Kiln dried vs Natural seasoning

[Delwin D Fandrich]

----- Original Message -----
From: "Tony Caught" <caute@optusnet.com.au>
To: <pianotech@ptg.org>
Sent: June 10, 2001 5:52 AM
Subject: Re: Kiln dried vs Natural seasoning


>
> ----- Original Message -----
> From: Richard Brekne <rbrekne@broadpark.no>
> To: <pianotech@ptg.org>
> Sent: Sunday, June 10, 2001 7:31 PM
> Subject: Kiln dried vs Natural seasoning
>
>
> Most if not all pianos built before 1910 (rough date) had soundboards that
> were seasoned timber.

Basicly true. Except that, when you think about it, all compression-crowned
soundboard panels have been kiln-dried to some extent.



> Both methods of crowning were used.
> In average climatic conditions one of those two types of crowning will
crack
> and come loose from the ribs easier than the other.
>
> In my opinion (saves flame suits) it is the soundboard that cracks that is
> not  under compression  and being freer to move (expand and contract) it
> loosens on the ribs and cracks.

Usually just the opposite. (Although at the time the crack develops there is
obviously no compression left inside the panel.) The wood fibers in the
compression-crowned panel are subjected to far more stress than are those in
the rib-crowned panel. That stress comes primarily in the form of
compression which results in a certain amount of compression set and the
accompanying loss of resiliency. All of this leaves the panel more prone to
cracking during dry climate periods. There is a bunch more on this in my
Journal soundboard articles.



> You have read most likely that the cracks are really expansion gaps and as
> such in my opinion, should not be filled with shims or with epoxy because
> this is then starting the compression of the soundboard, thus increasing
its
> deterioration rate.

This has also been my experience. Our prefered method of repair is epoxy.



> Groove the crack out so that the timbers do not touch, fill with a glue
that
> moves.  Colour the glue if you want but don't make it solid.

Most epoxies that are available to us--the general public--exhibit a certain
amount of cold-flow unless used in conjunction with a filler such as
colloidal silica, in which case they become nearly glass-hard. Used clear or
with just a coloring agent and a bit of wood flour the crack repair will
take on a bit of a hump during humid weather and develop just a slight
depression during dry weather. I've no idea just how long the epoxy will
keep on doing this, but its at least 25 years.

-- ddf