Before you begin sanding, cover everything possible with plastic sheets for protection from the dust that will be generated. The new boards will not be even, so the purpose of the first sanding is to level the surface of the entire floor. Use a drum sander with 20-grit sandpaper for the first sanding, and sand at a 45-degree angle from the grain of the wood. Sand from right to left, progressing by 2 to 4 inches for each pass. Right-to-left sanding is important because the sander's drum is tapered to sand deeper on the left side.
Remove as much dust as possible and repeat the diagonal sanding a second time with 36-grit sandpaper. Use an edge sander with 36-grit sandpaper to sand the edges next to walls.
Fill any gaps between the boards by using a trowel with a mixture of wood dust and resin. Trowel the mixture as evenly as possible without any material rising above the boards
After the filler has dried completely, sand again using 36-grit sandpaper, working the drum sander perpendicularly to the grain. Sand the edges of the floor with the edge sander and 36-grit sandpaper.
Remove the dust and repeat the sanding using 60-grit sandpaper. Repeat with 80- and then 100-grit sandpaper. If there are still small scratches remaining on the floor, an additional sanding with 120-grit sandpaper may be necessary.
Before finish is applied, remove all the dust coverings and vacuum everywhere there may be any dust. Lines and logos should be painted onto the floor before any finish is put down. Make sure that the paint is totally dry before proceeding.
Tack the floor at least two times to clean the surface and remove all possibility of dust contamination; this is done by placing Turkish towels over a dust mop frame. The towels are kept damp with mineral spirits, and the floor is swept just as it would be dust mopped.
Both oil- or water-based stain and finish are acceptable coatings for gym floors; however, it is vital to follow the manufacturer's directions carefully. Do not use any fans because they will cause the top of the finish to cure before the bottom. Fans can also cause unwanted lint and dust to collect in the wet finish. Working with the grain, apply the stain using lamb's wool applicators. Allow at least 12 hours for the stain to dry before applying finish.
Apply the finish with either lamb's wool applicators or E-Z Way gym finish applicators. Allow at least one day between coats and put down a minimum of three coats. Keep all foot traffic off the floor for at least five days to allow the finish to cure and harden properly.