Sand all the timbers on the floor with a 15-grit sanding sponge. The paint will adhere better to the timbers if the surface is rough, rather than smooth.
Add some water to a cloth and wipe up the dust created by the sanding process. Do not start the painting process until the timbers are dry.
Tape off the edges of the room with painter's tape to make sure paint does not get anywhere but on the timbers.
Roll on the first layer of paint using a paint roller with an extended handle. Start in the furthest corner from the door and work your way back toward the door. Don't roll all the way to the edge.
Paint the edge of the timbers next to the wall using a paintbrush. This ensures a neat finish.
Allow the first layer of paint to dry overnight. Apply a second coat for a richer finish or to completely conceal the timbers using the same method you used with the first coat. Lightly sand the first coat of paint first so the second coat adheres better to the timbers.
Wait overnight for the second coat to dry. Roll on a layer of water-based polyurethane to protect the surface. Do not walk heavily on the floor or replace furniture for about three days.