For those who are wondering, "double cementing" is a technique to use with model cement to get better adhesion, mostly due to improving the otherwise poor joint penetration, particularly with Duco/SIG-Ment/UHU, which are fairly thick and quick drying. The idea is to smear glue on both sides of the joint/interface, let it mostly dry, then glue it again and assembled the joint. As noted, this does allow it to "stick" to some degree, but you cannot count on the "grab" of the glue holding it in place, any residual force will allow it to creep away over the first 30 minutes or so. So, double-glue or not, you have to hold all the parts rigidly together for the entire drying time. If it does creep, the joint strength will be extremely poor. It also takes longer to dry than you might think, it is probably not rigid for maybe 2 hours even at sea level, 90 degrees, and 20% humidity, and much longer if it is more humid.
Note that the "fast drying" types are actually worse, it will thicken up and penetrate even less good than the regular drying types, and need pre-gluing even more. Ambroid is pretty thin to begin with, it penetrates better than the others, having originally been intended to be used like dope rather than wood adhesive (long before anyone had discovered balsa wood for models). It also has much lower solid content, so it is not as strong in the sense the glue itself is hard or rigid, although the joints generally work out better.
I have seen references to double cementing in old books dating to the late 20's, so neither Tim nor I invented it. The same book told you could make your own glue by dissolving celluloid toothbrush handles in acetone, forming a cheap alternative to "Amber-oid" model cement. Toothbrushes haven't been made of celluloid since about the 40s, but I have successfully dissolved one of the orange translucent cheapie toothbrushes in lacquer thinner and gotten something like it. Then I used Hot Stuff to actually build with.
Aliphatic or PVA glue, on the other hand, "grabs" so once you get it aligned and pinned/clamped, it will not creep after about the first minute or so, and the penetration (being water-based) is much better, and you should probably *not* double-glue it, or at least if you do, don't let it dry for more than a minute or two, because it wants to be liquid everywhere. Double-coating it only helps by letting it penetrate the wood better, but it's good enough for our purposes without special techniques.
Brett
Topic: Cellulose glue? (Read 10108 times)