Mobile home floors are generally made with one layer of particle board which sits on floor joists. When particle board comes in contact with water, it becomes weak and breaks down, resulting in a soft spot in your floor, which you can feel even under carpet. Soft spots occur frequently under doors and windows where water leaks are common. The first step in repairing soft spots under doors and windows is to plug the leak. If you make the repair without fixing the leak, you will have more water damage to your mobile home floor and another repair job to do.
Remove the floor covering--the carpet or vinyl flooring--from the damaged area. Roll the carpet away from the work area. Peel sheets of vinyl flooring back by hand. Scrape and pry peel-and-stick tile off the floor with a floor-scraper tool.
Cut out the particle board that is damaged with a circular saw using care not to cut through the joists--2- by 4-inch supports under the particle board. Use a circular saw to cut along the wall. Cut out an area that is larger that the soft spot. On average, the area you cut should be about 48 to 64 inches wide by 16 to 25 inches deep. Remove any screws from the particle board. Use a pry bar to remove the particle board.
Remove old staples or bent nails from the joist surface with pliers or a hammer. Scrape the top of the joists with a putty knife to remove any old adhesive.
Add a joist using a 2- by 4-inch board cut to size for additional support if there is no joist on the edge of the wall or if the existing joist is slightly under the wall line. Use a drill to screw the new joist to the existing joist with 2-inch galvanized screws. Reinforce weak joists or build new joists 16 inches apart where extra support is needed--such as the entryway at the front door. This will keep the floor from squeaking when you walked on it. Clean the area of dust, dirt and debris. Replace damaged or old insulation.
Cut a piece of 3/4-inch exterior grade plywood with a circular saw to fit the area. Use a drill to screw the plywood to the joists every 6 inches. Replace the floor covering or install new floor covering. If the repair is in front of a door, replace the door trim after the floor covering is installed.