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Ask Bob: Should I re-wet a humidifier while it is still wet?

Question: Regarding humidification it has been suggesting that one should not re-wet a humidifier while it is still wet. Can you please explain the reasoning? We live in an area that is extremely cold and dry in winter, and keep our guitars in cases with soundhole humidifiers damp at all times. We have also been advised by a local guitar technician that leaving a dry, spongetype humidifier in a guitar actually can cause additional drying by virtue of the sponge absorbing humidity/moisture from the guitar.
Andy Spindler Calgary,

Answer: You bet I can explain. A dry sponge indicates that the guitar has taken all the water and wants more. A wet sponge indicates the guitar is still absorbing water. If you re-wet when it is already wet, you may just raise the relative humidity higher than is good for the guitar and begin to force feed it too much water. The simple cycle of letting the sponge go dry will always tell you that you’re not giving it too much. If the sponge goes dry often, simply keep re-wetting it. A supple sponge that isn’t really wet but also isn’t really dry indicates nearly the perfect relative humidity, so don’t re-wet that sponge until it’s dry. And remember, this whole exercise should take place inside a closed guitar case.

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