Gordon,

There's another discussion on seats currently on the forum. Through a bunch of hyperlinks, I came up with the following which shows a wire brush attachment. It looks like it may be brass. I just bought a 4.5 inch grinder too, but the hard disk tends to get caught and dig deeply into the foam.

http://www.kayakforum.com/cgi-bin/Building/index.cgi?review=91165

The seat is very smooth. It could be the softer brass wire brush is gentler and doesn't dig in. I ended up using what is recommended on www.kayakfit.com which is a modified Stanley Surform 21-115 blade. It was much more controllable than the disk, but I have to do a lot of sanding to smooth it out.

Regards,

Steve Pituch