If you need to sand a hardwood floor, a drum sander is the tool of choice to do the job. A drum sander is a large power tool with detachable sanding belts that will remove a layer of the floor surface by abrasion. The abrasive sheets can be quickly replaced. Since you will probably not do such jobs on a regular basis, you may want to just rent a drum sander, usually available for around $40 a day.
Step 1 - Check and Clean Your Floor
Before you begin sanding you should check your floors over for any protruding nails or objects that might damage the sanding belt. You should remove or hammer down any nails or tacks or remove them completely with pliers. Any nails must be hammered below the level of the floorboards. You should also make sure that there are no loose floorboards. If there are, then secure them with a hammer and nails. You should then sweep your floor clear of any dirt and debris.
If your floor requires removing a layer of varnish, you should start with a coarse grit between 40OC and 80OC grit—OC standing for open coat abrasive. This will prevent the belt from clogging too quickly. For a bare wood floor or after the floor is sanded down to the bare wood and is in reasonably good condition, you'll then need to use sandpaper with a finer grade abrasive at around 120 grits in order to smoothen out the wood surface and to remove the deeper scratches from the coarser sandpaper.
Step 3 - Prepare for Sanding
Open all the windows in your room make sure that it is well ventilated. You should also seal around the door to prevent any dust from spreading into the rest of the house. Put on your eye goggles, particle mask, ear protectors, and make sure you are wearing old clothes as sanding a wooden floor is messy. If you are sanding the floor using the diagonal method, proceed with step 4. If you are sanding along the lengths of the floorboards skip Step 4 and proceed to step 5.
Step 4 - Sanding the Floor (Diagonal Method)
If you are sanding the floor diagonally you should start in one corner. Tilt the drum sander before you switch it on so that the abrasive belt isn't in contact with the floor. Sand at 45° to the direction of the boards until you reach the adjacent wall and tilt the sander when you get to the wall before turning 180° and continuing with the next pass in the opposite direction next to the previous pass. Continue in this manner until you reach the opposite corner of the room and it's all been sanded. Each time you reach the wall, tilt the sander to avoid the belt damaging the floor.
When you have finished you will need to begin sanding again in the adjacent corner to the one you started with sanding perpendicular to the previous direction. This will remove any waves caused by the sanding in the initial passes and also ensure that the whole floor has been fully sanded. You can complete any missed areas with a small sander. Continue to step 6.
Step 5 - Sanding the Floor (Along the Lengths of the Floorboards)
Tilt the drum sander before you switch it on so that the abrasive belt isn't in contact with the floor. Lower the sander and sand along the length of the floorboards from one wall to the opposite end of the room. When you reach the wall tilt the sander up to avoid damaging the floor. Follow this process for the whole floor area by moving over for every successive pass making sure that each pass overlaps the previous one to prevent misses. Use a small sander to complete any missed areas.
Step 6 - Cleaning
When you have finished sanding, sweep the floor to remove any dust and vacuum using a soft bristle attachment. You can then pass a damp mop over the whole floor area.