I have removed 50-year-old carpeting but there remains a thick, hard, terra cotta colored layer of what I presume to be old glue. I have tried using a commercial sander to grind it down but it takes forever and cannot even use this technique on the stairs. Solvents don't work. Has anyone used a heat gun or other method?

Mop the floor to keep it wet, and scrape with a 4" razor scraper.

A drum sander with 24 grit.