Guitar Making Tip Number 67 is about wood. Wood is hydroscopic, which means that it take in and lets out moisture as the environment changes. This needs to be controlled in the build to be stable. Here is what you need to know.
Wood is a Hydroscopic Material
Wood is a natural material, and it has the ability to change with the environment. As conditions get more or less humid, the wood absorbs and releases moisture. This is all part of nature, but the problem is not in the moisture, it’s in the size.
Wood changes size when it absorbs and releases moisture. As a piece takes on moisture, it gets larger, When it lets out the moisture, it gets smaller. This change in size is what you need to control.
If you glue a couple boards together, and then place them in an area of high humidity, the boards will swell. When this happens, it puts a lot of stress on the glue joint between them. Over time, the pressure and the stress weaken the area, and the joint can fail. Here is what you can do to prevent this from happening…
Working in a Controlled Area
When you are making your guitars, work in an area that has an average humidity for where the guitar is going to live. For example, if you are expecting that the guitar be in a place with central air conditioning, you can expect a lower humidity level.
Houses with air conditioning are lower in humidity, and have a more even temperature than other places that use different cooling methods. You can benefit from building the guitar in the same type of environment, because the difference in humidity will be minimal. This means less stress on the guitar.
The important thing to think about is the stress on the joints of the guitar. If you can build in an area that is similar in temperature and humidity as the final living space of your guitar, you will end up putting less stress on your instrument.
Using a Good Finish
Finishing wood is the best way to slow down the effects of humidity changes. When you apply a finish, you add a layer over the wood. This layer helps slow down the passing through of humidity and moisture.
Most guitars are finished with lacquer. This is a great finish, and it will help you prevent popping any joints due to humidity. Apply the finish according to the manufacturer, and you will end up with a nice seal.
You may also entertain finishing inside the guitar. This is done many times with a different product like a shellac, and it brings out the beauty of the inside of the guitar as it protects from moisture gain/loss in that area.
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