When I was in high school one of my brothers and I had a contract at a local office building. There was an engineering firm that used an electric eraser on their drawings and it spewed tons of eraser crap which they immediately ran over with the rollers on their chairs grinding it into the VCT.
We stripped with a Steel wool pad under a 175 and just plain water. It was a good thing the legs on that engineering firms desk were really strong. The 175 dug in a time or two and moved the desk a little--well maybe a lot....