Q: I’m trying to refinish the hardwood floors in my house. My house is from the 70’s, and this is the original flooring. When I nail down boards other boards pop up a little, making a bigger gap in other boards. It doesn’t level out. It’s wavy.
A: I’m not sure what your question is but it sounds like your floors have been subject to higher than recommended moisture levels over time. It also sounds like they may not have been nailed down well, or were installed over a poor sub floor material such as Aspenite.
Nothing much you can do to change that short of removing the floor, fixing the sub floor and installing a new floor. I would encourage you to hire a professional for sanding and finishing. I’ve seen many such floors virtually ruined by a home owner trying to save money by doing the work themselves with rental machines. For the time, expense and potential ruin of the floor, it isn’t worth it in the end.