[pianotech] CA Glue

[Susan Kline]

  Very interesting theorizing, Ron.

When I first noticed the effect, on a truly horrid hot day in California 
when I had to glue many weird wippens with narrow waists (breaking) on a 
tired upright, I theorized that the CA acted in some way as a catalyst 
to set up the white glue, but in the absence of a rationale for it, upon 
reading about CA glue and how it sets, I decided it was probably the 
other way around. But if what you say is correct, both may be true.

CA glue has something in it to keep it liquid in the bottle. Upon 
exposure to air, the humidity in the air ("a mono-molecular layer of 
water" was how the site described it) breaks this substance down so that 
the CA can crosslink. The crosslinking is the exothermic reaction. I 
learned from this same article (which I believe had been put on the web 
by a company which made CA) that CA bonds best in moist conditions, and 
it likes protein -- hence its gift for gluing people together. This also 
explains why it gets ivories so thoroughly stuck down, especially when 
one has cleaned the key crud off with a damp rag -- it likes the 
moisture, and it loves the traces of old hide glue. In fact, this bond 
for putting back on old ivories may be a little TOO good. If I remember 
right, Joe Garrett fumes about ivories put back on with CA, because they 
are the very devil to get back off again (should one wish to.)

It also prefers mildly alkaline conditions, and apparently white glue 
gives it this.

The reason that CA didn't work alone for me that first awful day (I had 
never used it previously, so I didn't know how) was that I put on too 
much. A big glob of it won't set up because the humidity in the air 
can't get into the blob to reach  the stuff which keeps it liquid in the 
bottle. This also accounts for how people in very dry climates think 
it's wildly over-rated. If they either used it with a water-based glue, 
or breathed on it, they'd get better results, especially if they 
realized they need to use only a thin layer, and that the water-thin CA 
doesn't fill gaps worth a damn.

Together, they seem to be a better gap-filler than either alone, because 
when they mix they get VERY EXCITED and sort of foam and froth, and the 
foam hardens. So, it seems like they try to expand on contact, and if 
one is pressing the pieces together, this may drive the glues 
(especially the thin CA) deeper into the surfaces. Also, white glue 
remains pliable, so it can accommodate some swelling and shrinking in 
the pieces glued, without pulling the joint apart, like a glue which 
sets up to be more brittle would.

Theories are all very well, but I wish somebody who knew their way 
around a laboratory would put in a few hours and figure out what is 
really happening.

Susan Kline




On 9/9/2010 8:51 PM, Ron Nossaman wrote:
>
> This "white" glue/CA thing has disturbed me since it was first 
> reported, as it seemed to be missing a sensible rationale for how it 
> worked. For whatever it might ultimately prove to be worth, or not, I 
> have a take on the water based/CA thing. Aliphatic resin (pva) glues 
> are largely RF curable. The RF dose heats the glue (microwave), and 
> accelerates the set. Heat supplied by another method ought to 
> rationally do something similar, in any world I want anything to do 
> with. Since the addition of moisture to CA glue triggers an exothermic 
> reaction from the CA, it looks to me that this produced heat is what 
> is accelerating the cure of the wood glue, and the CA has no other 
> realistic function than producing said heat. Bruce Clark (WNG) tells 
> me that the Franklin Assembly 65 glue that they sell is very 
> responsive to heat curing, which would make it an ideal candidate for 
> RF cured assembly processes. So... Being so heat cure friendly, it 
> might well be an ideal symbiote to CA as a quick cure PVA glue field 
> repair.
>
> Just a passing thought.
> Ron N
>
>