I have a 1918 farm house and I am trying to redo it to original condition. I am in the process of refinishing the hardwoods floor and am having problems. I have clean the floors with TSP and started sanding. However, in the sanding process I am having areas of "acrylic-like" substance appear. They are areas about the size of quarters and are very difficult to remove. I am changing sand paper often and vacumming. Any ideas as to what is causing this? Any suggestions? Thanks for your help.