General epoxy information from a hobbyist. I am not an epoxy engineer.
These are general truths so far as I know. I've used epoxies all my adult life.
PS ADDENDUM: you cannot re-pour epoxy onto itself after the "amine blush" has occurred;
you'd get no bond then. In case of pouring over a previously epoxied surface, one must sand, roughen, tooth, key,
the surfaces! The West System people are so strong and respected in their line of marine epoxies, I bet that by now they have a comprehensive website containing all this information and more ( last used their products in 1999, and they were so excellent with customer help/information. I bet it's all online today.
=+The slower-setting the epoxy, the stronger and more heat resistant it is.
Marine grade (West System) epoxies are excellent. But so are any quality epoxies that are designed to set slowly. I generally use the hardware store syringe type stuff (slow set!!!!), but for my controller job I wanted the "best": a slow set designed for laminating table tops that must resist hot plates and platters.
I had a small kit on hand from many years ago. Beat buying a $50 or thereabouts, West System brand kit, and seems to give fine, equal results.
=Any liquid epoxy can be admixed with an almost endless variety of fillers in order to thicken the material against being runny. Anything from metal powder, plastic dust, talc (easy to sand). Again, the West System brand and other pro brands offer a variety of powders to admix into their liquid epoxies.
Glass microbeads are the most inert filler of all, and easy to sand and shape.
=Epoxy putties are filled epoxies with fillers of various sorts.
=Pure, liquid, slow setting epoxy is the least hygroscopic of all kinds.
=Slow setting epoxies are the most heat resistant.
=All epoxies completely soften to cheese-like strength and consistency in heat, and I mean in low heat: sub- 250F turns all pure epoxies so soft as to be removable by wire brush or dental pick. There is no extant "600F" epoxy, JB Weld claims are lies. Overheated epoxy, so long as it is not burned by the heat, returns to its original state of hardness upon cooling down again.
=Some epoxies are rock hard and would be considered brittle if the substrate is flexed.
=Some epoxies are less than rock hard, and will endure some flexing.
=Bonding: Absolute cleanliness. Solvent wash more than once. The slightest trace of oil, invisible,
will compromise the bond.
=More about bonding: some materials have a natural affinity to bond fully (if they are clean) to epoxy.
=Many materials, mostly plastics of polyethylene type, cannot chemically bond to epoxy; they are "non polar" to epoxy.
In these cases a semi-reliable mechanical bond can be gotten by coarse sanding of the surfaces.
=Epoxies of the slow set, hard kind, are the least hygroscopic of all coatings...far superior to water ingress, long term, than polyester resins, which otherwise seem so similar.
It is for this reason that premium watercraft are gel coated with epoxy and not with the much cheaper polyester resins of yore: Polyester resin boat gel coats eventually blister and fail if the boat is constantly kept in water.
RTVs: silicone rubbers are excellent aids, but are, for sensitive work, sometimes not suitable: they are all hygroscopic. That is, if the item is going to be submerged in water long term, the silicone "rubber" stuff will take on a considerable percentage of water, though it will not blister or "leak" massive water through to the substrate.
I favor the marine epoxies, slow setting (I used to use West System when I worked with old cars and their wooden frames. Nothing is better for wood reinforcement and filleting and even for "saving" rotted wood, than a very slow epoxy: it will wick well into well-dried wood before it sets up.
For my submarine ebike controller, see the gradual progress at my "show your ebikes thread".
I think it will work. ONLY the controller board itself is "potted"; and I won't be relying solely on
the table-top coating resin chosen for this job.
See my thread for updates, reasonings, and best guesses. I'm not an expert, but I do have some
slight experience with epoxies for some decades, and hope to have a submarine-capable ebike before long. The controller enclosure: completely open to the cooling, drying breezes. It will be a cool little eZee controller, thanks to waterproofing the part that counts: the board and its wire-take off points.
fwiw, hope this helped,
Reid