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 > >
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