Soundboard finishing material - what and why?

[Farrell]

>>Is the expectation that the finish will reduce the
>> seasonal moisture exchange?
>
> The main port of entry for moisture is the end grain.
> That's the area you want to seal really well, and
> fortunately coat thickness isn't important for tone
> there.  I would guess that coating the radiating
> surface with lacquer has mostly a cosmetic effect.

I couldn't find a reference for addressing this, but I suspect the panel 
surface also accounts for much of the moisture transfer occurring in a 
soundboard. Yes, you are correct to imply that the end grain much more 
readily will facilitate the transfer of water, but even if it does so at ten 
times the rate of the quarter-sawn face, in the time it took for water to 
migrate 1-1/2 inches into the end grain, water would move completely through 
the panel through the quarter-sawn face. I guess we'd have to find an 
authoritative reference to be sure exactly what the capacities of moisture 
transfer are. But even if the two surfaces differed by a factor of 100, 
water would migrate into the center of the panel through the flat surface 
before it moved a foot from the end grain.

> Just a week ago, I did an experiment and soaked the
> surface of an undamaged piece of wood with a very
> light "highly" penetrating epoxy while avoiding the
> end-grain.  I wanted to see if it has any chance of
> getting into undmaged wood.  Nothing got in.

Nothing got it where? The epoxy didn't penetrate into the wood? For what 
duration was the epoxy "light 'highly' penetrating"? What kind of wood? How 
did you determine epoxy penetration?

Terry Farrell

> Vladan