Should I finish the inside of my acoustic?

[erikbojerik]

While fishing around for my pick, I discovered that the underside of the spruce top on my acoustic is not finished (at least it doesn't feel finished...). As I understand things, one of the reasons to finish the wood is so that it won't dry out (and crack, etc).

If I want to keep the spruce soundboard from drying out from the inside, shouldn't I apply some finish to the inside face? Or is spruce already "sappy" enough that it won't dry out? (but what about the inside face of the maple back?)

help me out here...

[Brian]

I've never seen a finish applied to the inside of an acoustic, seems like it would affect the tone a lot.

[JohnJohn]

I agree with Brian,all that extra weight on the soundboard.........

I think it was Selmer,(don't quote me ),had a line out with finished insides.Very flat and quiet sounding.

[VanKirk]

I would think it'd make it sound dull too. If the inside is drying out maybe you could pick up a humidifier. They're pretty cheap. All you do is keep a few drops of water in the humidifier and put that in the soundhole.

[Drak]

A lot of archtop builders do apply a finish to the interior.

But it's shellac, thinned a lot, brushed on, then lightly scuff-sanded back. It's such a light coat you wouldn't believe there is actually a finish on it, but 'just' enough to seal the pores.

When dealing with wood (finishing) there is a rule that whatever you do to one side, you do to the other side. So if you're finishing one side, you need to finish the other.

This is more for equal water/moisture absorbtion than anything else.

If you take a thick hunk of wood, could be 2" thick or even thicker, and you flat-sand one side and leave the other side rough-sawn and let it sit for a year or two, that wood will warp and cup due to irregular moisture absorbtion, one side (rough sawn) absorbing more moisture than the other side.

So a thin acoustic top would react, one side completely finished off and pretty impervious to moisture absorbtion, the other side wide-open.

True, acoustics are braced to help keep form, and those braces do help in that reguard, but one or two really thin brushed-on coats of thinned shellac will help a lot to keep both sides equal as far as water absorbtion is concerned, and not affect tone.

These thinned coats are usually called 'wash coats'.

[erikbojerik]

A lot of archtop builders do apply a finish to the interior.

This is more for equal water/moisture absorbtion than anything else.

Thanks much Drak; this is exactly what I was wondering.

All the more because it appears that I'll be getting into archtops in the not-too-distant future.