Formaldehyde glue

[Farrell]

----- Original Message -----
From: "Kenneth Zahringer" <zahrprice@earthlink.net>
To: "Members of" <pianotech@ptg.org>
Sent: Sunday, October 29, 2000 8:48 PM
Subject: Formaldehyde glue


> I was recently called to check out a piano that another technician had
> declared untuneable.  Well, he was right.  The pinblock had completely
> separated from the back beam - end to end, top to bottom.  I looked in
> the gap and both surfaces were covered with what looked like a flocking
> of glue.  I scraped some of the glue from the underside of the block, in
> back, and it crumbled in my fingers - full of air bubbles, I think.
> Once it crumbled, though, the remaining granules were rock hard.  The
> manufacturer said at the time this piano was built they were using
> formaldehyde glue in this joint.  The warranty expired some years ago,
> so it's up to the owner and me to fix it.  I would like to do this
> without disassembling it, replacing the block, and restringing it.  It's
> not that old and the pins are still fairly tight.
>
> My problem is that old glue.  I know there is no way I could clean all,
> or even most, of it out of a gap that's barely 1/4 inch wide.

I agree that it would be hard to get all or most of the stuff out. That
rules out repair with a glue that requires good mating surfaces, like
Titebond or hide glue, etc.

> And the
> granule are so hard I'm sure they would prevent the two surfaces from
> being clamped together effectively.

Well, you are likely right that they will not go completely back together,
but I should think they can be drawn together close enough. I would just do
the standard approach. Scrape anything that is loose and vacuum with a
POWERFUL vacuum. That will remove the real loose stuff. FORCE West System
epoxy down into the crack with an appropriate thickness stick to push it
down there (COMPLETELY fill the crack). You must be the judge on how thick
to make the epoxy. Maybe observe a test area near the top. I usually use a
pretty thick (thickened with their hi-density adhesive filler) mixture, but
you may want something thinner to be sure the epoxy saturates the crumbly
glue to the wood. Clamp and draw together, through-bolt. Even with lots of
yucky looking crumbly glue in there, I would expect a 90% chance of complete
sucess - one as good as any pinblock separation repair.

> Does anyone know of a way to soften
> or dissolve formaldehyde glue?  Can it be "reactivated"?  If it were
> softened or partly liquefied, would it interfere chemically with other
> glue, like Titebond?  Based on what little I know about formaldehyde
> glue, I'm not sure I want to use it in my shop.

I don't know anything about it.

> Ken Zahringer, RPT
> Columbia, MO
>


Terry Farrell
Piano Tuning & Service
Tampa, Florida
mfarrel2@tampabay.rr.com