First-time homeowner-we just bought a house with hardwood floors, from 1922. There is a stain and a topcoat(maybe a type of varathane). We rented a commercial sander and when we started to sand the topcoat would warm up, then ball up and harden to the sandpaper and the floor. We had to stop, scrape this stuff off the paper and the floor. Needless to say in two days of work we didn't get very far and didn't even get down to bare wood. The floors are made of fir. Any suggetions on our next step.