wrote:

Will all epoxies bond to one another?

There are two (2) types of bonding, chemical and mechanical.

Chemical bonding occurs when a follow up layer of resin is applied
over an epoxy surface that has not totally cured.

Mechanical bonding occurs when a layer of epoxy is applied over a
totally cured epoxy surface.

You appear to be describing old work, thus mechanical bonding will
apply.

A small right angle sander with 24 grit discs will be your friend for
this job.

BTDT, forget the T-Shirt.

Good luck.

BTW, micro-balloons as a filler will do the job, especially when you
lay a piece of glass tape over it.

Lew