Kerosene works but is slow and messy. Sometimes you can peel it off with
a putty knife if it is old and hard. This usually works better when it is
cool and less tacky. On the other hand you can scrape most of it off with
a little heat but won't end up with a clean surface. Heat from inside is best.
Whatever you do try not to set it on fire.

If the floor is rusty it may be that the stuff isn't stuck to it too well and
you can peel it off in chunks.
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George Downs Bartlesville, Heart of the USA!