[pianotech] Bolduc glue

[Ron Nossaman]

On 2/24/2012 2:04 PM, Delwin D Fandrich wrote:
> 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.

Which is, of course, the point.


>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.

And I don't consider it a confession at all that I have built a number 
of curved laminated cutoff bars and vertically laminated horizontally 
capped bridges with Titebond original with similar disastrous results.


> 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.

Yes, I'd agree. If nothing else, You would be sitting around for a month 
waiting for the water to evaporate out of a 12x18" or bigger laminated 
beam before you could take it out of the press. Cycle time alone would 
be enough to discourage me, assuming I could get it assembled with wet 
glue in the first place.


>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.

Spring back is definitely a problem in those cutoff bars and bridges if 
they are pulled out of the caul too soon. Again, cycle time. I tend to 
turn the lights out on wet glue in the evening whenever I can, and in 
these cases I take all but a few strategic clamps off in the morning, 
and leave these on and the assembly in the caul for another day or two. 
Once adequately dry, spring back is nearly nonexistent.


> 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....

Me either, yet the mythology insists that one must have a glass hard 
glue for belly work, yet such a designation isn't quantified on any 
adhesive. Nor is a quantification for the dreaded creep. Sounds like 
just another typical piano specification doesn't it?
Ron N