Hi again. Need some advice. Home is 100 years old. Removed carpet. I rented a sander that has four discs on bottom. Once I started to sand, sander started to leave a build up of varnise or what ever. I had to use a razor to remove. Also, on bottom of sanding pads (using 40 grit) wax, varnise, or stain was gumming up on bottom.