Hi this is about Red oak in front hall. We moved in ten years ago and the floor was in decent shape. Started to fade, sun related and traffic related.
There were always lines of lighter and darker stain that were perpendicular to the wood boards. An inch or so thick. Alternating - Light dark light dark. I was told that they were caused by some bad sanding when the previous owners of the house restrained the wood.
I Just had the floor done and the lines are still there. The contractor says it’s not on him - that there is something wrong with the floor joists or something that sounded like bs. I think it was a poor sanding job originally that was not fixed this time.
What do you guys think?
http://s349.photobucket.com/user/loup29/media/93D1666C-1627-4995-B0CA-AB5F0A576F1E_zps464urgpd.jpeg.html?filters%5Buser%5D=146909095&filters%5Brecent%5D=1&filters%5BpublicOnly%5D=1&sort=1&o=0

There are many reasons why there are sanding marks like these.
The best work will not show like this. Sometimes it is because the right machine did not finish the sanding. A machine like a Trio will remove this type of mark. It can cost over $5000.
Not bad work, but not the best.