The people who lived in the house before up carpeted over the existing hardwood floors. When the carpet was installed, they glued the carpet pad to the floor. We now want to refinish the wood floors. We have scraped as much glue off as possible. We have been told to sand the rest of the glue off. What grade of sandpaper should we use? What do we do after that?
What your friends meant was that you will need to sand the whole floor down to the bare wood. You are best advised to hire a professional for this sanding part of the operation. He will have the 200 pound, 220 volt drum sander that will do a smooth pleasing job on your expensive wood floor. And hopefully he will also have the years of experience behind him, so as not to hack and gouge your nice hardwood floor. His machines cost about 10,000 bucks, so expect to pay about a dollar a square foot for a sand only job.
The rental floor machines are TOYS, and leave nasty gouges and chatter marks across the floor. How does one expect to learn this rather delicate and skilled trade, on the job while you hack and hew at your own floors? This will diminish your enjoyment of you floor and lower your houses resale value. But it is always a good idea to finish the floor your self. This is often where the pro, in his hurry to complete his work and get paid, will slip up. I always recommend 3 coats of oil modified polyurethane, allowing a day between coats for drying, and always scuff sanding and cleaning between coat, for adhesion of the layers.
Be sure to read my article available in the search box at the top of this web page on hiring contractor.