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I'm ready to glue my 12 string bridge on & it occurred to me the top may be "too" dry We have a humidifier on our furnace buy as near as I can tell it is till 25 to 30 RH.

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Mike McNerney

I don't think that's too dry at all. I build around 35rh here in Ga and haven't seen any issues on anything thus far. Once you get to bridge gluing you're pretty much locked in anyway. The biggest factor RH will play (I THINK and please correct if I'm wrong) is as you glue bracing and close the box.

I wouldn't worry about it for gluing on the bridge. Honestly, I probably wouldn't worry about it for bracing or closing the box either.

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Steve Smith
"Music is what feelings sound like"

I don’t think it’ll be an issue either unless you take the guitar into a high humidity climate for a few months sometime. And then it’ll be more of an issue with the top swelling and separating the bridge glue joint. But I’m talking like above 85-90 percent like a tropical environment.

This winter when it got really cold for a few weeks I wasn’t watching the humidity in my house close enough ( 25% ) and a guitar I built last summer in about 50% now has a cracked top. Separated at the glue joint and actually cracked about 1/2 inch outside the joint as well. But also to my fault I had it hanging on a wall hanger which I guess is not recommended in low humidity. All other guitars in the same room don’t have any visible issues.

The difference between a top at 30% RH and 45% is a lot. You really need to put the bridge on at the same humidity level that you glued the top bracing at.

If you've built the whole thing at a low relative humidity then keep doing so.

You might want raise the humidity some before gluing on the bridge. Anywhere it rains you can have 90% humidity.

What was the Rh when you braced it? I'd get close to that when gluing the bridge.

if you have a braced top from 45% glue up 25% would pull it apart so I suspect you accuracy of the RH gauge if it was not calibrated

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

If you expect the guitar to see any high humidity for an extended period of time you may have a problem. The top (back too) will balloon up due to the high humidity, it's then possible for it to peel away at the bridge wings.
You'll probably be alright for short-ish periods of high humidity. You action should be the first indicator of when a potential structural problem might occur, hopefully giving you time to take corrective action.
Also, I'd second John's comment about humidity gauges, one that that's not calibrated is probably worse than not having one if you're trusting it to build by.

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Jim Watts
http://jameswattsguitars.com

Lots of good thoughts here and valid cautions. I'll add this is a 12 string with tons of string tension making the quality of the bridge joint even more important.

Also temp is going to be important for the quality of the bridge joint too in terms of glue curing properly.