Q: I just had my oak engineered floors refinished by professionals. Everything looked great. Days after black spots started appearing in one room. The spots are getting bigger and more are appearing each day. This room is on a second floor, so no water problem.
A: I can only make a guess on this. It sounds like water but as you say water is not involved. Then I would suggest a fungus, probably present right from manufacturing. Perhaps they used a water based finish which re activated it. I would call the guys back and have them assess this. You can also contact the National Wood Flooring Association who do have inspectors. They also have a huge repository of information and have likely come across this issue before.
If you take this course, I would be grateful to know what is concluded.