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After spending two hours laboring over just one 12ft x 12ft room with grit 20 paper (the coarsest available) with a floor sander, followed by a little sanding with 60-grit paper, I am not pleased with the result.

residual polyurethane after sanding

As you see, the old polyurethane is still there in about 50% of the area. I now have the impression that if I wanted to take out the old polyurethane completely, the right tool for the job was a drum sander. This of course requires more careful sanding by maintaining a steady rate of movement.

At this stage I have no desire to restart with a drum sander. I want to move on. Does applying a layer of polyurethane at this point mean that I would see afterwards clearly the marks of the old polyurethane? I'm not sure why it was so hard to take it out. Perhaps it was too old and has hardened extremely well. The sandpaper I was using seemed to lose none of its teeth after use. It's as if it was floating over the hardwood during sanding with a floor sander. I applied my own body pressure to no avail.

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I have tried in the past to use a belt sander. Now I rent a drum sander and finish close to the walls with a belt sander. The preparation is very important for a quality job. Any old poly left may appear yellow when a new coat is applied. If using a oil finish it will be an absolute must to remove the poly because the poly will not penetrate even a thin coat of poly. I know you don't want to restart with a drum but it will look much better and you can use a finer belt Providing a better finish in the long run.

  • I thought (bit.ly/2aEFlB3) that there are three kinds of floor sanders. One vibrates a rectangular piece of sandpaper, the second vibrates a circular piece of sandpaper, and the third rotates a piece between TWO drums. Now after looking at the first image here (bit.ly/2aEsHPw) I see that there is also a fourth kind that rotates a piece of sandpaper tied to ONE drum. Can you elaborate on whether I got the "third" and the "fourth" correct? Does there even exist a kind that is essentially a large version of a handheld belt sander? – Calaf Aug 7 '16 at 16:15
  • Also, can I continue with a "U-Stand Pro Random Orbit Floor Sander" (the kind that uses circular sandpaper)? – Calaf Aug 7 '16 at 16:16
  • My brother used a random orbit floor sander on his floor and did a great job for a first time novice. He rented one with 4 pads it was square in configuration. Some are available with 3 pads that are triangular in configuration, this style would do better getting into corners. – Jack Aug 7 '16 at 16:35
  • In the first link you posted (the one to a previous question), Numbers 1 & 3 are essentially the same thing, big vibrating sanders. Number 2 is the same as your 2nd link, a standard single drum floor sander. – Jimmy Fix-it Aug 7 '16 at 19:46
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Get yourself the random orbit sander style. It is a bit more user friendly where you only need to keep it moving. Drum sanders are, for me, hard to govern how well and where the cutting is doing. These I have used before, real easy to screw up with them.

Back at the random orbit sander. To get a good supply of 20 or 32 grit pads and the other grits as well. Get extra, then get more, you can return the unused pads. Better to have extra than looking for something you have no more of.

You are close to moving on but not yet, a bit more attention with the coarsest pass and you can move onto the next finer cut. Sand with the coarsest until the old finish disappears the do no more for that cut. Change the grit to 60 and make a complete pass over the whole area to remove all the marks left by the 20 or 32 grit pads. I aid myself in how far I need to go with that pass by marking the area with pencil. When the pencil marks are gone, the cut is complete. Do that with each successive grit and your floors will love you for it.

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