water based finishing

[Delwin D Fandrich]

In the late 1980s I tested polyurethane finishes against nitrocellulose
lacquer finishes on soundboards. Panels coated with both finishes (including
the endgrain around the edges) expanded and contracted at about the same
rate. The panels coated with polyurethane may have been a bit slower to
respond, but not significantly so.

Neither forms an effective vapor barrier.

(Bear in mind the materials may have changed over the years since then.)

Del


----- Original Message -----
From: "Farrell" <mfarrel2@tampabay.rr.com>
To: <pianotech@ptg.org>
Sent: June 10, 2002 3:33 AM
Subject: Re: water based finishing


> I would dare speculate that if indeed wood was rotting under the finish,
that the wood was excessively moist when the finish was applied. Also, what
appears to be rot (were you able to actually check and see if the wood was
deteriorating due to fungal growth?) may have been evidence of moisture and
perhaps a less than perfect bond of the finish to the wood.
>
> Polyurethanes in general are not as "airtight" as some epoxies, and
coating epoxies are used in many applications for the primary reason to
limit the ability of water/moisture to penetrate through the finish. This
does not cause the wood to rot. Again, you might have problems with rot if
the wood was too moist to begin with. You can also have problems if the
barrier coat is breached, and water is able to soak into the wood from that
one spot (most often a problem if the wood is in direct contact with
water) - the wood could start to rot in this case because it is let in, but
not able to escape easily.
>
> I don't think the characteristics of any finish alone will cause properly
prepared wood to rot. Please correct me if I am wrong.
>
> Terry Farrell
>
> ----- Original Message -----
> From: "D.L. Bullock" <dlbullock@att.net>
> To: "Pianotech@Ptg. Org" <pianotech@ptg.org>
> Sent: Monday, June 10, 2002 1:45 AM
> Subject: Re: water based finishing
>
>
> > I was talking about regular pianos finished with polyurethane varnish.
They
> > were not outdoors. the gray streaks were the rotting wood and not in the
> > finish.
> >
> > DLB
> >
> > >writes:
> > >> I know the problem with Polyurethane Varnishes is they are so
airtight
> > >they rot
> > >> the wood underneath with gray streaks showing after 5-10 years.
> > >
> > >Hi D.L. -
> > >
> > >I am not familiar with this phenomenon.
> > >Is this on wood that is outdoors?
> > >Are the grey streaks in the wood or in the finish?
> > >Can you elaborate?
> > >
> > >Curious...
> > >
> > >Mark Potter
> > >bases-loaded@juno.com
> >
>