Dopping with 5-Minute Epoxy

by Jonathan L. Rolfe

I converted from waxes to five-minute epoxy for dopping a few years ago. The reasons I did were:

  1. I have wide temperature variations in my shop at times…(New England). Shellac-based “waxes” become extremely brittle at low temperatures…We know that upon chilling a dopped stone, a quick rap releases it instantly. In warmer seasons, elevated temperatures can make the “wax” fluid, so that a dopped stone in storage can slowly creep. Like the pitch used in optical polishing, these materials are not really solids, but more like a supercooled liquid of infinite viscosity, like glass is. If a penny is placed on top of a pail of polishing pitch, over a long period of time, it will be found on the bottom.
  2. Ease of positioning: With a little simple fixturing, the stone can be positioned perfectly, and adjusted carefully without racing the freezing point of the wax. The fingers are spared burns as well.
  3. Shock resistance: The epoxy, when hardened, has more resilience than cold wax.
  4. Ease of release: Warming the dop while pulling and slightly applying torque (All done gently) will cause the stone to be released at surprisingly low temperatures.
  5. Reduction of thermal cycling: Naturally, the fewer times your stone sees temperature extremes, the lower the risk. When Nature grows our rough for us, there are no guarantees that the materials have been annealed or strain relieved.

The Devcon 5-minute which I have found to be best for dopping is supplied in a dual syringe with blue hardener on one side . This is a different product than the five minute Devcon in the separate tubes, BTW. I find the first one is easier to remove with heat, but if allowed to harden at least 30 minutes, has never failed me.

The entire reason for using the five-minute epoxies is that they are actually _terrible_ adhesives for their intended household purpose! Their high temperature performance is awful..Just right for removing the stone with gentle heat! They are not that great with solvents, either, so a soak in acetone, etc., overnight can soften and swell it till the stone falls off. “Fast” epoxies never develop the degree of crosslinking needed to make a heat and solvent resistant formulation, as do the slower cure formulations. The latter, when used for dopping, can cause great disappointment, because some of them NEVER release the stone unless aggressive solvents like “Attack” are used..

Whenever mixing any epoxy system, always remember that the proportions are critical, as is thorough mixing! Many people who have had bad results have not used the materials properly, or have used outdated materials. The hardeners are highly reactive and degrade at room temperature, especially in the presence of water vapor. The amines are hydrolized to the alcohol and ammonia, and other species. In this sense they are a lot like fish: If it smells really bad, don’t use it. 🙂

The hardener systems are entirely different between ‘fast” and “slow” epoxies. All epoxy hardeners can be nasty, but the fast cures are the worst, among them 4,4-Methylene Dianiline (MDA). Sensitive individuals can have trouble with these fast hardeners if they are left on the skin, BTW, so always wash hands well after using, always measure the amounts accurately of both components and mix thoroughly for predictable results, and never, never bring the fingers near the eyes when using them until the hands are well washed.

Some people have had good results from cyanoacrylates. I have not tested them yet, because I am happy with this particular epoxy. The cyanoacrylates are know to have poor shock and solvent resistance, though. I have, however, used a “hybrid” system, where the pavilion is cut with wax dopping, then the transfer is done with epoxy. This could be the best of both worlds for people because the most critical operation occurs at a comfortable temperature. Warming the wax dop will release the wax before the heat arrives at the epoxy bond enough to destroy it.

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