If the floorboards of your house are old, it might be time to give them a fresh coat of stain and reseal them. To prepare them for this, you must first sand the floorboards down to the bare wood to get rid of the old surface and expose the fresh wood that will absorb the new finish. Sanding a room's floorboards will normally take an afternoon's worth of time and a few pieces of equipment.
The main piece of equipment you'll need for sanding floors is a floor sander. This is a very heavy, standing machine about the size of a big vacuum cleaner or a small lawnmower. It contains a motor which vibrates or rotates a piece of sandpaper quickly over a large area of floor. Floor sanders come in several varieties - drum, belt, orbital, disc - and can be rented at most home-improvement stores. Each type of sander has its pros and cons - talk to the rental department about which type will best suit your needs.
Some people may find the floor sander to be a bit unwieldy. For small projects, or if you have a lot of patience, you can use a smaller hand-held belt sander, which does pretty much the same thing as the stand-up machines, but on a smaller scale. Also, you may need an edger if your main sander is too large to run flush along the walls or reach into corners.
You will have to make several passes over the floor with increasingly fine sandpaper to get a smooth surface. Your floor sander will take specially fit sandpaper, and you will use four different grades of sandpaper total: 20 to 36-grit, 50 to 60-grit, 80 to 100-grit, and 100 to 120-grit. Pick up the appropriate paper when you rent the sander. Install and change the sandpaper carefully, while the sander is unplugged.
Sanders are extremely noisy, and even with dust collecting bags, they can generate a lot of wood dust. So wear ear protection, goggles and a construction mask. Close or cover doors to other areas of the house, and open the windows - try putting a box fan in the frame of an open window to draw out dust. Drape sheets over any permanent fixtures.
The First Pass
For the first pass, install 20 to 36-grit paper: it's a coarse grit used to take off existing stain and varnish. Start in one corner of the room and slowly work your way across the room to the other side. Work your way back and forth across the room in rows, overlapping the previous row by one board. This should get the majority of the existing stain off. You may have to sand next to the wall manually or with an edger, as it can be difficult to get the large sander that close to the wall.
Smoothing and Polishing
Repeat this process three more times. Each pass, use a finer grade of sandpaper. First, switch to 50 to 60-grit, then 80 to 100-grit, and finally 100 to 120-grit sandpaper. Each pass will leave scratches, and the next finer grade will make them shallower, but you have to go from the rough to fine sandpaper in gradual layers. Also, as you are sanding, make sure to keep the sander moving steadily across the floor and do not pause it over one spot, or it will dig into the wood. If you are not careful, you will end up putting a hole or dent in your floor that cannot be repaired.