sealing inside the bass

**Matthew Tucker** · #1 10-11-2005, 12:18 AM

I've been thinking about timber shrinkage.

I'm interested to know why wood inside a bass is not sealed in some way. Would not a thin layer of, say, shellac on the inside of the table, back and sides, reduce or slow the effect of humidity on the instrument?

In the same vein, why are cross braces for flat backs made of spruce, as opposed to maple - which would have (I would have thought) a similar shrinkage rate to the back itself, thus reducing tendency to crack?

Silversorcerer · #2 10-11-2005, 01:04 AM

Certainly an interior sealant would inhibit both drying and soaking up moisture. I think sometimes linen or other cloth is used to line the ribs. I don't know how much that slows down moisture. Sealing the wood up totally might impede the opening up of the wood to sound.

On the back cross braces: even if you used maple the grains will be running perpendicular resulting in very different expansion and contraction rates. A type of wood has an expansion rate along the grain and a different one across the grain. I don't know why spruce is used.

arnoldschnitzer · #3 10-11-2005, 06:41 AM

Actually, some makers do seal the insides of their instruments. Seems like a good idea until the bass cracks and you want to attach a cleat or a linen strip. No go. Also, the basses I've seen that are sealed up inside seem to crack MORE than unsealed ones (this could be a coincidence since the basses I'm thinking about are built very stiffly). Keep in mind that humidity finds its way into and out of all porous objects, finished or not. Spruce is used for crossbars because it is light, strong, and springy.

Eric Rene Roy · #4 10-11-2005, 12:15 PM

This discussion is similar with wooden boat builders. Some say don't seal the inside of the boat as it allows the wood to breath and do what it wants to do natually. Others say seal the inside just the same as the outside to completely lock out (and in) any mositure.

Obviously basses are not boats, but I think you will find similarities between the two, and if you ask a room full of luthiers and a room full of boat builders to seal or not to seal, you will get varried answers and some pretty heated discussions!

drurb · #5 10-11-2005, 06:28 PM

Quote:

Originally Posted by eroy

This discussion is similar with wooden boat builders. Some say don't seal the inside of the boat as it allows the wood to breath and do what it wants to do natually. Others say seal the inside just the same as the outside to completely lock out (and in) any mositure.

Obviously basses are not boats, but I think you will find similarities between the two, and if you ask a room full of luthiers and a room full of boat builders to seal or not to seal, you will get varried answers and some pretty heated discussions!

Eric-- what a great idea! We can buy a bunch of CCB's on Ebay, attach small masts to their bridges, throw on a bedsheet and set sail! Let's set up the first TB bass-boat races.