Fixing a sinking top with humidifier?

[soma89]

Hello,
I have a Martin 1965 d-12-20 12 string acoustic that is sinking near the soundhole. What can i do to fix it? Would buying a soundhole humidifier help to lift that part of the body up a bit?

Any suggestions?

[stanron]

You can get that type of sinking that is accompanied by belly bulge on the other side if the bridge. This can indicate some kind of failure in the X bracing and bridge plate area. If you can get light and a mirror or camera inside you could check for broken or detached braces.

[Corky Long]

Humidifiers won't undo 45 years of the tension that a 12 string puts on the top of a guitar. Lots of tension.

Put a straightedge on the top to see how much the top is bulging below the bridge. Other poster's recommendation is a good one, too.

You should keep the guitar humidified too, of course, but that won't do much for this issue.

Is it playable? What's the action like?

[gitnoob]

Originally Posted by Corky Long

Humidifiers won't undo 45 years of the tension that a 12 string puts on the top of a guitar. Lots of tension.

+1. What you're seeing is a deformation of the top due to string tension, not a humidity issue.

The standard treatment is to replace the bridge plate, which is probably warped. A flatter bridge plate will help flatten the belly.

Martin never put very beefy sound hole reinforcement in their guitars, so replacing the sound hole reinforcement could also help.

Finally, trying to flatten the top with heat and cauls could help.

Frankly, this is one reason why buying "vintage" guitars isn't such a hot idea.

[soma89]

Let me also say that it has had its rosewood bridge shaven down to lower the action. It`s currently in for a new bridge installation and neck reset..would this work improve the sinking body at all?

[gitnoob]

No, the body will still be deformed, but the action should be improved.

In all likelihood, the reason you need the neck reset is due to the body deformation (nothing to do with the neck per se).