Hey Ducksterman,
I use a thin mix of regular head cement on most FW stuff, but for SW flies I use Sally Hansen Hard as Nails and Devcon 5-Minute Epoxy depending on the fly pattern. I use SH on some intermediate steps in tying FW nymphs and SW flies to lock in materials for added durability and let dry overnight before finishing.
In salt, Deceivers, Clousers, Flatwings and Hollow Flies and stuff like that get SH in place of head cement. It?s tougher and fills in and smoothes out any thread gaps or bumps better than reg. head cement on quick ties with heavier thread. (BTW you can thin SH with acetone if needed.) I usually put on a wheel for drying to prevent sagging and do several light coats. The consistency of the SH is thicker than the head cement I use on FW, so the wheel helps even things out, other wise you can get a sag somewhere that might throw the tracking of a fly off (or seal the eye).
I?ll use reg. head cement on the heads of large stonefly nymphs, but put a drop of SH on the wing pads. And, unless I?m in a hurry, I also use SH on weighted flies over strips of lead or lead substitute, bound to each side of the hook shank on stonefly nymphs to help get that flat shape and aid in durability, finishing them the next day after they?ve dried. (I tie deceivers the same way, with a coat of SH to lock down the hackle tails overnight, and it?s worked well enough that now I don?t even bother to put a chenille or mylar wrap over the shank, just hide it with the bucktail collar the next day after drying.).
I only use epoxy on Surf Candy type flies, and other flies like Spread Flies, using synthetic fibers where I want to spread out fibers to get a specific shape. You can create a thin fly with a sunfish type of profile for example, with a relatively sparse amount of material (easy to cast, and it?s sort of translucent). This is a great fly to imitate some of the bait we get here like peanut bunker and butterfish with an oval shape. The Surf Candy imitates a sand eel (sand launce out there?) that has a long thin profile, again with a minimum of fibers. The advantage of 5 minute epoxy is that you basically have to hold the fibers in place (takes 2 hands) while the epoxy sets up a little (2-3 minutes) to keep the fibers in the shape you want for a Candy or Spread Fly before you put it on a wheel, so each fly doesn?t kill your whole evening like a longer curing 30 minute type might because of its thinner consistency (or SH which is a lot thinner). I use a VERY thin first coat to set the fibers in position. When it?s dry, I put on eyes, color red gill slits and shade the back with sharpies and put on a heavier second coat to fill in any gaps and seal it and turn it again on the wheel till dry.
I do get some yellowing on the 5 minute epoxy after 6 months to a year, none on flies with SH. The SH is easier and faster to work with than epoxy and doesn?t weigh as much, so I prefer to use it when I can on other stuff. Keeping epoxy flies in a dark box helps delay yellowing, which doesn?t seem to affect their fishability in any event. Epoxy is great if you want to create a thin 2-D profile up/down or side/side (like epoxy bonefish flies). It?s not good if you want to create a 3-D shape to imitate a baitfish like a mullet which has a round cross section (like a big Rapala). That?s where silicone comes in for patterns like Popovic?s Siliclone. It?s an ungodly mess to work with and requires other stuff like PhotoFlo. You can get similar profiles by using spun deerhair heads or hollow ties to push water without turning your hands into Glacier Gloves.
Having said all this, a lot of saltwater tyers, including Bob Popovic, that have tried it, rave about the Tuffleye stuff and it has replaced epoxy for them. It?s an acrylic resin that?s cured with a special blue light (not UV) and eliminates the yellowing and odor of epoxy. The initial start up cost is kind of steep since the light is about $75, so unless you?re planning on doing a lot of ?specialty patterns? that require a material like epoxy for shaping it?s probably not worth switching.
If you go the epoxy route, it?s very important to get the proportions of A and B stuff close to equal. I avoid the plunger type thingy because of this, and use tubes of each, squirting a dime size blob of each side by side for eyeball comparison in a jar lid and mix well with a toothpick. Otherwise you?ll end up with a cloudy or permanently tacky finish. Save the mixing for a bunch of flies to finish off all at once.
Sorry for the long post, had too much coffee. Hope this helps.
peregrines