Engineered flooring boards are manufactured with a hardwood or fiberboard core and a surface veneer of hardwood. They look like real hardwood when installed and are less prone to separation and movement than real wood, but the veneer on engineered flooring is thin, ranging from 1/32 to 3/16 inches. When the time comes for refinishing, you can't sand off as much of the surface as you can with real wood, or you may end up sanding right through the veneer, so it's best to use an orbital sander. This may take longer, but it will save you from costly and time-consuming accidents.
Remove the baseboards from around the perimeter of the room with a pry bar and set them aside.
Wash the floor with a high quality hardwood floor cleaner. This will remove grime and old wax that can clog up the sandpaper. Mix the floor cleaner with warm water and mop the floor with the solution, then let the floor dry completely before proceeding.
Separate the room from the rest of the house by hanging sheet plastic in the doors. Turn off the central air system so sanding dust doesn't get pulled through it and contaminate other parts of the house.
Fit an orbital floor sander with coarse sandpaper and sand the floor, starting in the middle and working towards the edges. Keep the sander moving, and sand in one place only until all the old finish is gone. Start with 50-grit paper and check it frequently. If you find that it clogs, or that the finish is not coming off, change to 36-grit. Use care when sanding with 36-grit paper. It will wear the surface rapidly.
Sand in corners and along the edges with a hand orbital sander fitted with the same grit sandpaper that you used with the flooring sander. Use a floor scraper to remove finish from corners that you can't reach with the sander. Pull the scraper towards you to remove finish, but don't let the corners of the scraper dig too far into the wood. Touch up areas you have scraped by sanding by hand.
Vacuum the floor, then re-sand it with the next finer grit sandpaper. If you started with 36-grit paper, move up to 50-grit and if you started with 50-grit, move to 80-grit. This will remove sanding marks from the previous pass. Vacuum and repeat with the next higher grade (either 80-grit or 100-grit). The last pass with the sander should be with 100-grit paper, so you'll make one more pass if you started with 36-grit.
Vacuum the floor again, and then wipe it down with a damp cloth to remove dust lodged in the wood grain and the gaps between boards. Finally, stain and refinish the floor.
In some cases, you may prefer to finish the sanding with 120-grit sandpaper to further smooth the floor. There is little danger of sanding through the veneer with such a fine-grit paper.
Very thin veneers of 1/32 inch cannot be sanded without wearing through to the core. The best you can do is to touch up the finish by scuffing it with a floor buffer fitted with a 120-grit sanding screen and adding more finish. Sanding a floor creates a lot of dust, so wear a dust mask. Wear safety glasses if your eyes are sensitive.