[pianotech] Bolduc glue

[Douglas Gregg]

Thanks everyone for your comments. I have been researching adhesives
quite extensively lately, ( I started with a term paper in chemistry
about 50 years ago) and am gathering manufacturers data for my
presentation in Seattle in July. I appreciate the specific comments
about Bolduc and I guess it will remain a mystery. For that reason, I
doubt I will include it in my presentation. If a manufacturer (or
distributor) won't supply any technical data on their product, I for
one, will not promote it. There is enough mystique going around
already as many of you have noted.

For what its worth, just about all of the adhesives that we would use
on pianos are thermoplastics except hide glue. I was following this
topic on a violin makers site. Even those guys, who are the purists of
the pure admit to using modern adhesives for some uses. The big issue
is whether the piece will ever have to be taken apart in the future.
If it might, then they use hot hide glue. It is not for the acoustic
properties which I think Delwin stated very well, it is so they can
get it apart later. Actually PVA glues are soluble in acetone and it
would be possible to break the bond even with these modern adhesives.
It may mess up the finish though.

For those concerned about creep, the addition of finely ground pecan
shells used in Better Bond adhesives for veneer work will prevent
creep. Hardness can also be achieved by adding silica (sand) as in the
West system hardener. However, West System data states that it will
actually weaken the bond slightly if used. Hardness is really
overrated. (Shore is a measure of hardness) Hardness means brittle. If
you have two pieces of wood expanding and contracting or being
impacted as in hammer shanks, brittle is not really what you would
want. Some slight flexibility will allow the bond to give a little and
not break.

Almost every adhesive we use is stronger than the wood we are gluing.
The most important part, as pointed out so well by several of you, is
not un-clamping the part too soon, particularly if the parts are under
stress. Most adhesives will have sufficient tack to hold in 30 minutes
but for maximum strength almost all manufacturers suggest at least 24
hours, in the fine print. For larger surfaces, double that, at least,
since most of them are water based and the water has to evaporate. The
larger the glued surface, the longer that will take.

Thank you all for your comments. I think this will be a lively session
in Seattle. I will present as much of the science as most of us can
tolerate so that you can interpret the manufacturer's data sheets and
make up your own mind.

Doug Gregg
Classic Piano Doc


Message: 1
Date: Fri, 24 Feb 2012 12:04:38 -0800
From: "Delwin D Fandrich" <del at fandrichpiano.com>
To: <pianotech at ptg.org>
Subject: Re: [pianotech] Bolduc glue
Message-ID: <010b01ccf32f$8a596a70$9f0c3f50$@fandrichpiano.com>
Content-Type: text/plain; charset="iso-8859-1"

It does creep. Given enough time, enough stress and/or enough heat--PVAs are
thermoplastics--all PVA adhesives will exhibit some creep. At question is
whether or not these things will exhibit enough creep in ways that will be
of any consequence to us as piano technicians and rebuilders. Years back I
used to worry about this stuff but then I actually started to think--I know,
unusual, but it does happen--about how we use adhesives in real life and
these days I don't waste a whole lot of worry time on them.

With very few exceptions glue joints in pianos are not subjected to high
sheer-stress loads. The most obvious exception might be the
rib-to-soundboard panel joint of a compression-crowned soundboard system.
Here, I would argue, age- and compression-related long-term creep--i.e.,
compression-set--within the soundboard panel itself is going to be a far
bigger concern than any relatively minor amount of creep that might be
taking place in the glue joint. And in some applications a bit of creep
might actually be to our advantage; a large cross-lapped joint, for example.

PVA adhesives are not approved for use in structural, load-bearing laminated
beams such as those used in some building designs (many churches, for
example) or for similar beams used in road bridges and railroad bridges. The
concern in building beams is not so much that they will creep over time but
what will happen to them in a fire. PVAs soften when exposed to heat and
it's not a good thing if structural beams fail while the fire department is
trying to put out the fire. Laminated structural beams used in road bridges
are subjected to heat from the summer sun, not to mention water from
periodic rains. PVAs are not generally recommended for use in bent-laminated
structures such as grand piano rims or vertically laminated bridges. Still,
CP Adhesives (http://www.cpadhesives.com/) lists CP-0200, a cross-linked PVA
adhesive similar to Titebond II, as one of their recommended adhesives for
curved laminations. And I have to confess--please don't tell the glue
police!--I've used Titebond II to glue up more than one vertically laminated
bridge body and, as far as I know, twenty and thirty years later they
haven't yet come apart or straightened out.

If I start building curved laminated structural beams for a railroad bridge
to be installed in Arkansas I'll probably consider using some other type of
adhesive. There are other adhesives that would better stand up to those
extremely hot and humid summer days. I also don't use PVAs for gluing up
grand rims. For one thing, the open-time for most PVAs is not long enough;
they start to skin over before the whole book of veneers could be assembled
and loaded into the press. But the shear stress on the glue joints in some
areas of the bent laminated rim are extremely high. I doubt this would be a
problem once the belly structure was fully assembled but until then I'd
think spring-back might be a problem. It would be an interesting experiment
and I might well be surprised. It wouldn't be the first time.

So, to your clavichord; as long as you don't put those parts you've glued up
with Titebond outside in the summer sun or the winter rain they should work
just fine.

Ron's point is well taken, though. It would be nice to have access to a lot
more information on the adhesives these companies are trying to sell to us.
You have to figure it exists somewhere. There is some information available
but you have to search for it. I've attached the product data sheets for
Titebond Original, Titebond II and Titebond III. (Does this list still
accept attachments?) Chapter 10 of the Wood Handbook is all about adhesives
and the bonding of wood. Either specific chapters or the whole book can be
downloaded (free) as a PDF file from
http://www.fpl.fs.fed.us/products/publications/several_pubs.php?grouping_id=
100&header_id=p

I may have some additional information somewhere. If I come up with anything
I'll add it to the list. But I don't think I've ever seen a Shore hardness
rating for any adhesive....

ddf



Delwin D Fandrich
Piano Design & Fabrication
6939 Foothill Court SW, Olympia, Washington 98512 USA
Phone? 360.515.0119 ? Cell  360.388.6525
del at fandrichpiano.com ? ddfandrich at gmail.com