That coil acts as a resistor, meaning it will get hot, hence why over the years the original bedding compound they used broke down over time and why the surrounding material resembles a type of ceramic. I'd bet it's closer to plaster of paris than any type of glue - some sort of hardening cement type of material, same as used in ballast resistors. Not sure I'd try JB Weld on it. It's good stuff but like any other epoxy I believe heat will soften it.