The best way to strip fenders is using ---enviro tech--- system in brampton. they dip the fender into a chemical solution thats heated to 180 degrees that removes all tar, paint, bondo, lead....anything not iron.
Then they dip it again into another tank where the alkaline solution and a negative electrical charge is applied completely removing absolutely any remaining rust. Formerly the USA based process was known as REDI STRIP in canada and usa. They power wash the parts before returning them too you.
Complete bodies..: porsche..jag xke, .fords , mini's and what ever else you can think of are dipped in their 10 foot wide by 20 foot long tanks.
I am taking my roadster cowl there very soon to undergo the process and also my roadster rumble seat foot area floor piece. Its not cheap, but better than soda or any other material blasting. Liquid gets in where blasting cannot.
mike