I always used to buy epoxy locally in disposable dispensers that are supposed to dispense equal ratios of the components. The dispensers never work that well: one side always starts to move first and then to get a reasonably equal mix I have to mix up a lot more than I need.
The 3M duo-pack adhesives are sold separately from the dispenser. Because the dispenser is not disposable, it can be a decently built tool, like a caulk gun for epoxy.
The way it works is that you slip on the adhesive cartridge. The applicator has a plunger that pushes up the adhesive cartridge. Think caulk gun. The epoxy comes in double tubes like a doubled tube of caulk. When an adhesive has a different mixing ratio the tubes in the cartridge have different diameters. And there is a different plunger that fits in the tube. The supported mixing ratios are 1:1, 1:2 and 1:10 because those are the ratios of adhesives available. When you buy the system you get the first two plungers, but the 1:10 plunger is sold separately as it is used only for DP-8005 and DP-8010, I think. Just like a caulk gun you can, but you need not remove the adhesive cartridge between uses. The gun stays clean. There is no need to clean it. (Unlike a caulk gun, the adhesive doesn’t leak out the back and get on the gun.)
In fact, if you’re not so worried about waste there’s even a further convenience: static mixing nozzles. These nozzles attach to the end of the epoxy tube and do all the mixing for you so that it really works like a caulk gun: what comes out is ready to use, completely mixed epoxy.
But even if you don’t use the somewhat wasteful mixing nozzles you can still use the gun to extrude the correct ratio mix of 3M adhesive products and then hand mix. I have been able to mix up just the amount of epoxy I need when with the old system I would have mixed ten times what I needed. (No exaggeration here.)
I first got this system because I was trying to glue zinc-plated magnets to polyethylene. I tried regular epoxy. It doesn’t stick well to either one of these materials. There are two adhesives that I think are of particular note in the 3M lineup.
The DP-190 (which I have only used a tiny bit) is supposed to stick to everything except the “low surface energy” plastics. I saw that it is recommended for use with the zinc-plated rare earth magnets (by the magnet sellers). The DP-8005 is designed to stick to low surface energy plastics. I got it for my application.
I also got a small mat made out of teflon because nothing is supposed to stick to that. This was great for repairs using epoxy. I repaired something and laid it on the teflon and it peeled right off after it was cured.
According to 3M, epoxy shelf life is less than a couple years, so you don’t want to buy a lifetime supply at any given time. The shelf life of DP-8005 is only 6 months. The shelf life of the previously reviewed Scotch-Weld Two Part Urethane is 1 year.