Varnish on Soundboards

[Barbara J. Fandrich]

----- Original Message -----
From: "David Love" <davidlovepianos@earthlink.net>
To: <pianotech@ptg.org>
Sent: Thursday, March 20, 2003 6:52 AM
Subject: Re: Varnish on Soundboards


> Mark:
>
> I recall the message(s) from Del and have read is recent posts and
articles
> on epoxy on soundboards.  One of the questions I have is how thick is too
> thick.  Joe G. addressed this somewhat in his post.  It suggests that a
> finish can be too thick and that a rubbery type finish applied too thick
> can reduce the function of the board.  The consensus on all post is that
> the ultimate finish should be very thin and should dry relatively hard.
> I've encountered a piano recently that has a very heavy coat of varnish on
> it, fairly recently applied (1 year or so ago).

Basically my point was that the specific coating material didn't matter as
long as it did not alter the stiffness and/or the mass of the soundboard
panel. Most, if not all, normal wood coating finishes do not.

Any finish material can be applied thick enough -- with multiple coats -- to
reach this level. I suspect that enough coats of varnish, especially
exterior varnish, could alter the damping properties of a soundboard panel
enough to affect the sustain and, possibly, the power output level of a
soundboard.



> The finish is still quite
> rubbery and flexes slightly to the touch.  I don't know if it is over
epoxy
> or not.  The sound of the board is strange, weak with poor sustain though
> the board is showing some crown and positive but not excessive bearing.  I
> did not hear the piano prior to the restringing so I don't have a way to
> compare but I am suspicious about the finish.  Part of my question is
> wondering if this piano might not have a problem due to the thickness and
> flexibility of the finish.   Though Del's research might have suggested
> that the types of finishes he applied within a relatively narrow range of
> thicknesses had no effect, that may not have been conclusive about how
> finishes improperly applied might not have a deleterious effect on
> soundboard performance.   He has talked about the importance of stiffness
> in a board, but if you get that stiffness by adding mass there you could
> create a problem.  If Del is reading this, perhaps he can comment.

All of the finishes tested were applied per the manufacturers directions.
Some required a single coat, sprayed on. Others required a sealer coat,
lightly sanded, followed by a finish coat. None had a film thickness greater
than a very few mils. All samples had the same material and approximately
the same film thickness on both sides.

The thickest finish in all of these samples was probably the varnish. This
had a brushed on sealer coat. This was allowed to dry for a week or so and
was then scuff-sanded. A final coat was brushed on. The seal coat was
thinned per the manufacturers suggestion--I don't remember how much--the
final coat was flowed on fairly heavily with a brush.

The whole idea with the epoxy coating technique is to add enough of the
right kind of material to deliberately affect both the mass and the
stiffness of the finished soundboard panel.

Del