I installed engineered hardwood floors in my living room in the instructions it said to put polyurethane on the floor when finished so that's what I did but now some spots on the floor are spotty and some are smooth and shiny what should I do. How can I take the polyurethane off the floor.

A couple of things come to mind:
1. Did you thoroughly clean the surface prior to applying the polyurethane? An improperly prepped surface will almost always give you problems.
2. How many coats of polyurethane did you apply? I just did floors throughout my house (pine upstairs, oak down). After the first coat (and even the second coat on the pine) the finish did not look consistent. I used three coats, which is recommended for oil-based poly. If you used a water-based product, you may need as many as five coats.
3. I was advised, and some manufacturer's instructions also advise, to apply the second coat directly over the first, sanding only between the second and third coat. I did one room sanding between each coat; I think this is worth the effort in final outcome. I used a drywall sanding pole with an 80-grit open drywall screen--it worked like a champ.
4. What gloss are you using? High gloss can show more of the results of an improperly prepped surface.
5. How did you apply the poly? Most recommend a lambswool applicator, although a turkish towel can be made to work well.
6. I thinned my first coat (3 qts. Poly/1 qt. mineral spirits).

I guess all of this is trying to prevent you from having to take the poly off the floor. The only way to do that is to sand it off. Get back with some more details and we may be able to help you save your job without sanding and re-doing.

You will need to make sure the poly has fully cured, read the can because it can take weeks. Sounds like you may have some dust that settled on the poly before it dryed or even some fuzz from your appliactor. Lightly scrub the dull spots with 0000 steel wool and vacuum. Hit the entire floor with a tack cloth and apply another coat with a lambs wool applicator.

I know that it has been a while, but this is an issue that concerned me, and I was unable to find a definitive answer to this question - just a lot of speculation. I think I now have an answer, and thought I would share. I will post this to a few other sites, as well, because I want people who have questions, to get answers.

I have had problems with wrinkling, especially at the end joints, when water is spilled (sometimes for very short periods of time) onto my newly installed engineered hardwood floor. For this reason, I conducted a test on remaining scrap boards that I had. I used Mercier 1/2" thick engineered Oak, with plywood and HDF substrates. I clicked them together to form a (roughly) 4' x 2' sample floor and placed it upon a piece of remaining underlayment. I covered one half of the sample with Minwax semi-gloss poly and let dry for one day. The other half I left with the factory finish.

I will say that my personal impression was that the poly side was more attractive in sheen than the factory side. It looked more natural, like 3/4" hardwood (though, it clearly still looked like engineered). I guess, to be vague, I thought it applied evenly and gave the wood more "character," and less of a plastic look. I had no issue with adherence (I cannot guarantee that this will be the case for another brand of EH, but just test a piece and wait a few days).

I used this sample to perform a water spill test. I dumped several cups of water on the surface of both sides of the sample. I kept reapplying water, evenly, over the surface to account of seepage and runoff. I did this for about 10 minutes and then just let it sit for another 10. Within 10 minutes, noticeable wrinkling was occurring at every end joint on the factory finish side. Nothing from the polyurethane side. Within 15 minutes, The wrinkling on the factory side was significant, and now there was some wrinkling on the side seams, and even in the middle of individual boards. Wrinkles extended out from one end seam, around 3". The average was around 1" from the end. At the end of the test, there was zero wrinkling or any noticeable water damage to the polyurethane side.

To me, it was conclusive evidence that a coat of polyurethane can significantly reduce or eliminate wrinkling and damage caused by minor spills. I think that it is clear that the manufacturers can do a much better job at addressing this problem of water seepage. They market their floors as "just as durable" as 3/4" and "Long-lasting." However, one pipe burst, or dishwasher leak when you are at work or sleeping (heck, even a minor liquid spill that you do not catch within 10 minutes), and your floor will be destroyed, I guarantee it

I plan to do a scratch test and a long-term (2-3 day) standing water test later in the week and will post my results.

I have photos and will post. I posted in this old thread, because it is one of the first that pops up when you do a Google search on this matter, and one that I went to looking for answers.