This will very much depend on the wear layer of your engineered floors, on average, and depending on your refinisher, 0.75 to 1 mm of material can be expected to be lost each time the floors are refinished. This means that a floor with a 4 mm top layer can be refinished 2-3 times if done properly. Since wire brushed and hand scraped floors can lose some of their texture throughout this process, it is important to go over what kind of changes to your floor you can expect with your contractor/refinisher prior to starting.