remove GRP

A 6" disk sander w/36 grit works real well. A disk sander is NOT a
random orbital thingy - all it does is spin a 6" disk in one direction.
Makita has a nice el-cheapo (less than $100) that should take years of
abuse (or at least about 5 times as much as any Ryobi tool - and I like
some of Ryobis tools...).

Disk sanders are significantly lighter than grinders and don't spin
quite as fast. It's easier (and cheaper) to put on new grinding/sanding
media, and they can be used for pretty delicate work if you practice
the knack.

Rufus