Tuesday, January 08, 2008


It's been raining a bit recently here in Southern California. Needless to say that humidity have gone up, which is something that is close to lethal when you glue braces on your soundboard.

I have a two hygrometers, one that sits in a clock I have on the wall in the garage/shop, and a little digital cigarbox one I bought a while back for our piano. I while ago I took the little one out to the shop only to find that they were not displaying the same value at any given time. When the digital one showed 38% the analogue one in the clock read 58%. I couldn't believe that they are so far apart.

Two weeks ago I took my little digital hygrometer with me to my local wood and tool shop Rockler, who sells analogue hygrometers for clock makers. I wandered about in the shop until mine had settle and compared it to the ones they had on display. They all consistently read about 9% higher than mine. When I got home I adjust my shop hygrometer down about 10% and have used that as my reference, and now it is at least fairly consistent with the local weather forecast. I'm still not sure how precise it is and I might try and go to one of our local museum and compare it to one of their hygrometers. They should be quite accurate.

But to deal with the damp weather conditions, I choose to try out a trick from Bruce Hoadley's book "Understanding Wood". He suggests wrapping your wood in plastic until humidity is back to normal.

I'm in the middle of bracing the soundboard and hope to avoid to many unpleasant surprises.
Ideally you want to get the soundboard braced and glued on to the body in a close to ideal humidity conditions as possible, otherwise you will be in for some nasty surprised later on.

A fellow builder from LuthierForum just posted several pictures of what looked like someone had stuck a hose to the soundhole and sucked out all the air from the guitar. It was not a pretty sight. Basically he had been building in too humid condition and when the guitar settled in the drier indoor winter air, the thin soundboard and back had contracted and caved in showing all the braces that were still trying to hold these plates in place.

Nasty business!!


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