of people having summer and winter saddles that they change with the seasonal changes. For now I’d try the Humidity packs Mari posted the one’s she is using on her new Martin and putting the guitar and soft case in a plastic bag to see if that helps.

It could take longer to go back because wood loses moisture slower than it absorbs it. You could have a Luthier check it out and make you a lower saddle so it easier to play.


Interestingly and kinda creepy too… This youtube notification came up while I was reading these posts here…

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Or you could use holistic approach and keep the whole room, it it is not to big and not so open properly humidified by room humidifier and separated humidity meter. I play in a small bedroom, keep the guitars there too, using scheduled on/off periods I can keep it between 45-55% whole year.

Is this important for guitars :guitar:?

Only if you live in an environment when it is very humid for a large part of the year, and you have no air conditioning.

And then really only for acoustic guitars.



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@Majik :smiley:

I took my guitar into the L&M luthier, and he confirmed that the guitar is over hydrated.

But according to him, it is the neck that is the main problem. When sighting from the headstock, the fretboard should line up with the top of the bridge, but it is well below that.

So I bought a D’Adderio hygrometer, and measured the levels in my apartment. They’ve been between 70 - 80% the last couple days. It’s been warm and sunny (finally!), so I assume they were quite a bit higher earlier in the month during the rain.

Luthier gave me some desiccant packs they had lying around from gear packaging, and I revived them by heating in the oven at 250 F for 2 hours. Stuck them in a sock, and am hanging it in the sound hole when not playing the instrument.

But I’m thinking it will take all summer to recover, unless I take more direct action.

Considering two options:

  1. Getting a lot more desiccant (apparently crystal cat litter is the way to go), and storing the guitar in a plastic bag with some big packs.

  2. The cubby under the stairs has an electric water heater, and the humidity is about 10% lower there. And I’ve been able to drop it another 10% by putting a small forced air heater in there…though this raises the temp to 30 C, which might be a concern.

Now it’s July, 2024…so following up from last year…

This was indeed a viable solution. It took about a month of storing the guitar in the bag when I wasn’t playing it, but the action came down noticeably (about 1/8", according to my rough measurements with a vernier caliper).

1/8" doesn’t seem like a lot, but it made the guitar playable again, especially on the higher frets. I eventually bought a Dunlop string height gauge, and measured 0.080’ at 12th fret. Only $15 on Amazon, and so much easier and more accurate than the vernier caliper!

Now it’s summer again…and the action is going up again. 30 C today, measuring 87% humidity at the sound hole… 64% when the guitar is in the bag.

I’m experimenting with “Damp Trap” closet dehumidifiers, available from my local Dollar store for $1.50 each. Looking like they may be a cheaper and tidier option than the crystal cat litter, but it’s too soon to tell.

Hi Tom!
In my opinion, apart from your guitar, you should also be concerned about your own health too. Ideal relative humidity for humans is between 40% and 60%.
80% RH in your flat is definitely something you need to start thinking how to address.

Interesting point.

I know mold is a potential issue, but my place is well ventilated, and does not smell musty, so I’m ok on that front, I think.

Are there other potential health issues when RH goes above 60%?

Good ventilation is always a good thing!
There are some plots like this
But I haven’t read everything on the subject.

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I live in the upper Midwest of the USA (Minnesota.) Our summers can be quite humid, so I run an electric dehumidifier in the room where the guitars are.

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I think I’ve had one cold in the 3+ years I’ve been living here, and no symptoms of anything on this list, so I’m not too worried about it.

But I’ll keep an eye out for any changes in my general health.

Have some experience with electric dehumidifiers, but that was 10+ years ago. Those units were expensive to run, and not very effective, but maybe they’ve improved?

What brand do you have, and would you buy it again?

If it has to run a lot it can make the room warm, but it takes a lot of water out of the air. I have to empty it 2-3 times a day at the peak of humidity. It’s a Danby, and I would have no problem getting another one. I’ve had this one a long time; they’re probably more energy-efficient now.

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