System Three Varnish

[gordon stelter]

--- Delwin D Fandrich <pianobuilders@olynet.com>
wrote:
> 
> OK. I bow to your far greater knowledge of chemistry
> and the history of
> varnish. I'm not a chemist--my response came from
> the answer to an inquiry I
> sent to one of the varnish-maker advertisers in
> WoodenBoat magazine some
> years back. But how do you reconcile all
> this with Jim Bryant's
> quote from Wilson Selby & Associates:
> 
> <<"ABOUT SPAR VARNISH........ (strictly our opinion)
> Spar Varnish has been used for years to provide a
> super-hard, weather and
> water resistant coating for exterior wood. However,
> this extreme hardness is
> not suitable for most exterior wood surfaces on a
> home.">>
> 
> Notice the reference to "super-hard." Not exactly a
> rubber sheet. And this
> tends to go along with my own experiences with
> modern "spar" varnish. Having
> once owned a large wooden boat I got lots and lots
> of experience with the
> stuff. Way more than I ever wanted. Sure seemed to
> dry hard. Could this be
> one of those descriptive names or terms that has
> changed with the times? Or
> is it now--the term--being misused by the
> manufacturers of the stuff?

You just hit it on the head, Del! The description from
Wilson Delby and Associates, in typical contemporeary
laxity regarding the King's English, seems to be
confusing "Hardness" with "Toughness" which are not at
all the same things, at least in the normal jargon of
the finishing industry!
    Hardness, of course, refers to the molecular
compaction of an element or compound. A diamond is
hard, although it's just carbon like soft graphite,
for this particular reason. This molecular compaction
allows the rapid transmission of shockwaves, i.e. 
vibration, which is what I think we want in a sound
board finish. At the thicknesses applied, the hardest
of finishes will stll have plenty of flexiblity and
not impede the soundboard much.  Of course, hardness
also means susceptibility to fracture along fault
lines, but this is not important in soundboards
because no responsible customer will be bouncing rocks
off it, anyway! Toughness, on the other hand, relies
on electrons in wide orbits, and susceptible to
exchange with neigboring atoms. It is essential for
elasticity, and why static electricty can be generated
by rubbing, well, rubber. You are actually rubbing the
electrons off. It is also this elasticity which makes
it absorb energy, i.e. vibrations, which is why we
don't want to use it, or anything like it, on
soundboards. But we do want to use it in high-abrasion
situations, such as  cabinet finishes (to some
degree--elasticity of course impedes one's ability to
"rub-out" a finish") and woodwork on boats. 
    Come to think of it, by these criteria I believe
that the ideal soundboard finish would be CA glue,
which might also be able to, essentally, create a
"chemically-laminated" soundboard crown----- but I'd
sure hate to work in that factory!


    Surely you will agreee that a rubber sheet
> glued
> > to a soundboard would be detrimental to
> conventionally
> > accepted notions of "good tone"?  And that UV
> > resistance is hardly a factor we need concern
> > ourselves with, as a soundboard put in that much
> > direct sunlight would disintegrate far faster than
> its
> > finish  would. ( And anyone who would treat a
> piano
> > like that would probably be tone deaf, anyway! )
> 
> While I have never tried coating a soundboard with a
> rubber sheet, I have
> directly compared a number of soundboard finishes
>  In no
> case were we able to attribute any tonal change to
> the soundboard finish
> until the coating thickness became a significant
> percentage of the overall
> thickness and/or the coating mass became a
> significant percentage of the
> overall soundboard assembly mass. That occurred with
> four of five coats of
> epoxy and with the polyester (I don't remember the
> coating thickness).
> 
> And, unfortunately, I have encountered altogether
> too many piano which have
> had their soundboards exposed to eiter direct or
> indirect sunlight during
> some part of the day. This being the case, and
> knowing how epoxy does break
> down fairly rapidly when exposed to UV light, I
> still recommend covering any
> coating epoxies applied to soundboards per my PT
> Journal article with
> another finish material containing UV blockers.
> 
> Del

Makes sense, Del, but I'd make this top coat as hard a
one ( not "tough" ) as I could find!

    Thank you for the discourse.
    Respectfully,
    Gordon
> 
> _______________________________________________
> pianotech list info:
https://www.moypiano.com/resources/#archives


__________________________________________________
Do you Yahoo!?
Yahoo! Tax Center - forms, calculators, tips, more
http://taxes.yahoo.com/