When I was tearing out the old carpet in my first rental, I discovered there was wood flooring underneath. Most of it was ok but there were dark stains in some of the rooms. These were probably caused by liquid seeping through the carpet. However, I was happy I no longer had to spend money on laminate flooring since that was the plan. I'm a general contractor so I figured I'd refinish it. I don't specialize in refinishing wood floors so I went on YouTube and got an idea. It didn't look too bad so I rented the sanders (a large one for the majority of floor and a smaller one for the edges). I soon realized it wasn't that easy. The sanders are very powerful and you can easily make grooves or make depressions if you stay in one spot too long. I did my best and after some practice, sanded away most of my errors. I stained the floor afterwards. I was actually happy with the end result. It wasn't perfect but with the money I saved, I was able to update other parts of the house.
