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All you have to do is to View Active Topics, and look at the new post about a cracked top. There's your proof that humidity matters. Most of the repairs that come into my shop, are from humidity damage. Wood is a wonderful barometer. It reacts almost immediately to humidity changes.

Do I keep my shop at 45%? Yes.

Do you have to? It depends. If you're going to consistently build guitars, or collect them, then you should have a room with controlled humidity. Why 45%? Because, it gives you wiggle room for a guitar that faces low winter humidity. Open cracks can be tough to fix and loose braces tough to get to inside of a guitar. My shop swings between 45-50%.

If you can't control the ambient humidity, it's pretty easy to control a room or closet. For a single build, in between clamping, just store the components in a case or box with a humidity control bag, like those made by Boniva or Daddario. They make humidipaks for 45-50% humidity.

They're on Amazon.

I had a Masterworks Tree of Life MD95 Alvarez with solid EIR and engelmann. I had no problems with humidity changes at all, for years, until I did.

I found 2 cracks in the grainline of the EIR back. That was my very first guitar repair.

why does the RH cause so much of an issue?
woods will swell when wet and shrink as they dry out. Plates without the braces usually just cup and flatten. So once the braces are on you lock the top. The top can move as much as a 1/4 in in humidity changes.

so if you manage RH to within a +/- 15% you are pretty safe. So at 50% build you are safe 35% to 65% this is where I find perfect for my area. I have made guitars for Arizona and humidity there is pretty low so I did build at 40% this helps for that area.
Consider where the guitar is headed that is why I use 45% most areas will be in the 35% to 60% . As RH rises from your build humidity the top rises. The end result there is high action as it dries down the action drops and the top shrinks and it is all about how the braces let the top pull and push.
as it dries the top shrinks and the stresses build to the point where it will pull a crack right into the top.
So take this into consideration when you brace the top and back

OP lives in San Jose, his shop is in San Jose, the guitars will stay in San Jose, where OP says RH is stable and not subject to the great swings most of the country sees. Conversations about varying RH are irrelevant to that person in that place.

phavriluk wrote:OP lives in San Jose, his shop is in San Jose, the guitars will stay in San Jose, where OP says RH is stable and not subject to the great swings most of the country sees. Conversations about varying RH are irrelevant to that person in that place.

He asked a question and it was answered. BTW, the RH in San Jose, CA, is currently 79% which is detrimental to guitars. The RH may average a certain level. It certainly doesn't mean that it doesn't swing to extremes.

Nothing is irrelevant in this forum.

We have numerous people with questions, who read these threads. They don't all ask questions. Some are shy about asking questions.

In this forum, we like to explain why we do the things we do. Anyone reading can either use the information, or disregard it. Nobody is forced to read the threads. What is irrelevant to one person, is usable info to another.

Diane Kauffmds wrote:....
If you can't control the ambient humidity, it's pretty easy to control a room or closet. For a single build, in between clamping, just store the components in a case or box with a humidity control bag, like those made by Boniva or Daddario. They make humidipaks for 45-50% humidity.
....

That's a great idea! I'm already discovering I can keep my garage pretty stable, and with a dehumidifier I should be good, but your suggestion is great for someone trying to deal with large swings without investing lots of money.

BTW - I'm finding that despite the outside humidity being high in my area, my garage stays much closer to 50%....maybe because the gas furnace is in the garage? Hopefully with the dehumidifier I can keep it pretty close to 45%.

I should also note that I've had fine wood instruments in my house for ~25 years now and never had any problems with cracks, warping, etc. I typically keep my acoustics in their cases (some of my electrics do sit out full time), and I'm guessing the humidity inside the house stays much more consistent. Most of the gigs I play are indoors, and the outdoor ones are only in the summer, so at least in my experience, factory built guitars do just fine in San Jose without special attention. I can only assume the big names keep their factories around 45%....so I'm going to try to do the same.

Keeping the acoustics in cases is the ticket. Your doing a good job.

Well my dehumidifier arrived...instructions say it has to sit for 24 hours before plugging it in. So tomorrow (Wed) I'll turn it on and hopefully by Thursday (Thanksgiving) my humidity will be close to 45% and stable. It has been in the low 50's in my shop the past few days with not much deviation, so I'm hopeful the wood will equalize to the 45% RH air pretty quickly and I can start gluing soon...been a long wait.

Mark Scrivener wrote:Well my dehumidifier arrived...instructions say it has to sit for 24 hours before plugging it in. So tomorrow (Wed) I'll turn it on and hopefully by Thursday (Thanksgiving) my humidity will be close to 45% and stable. It has been in the low 50's in my shop the past few days with not much deviation, so I'm hopeful the wood will equalize to the 45% RH air pretty quickly and I can start gluing soon...been a long wait.

My husband spent 60 years in HVAC (heating, ventilation, & air conditioning). He's worked on everything from massive industrial centrifugals, to home ac systems, even marine research machinery. He was one of the first people to get a universal license for handling refrigerants with fluoro hydrocarbons, when the EPA started licensing.

I recently replaced my dehumidifier with a larger model and I asked him about the oil in the compressor and whether to allow it to settle after shipment, because mine didn't instruct on whether to allow it to sit.

He said that these units have very small compressors. Unless it's been upside down for days, not to worry about oil in the lines. So naturally, I didn't listen to him and I allowed mine to sit overnight too, just in case. Hahaha!

You'll be fine tomorrow to start it up. Just remember, it's not just the wood. Everything in the room, walls, floor, ceiling, etc. have to dry out. You're already at 50%, so i imagine you'll probably see it happen quickly. But if it takes a bit longer, it's not a unit defect. A lot depends on the cubic footage of your space vs unit size.

You're lucky that you live in an area with stable humidity. I live in West Virginia, where we can go from 90% humidity, and with the winds coming over the mountains, dry out to 40% in a couple of hours. The lowest I've seen is 9% (that's no typo).

I have one build which will head to Indianapolis, IN and another heading to Riverside, CA. So, like John, I prefer to glue with my shop a little on the dryer side.

Thanks Diane! Well I turned on the dehumidifier this morning and it has been running all day...outside is 73% RH....My garage workshop has gone from 54% this morning to 48% at the moment with the dehumidifier running non stop. Hasn't pulled a ton of water out yet, just a few cups, but at least things are moving in the right direction. Outside humidity is supposed to drop down around 40% for the next few days, so we will see what happens in the garage. Holding off on gluing until I know how the garage is going to track with outside changes...but can't wait to get started!

Sounds great. Keep us informed.