I have an 1890's that someone had glued 1970's shag carpet to oak hardwood floors. Also had a maple hardwood floor in the kitchen with several layers of linoleum glued down with the black adhesive. After trying sanding, adhesive remover, paint stripper and scraping someone told me the solution that does work! It will sound counterintuitive but you mix a strong solution of TSP cleaner in a bucket of hot water. Then mop this solution onto the floor keeping it wet for 40 min or so. The TSP solution will turn the glue to mud which can be easily scraped off. When nothing else worked, this took care of the problem. If you leave the oak flooring wet too long, it can warp, but I used this method in 3 rooms and then was able to sand and finish and they turned out beautiful. The maple floor cleaned up beautifully as well! Attempting to sand the glue mess off the floor will fill up sandpaper sheets almost immediately - the TSP method works!!

Kinda looks like vinyl sheet flooring. Either way you must take up the flooring and scrape it very good. If its tile I would rent an air hammer with a flat chisel. After the floor is clean check for dips and bumps ( level is not so important) and level it out with floor leveler. Floating floor is a simpler option but I won't touch the stuff and you will get a more possessional job with engineered glue down. Better resale also.

It depends on what type of wood you have and how old it is. In our last house we had 75 year-old birch, and the new planks we added during a kitchen reno always looked a little different (although not enough to really matter...the planks had differentiations even amongst the original wood.) Of course we did refinish the entire floor at the same time... Oak might be easier! In our current house, there are 60 year old red oak floors. They'd been recently refinished (~3 years ago.) We needed to patch in a large section during our kitchen reno, as we removed walls and relocated the kitchen. We simply bought new unfinished red oak (at Home Depot) and a satin poly my DH hoped would match the existing. He expected to have to try a few different finishes and/or stain, but it actually looks identical just as-is. I can tell you----- staining is not the best answer for the long term!! In another part of this house, a previous renovator used WHITE oak, and then stained it to look more like the red oak everywhere else. When we tried to do a screen-and-recoat recently, when adding some new flooring to an adjacent room, we found we were sanding off the stain. So we had to proceed VERY carefully so as not to remove the stain.... otherwise it would have meant a major sanding of ALL the stain, and then re-staining. It was a bummer because there were some scratches and fading that I'd really wanted to fix, but doing so just would have been too big a project. If you want to be able to do easy screen-and-recoats, selectively sanding more where you need to for repairs, DON'T use stain.

Thanks for all the feedback. @Patricia Colwell - a couple of them are rough. I'm not sure what type of wood it is. If I don't cover them, I'll have to replace them. I don't want to go back to carpet. That back room and those stairs is the last carpet in the house. I was tempted to consider just carpeting the treads (like the second post I made). I was lucky with the main house stairs, it had oak treads and I just had to clean them up. I guess if I want oak hardwood stairs, there is no magic. Hard work or big payout. As for existing treads, I still can't tell if they are under or butted up against the skirt boards. It doesn't make sense to do it that way, It has to just be well fitted treads. It would take a magician to cut those skirts with every level fitting so well. One more question regarding those three odd shaped treads from the first picture. What is the typical solution? Buy extra treads and use an extra one or two cut fastened together? Or do you order a custom boards from your lumber company? Answer to my own question, for those who are just learning like me. I need to buy/build a left hand winder tread set. Rona and many other places carry them. Done! I have no more questions/concerns with this subject. Thanks for the help. Thanks, Mark.