Also what is Balsa Cement? Again a brand name would be helpful. And why "pre-cementing"? And why with nail polish? Laquering wood before glueing sounds a lot like PAINTING wood before glueing which is supposed to be a no-no.
Balsa cement = model cement = household cement. It's some variety of plastic dissolved in some variety of solvent. Brand names are Ambroid, SIG-ment, Duco Cement, UHU-Hart, etc. Originally it was nitrocellulose/celluloid (plasticized nitrocellulose) dissolved in a mixture of solvents like MEK, acetone, butyl alchohol, etc. For most purposes, it's like really heavy nitrate dope Ambroid was one of, if not the, first of these. It was originally developed to adhere canvas to the bottom of wooden canoes, where it was painted on to first adhere the cloth, then waterproof it, with a brush. It is probably some variable type of easily soluble plastic like butyl acetate now.
It has some good and bad characteristics. It dries pretty fast, and sands pretty well. It is not very strong, and since it is viscous and dries so fast, it doesn't penetrate the wood very well, so you put a coat of glue on both surfaces, rub it in, let it sit for a few minutes, then apply more and assemble. It has almost no "grab" (unlike aliphatic resins like Titebond) so you have to hold or clamp the joint until it fully dries, which might be an hour or so. Traditionally, this was done with pins, which leave pinholes to later be filler, or requires complex arrangements of pins to hold the parts without actually going through the part.
If you need to remove it, more acetone or MEK will easily dissolve it and allow the joint to be remade. This same characteristic sometimes leads to the glue later bleeding through the dope, or at least discoloring it, particularly Ambroid, which is orange.
It also shrinks when drying just like all solvent-based products, which can pull poorly made joints together tightly, or, more likely, cause warps or dip in the surface above ribs and formers. The green box Nobler was notorious for developing slight dihedral when the glue holding the ribs to the D-tube spar shrinks, because all the slots were on the same side of the spar. The correct method is to alternate the slots top and bottom so that it shrinks the same amount on both sides. or put an additional "anti-warp" spar on the slot side.
It is very poor for laminating doublers, etc, because it will seal itself off and never dry. I have seen airplanes crashed where the nose split and the Ambroid in the middle of the doubler was still liquid many months later. Still, people got away with it for years, and very many stunt planes were built entirely model cement, including the engine mounts and doublers, and stayed together. Very long term, it's like any lacquer-type product, it continues to gas off for years and gets brittle to the point it can sometimes just turn to powder after decades.
The need to pre-glue also leads to one of the hallmark experiences of modeling - having it smeared and dried on your fingers and your pants, and later, chewing it off your fingers for the next few days. It's harder to chew off than Cyanoacrylate since it's reasonably flexible.
But the reason most people know and recall it with fondness is the smell. Building with Ambroid leaves a classic smell that evokes old-line hobby shops where outgassing tube of glue and people building model airplanes in the shop during work hours. The smell of Ambroid and balsa is what hobby shops are supposed to smell like.
Of course, when hippies came along, they discovered the sniffing/snorting glue (typically Ambroid since that was the most common) cause a long-duration very close exposure to the solvents that caused hallucinations and psychedelic trips. For a long time starting in the '70's some places kept it behind the counter and wouldn't sell it to kids to avoid abuse. Plastic model cement (Testors Cement for Plastic Models ) is very similar except that it contains polystyrene instead of celluloid or similar. For a while they added lemon scent or denatured it in some way to prevent abuse, with limited success, and removed the MEK, which made it work much less good.
Duco cement and several others I forget is also sold as "household cement" for general-purpose gluing. As far as I and my calibrated nose can tell, Duco and the current clear SIG-Ment might be exactly the same thing, which wouldn't surprise me at all given the unlikely possibility that SIG owns it's own chemical plant.
Most old-time modelers have fond memories of model cement like Ambroid. However, for almost any practical purpose it is obsolete. Cyanoacrylate, used correctly, is better in almost every way, requires no pins, doesn't shrink much, and is much, much stronger. Aliphatic resin (Titebond, etc) has a lot of "grab", is much easier since it doesn't require pre-gluing, sands reasonably well, has only moderate shrink (although it DOES) and works better for any air-drying application. Epoxy is stronger, cures in enclosed applications like doublers with no problem, shrink is undetectable, and is chemically nearly impervious to anything. The only thing model cement has over any other glue is sandability, but you can work around that pretty easily with good technique, and will still cause a problem with sanding if you get it on a flat surface.
I have a lifetime supply of Ambroid (no longer available) and SIG-Ment (still available for now, at least) and you can get Duco anywhere. For some jobs, I get it out and use i just to make the house smell correctly, and I always have a tube in my repair box that I take to contests.
Brett
Topic: New adhesives (Read 8370 times)