Martin 6% Moisture Content
 

The last few days just out of curiosity, I watched factory tours of Martin, Taylor and Gibson on YouTube. I think all of them were from Harmony Central. All were entertaining and enlightening. Out of the three, Gibson is the most hands-on, however I think it's a stretch to call any of these manufactured guitars "hand-made" :)

On the Martin tour, the tour guide explained that the wood comes in to the factory at about "40% Moisture Content", and then over a period extending at least one year they use a kiln and special room(s) to lower moisture content to 6% before they actually use the wood to construct guitars. He explained that 6% is basically as low as RH gets in the real world. The purpose, according to the tour guide, was to prevent the wood from cracking because of low humidity after the instruments are purchased.

This was interesting, and was not mentioned in either the Gibson or Taylor online tours. Does this mean Martin guitars don't really need humidification? There's a lot of real world connotations here, perhaps - This detail seems to mean that it is unnecessary to "anally" keep a Martin instrument at 45%↑↓ RH as you would need to do with a Gibby or Taylor.

No, they all build with dry wood and yes you have to keep your Martin humidified.

All wood gets dried to very low levels, I believe the minimum is 15%. Otherwise our houses would pull apart as the green wood dries and shrinks.

The value for the moisture content in the wood is not equal to the relative humidity value in the room.

hunter

Yeah, one of those Taylor videos I believe said 47% RH was what they used, and a balmy 75 degrees, I don't know what that translates to in wood moisture content.

Martin uses similar numbers:

They both recommend 45-55% ambient RH for their guitars.

Here is an article quoting both Martin and Taylor on their numbers:

http://americanmusicfurniture.com/humidity-matters/

That would be nice, wouldn't it? Unfortunately, it's not the case. My Martin SWDGT dreadnaught is super-sensitive to humidity swings (I'm talking three days at 30% and the top starts to ripple and sink), while my Taylor GS Mini never seems to change one bit despite being my throw-around, take-everywhere, camping-in-the-woods, leave-in-a-hot-car guitar.

Depending on species, 6% moisture content in wood is roughly in equilibrium with a relative humidity of 30% at 70°F.

One of our regular posters, "redir", recently posted a good explanation. The moisture held by the cells is cellular moisture, and this is likely the 6% that your are hearing. Relative humidity is absorbed and dispelled by the "spongy" fibres of the wood, rather than in and out of the cellular walls.

So, regardless of the RH of the air (to which the wood will reach equilibrium in relatively short amount of time), the cellular moisture content of the wood should be low before building. RH for building instruments is commonly near 40%, with some building in more or less humid environments depending upon the target market location.

So, basically, when we're talking about RH and moisture content of the wood we're talking about unrelated things.

Thanks all for your answers

Still related since room relative humidity does affect wood moisture content but not the same number.

Try this:

http://www.csgnetwork.com/emctablecalc.html

hunter

Think of it like this:

The moisture content of an object is the percentage of the mass (think weight for simplicity) of an object that is water. 6% of the wood's mass is water. RH is the percentage of the maximum amount of water that an air mass can hold at a certain temperature. Therefore, 100% RH is saturated. Any more water would precipitate out. 50% RH is 50% of the water it could hold before saturating at a specific temperature.