Water is the ultimate enemy of a mobile home floor with a subfloor made of particle board. A small amount of water from a leak can soften and weaken particle board, and over time, it becomes weak enough to crumble under a small amount of pressure. Particle board cannot be repaired and should be replaced with plywood, which is more durable. Repairing a water-damaged floor in a mobile home is a matter of removing the floor covering, cutting out the damaged particle board and replacing it with stronger plywood.
Roll back the carpet or cut out the linoleum over the water damage, and remove it to expose the particle board subflooring. You can reuse the carpet, but you will need to replace the linoleum with new floor covering.
Find the joists under the particle board by feeling the floor and looking for rows of screws securing the subfloor. Use a pencil to mark where to cut the sub-flooring.
Use a circular saw to cut out the soft spot all the way to the nearest joist on both sides. Set the blade less than 1 inch to keep from damaging the joists. Remove screws in the repair area with a drill, and use a pry bar to pry up the old particle board. Remove any damaged insulation, clean the area of debris and install new insulation.
Use a circular saw to cut 2-by-4-inch boards to fit between existing joists if you need more support for your floor patch. Screw supporting joists to the old joists with a drill and 2-inch galvanized screws. If your repair is at the wall line and the joists are too far under the wall line to attach the plywood, add one or two support joists so that the plywood can be screwed to the joist.
Use a circular saw, and cut the plywood to fit in place. Run a bead of construction adhesive on the top of the joists, and put the plywood patch in place on the joists. Use a drill and 2-inch galvanized screws to secure plywood to the joists. Replace the floor covering by rolling back the carpet or installing new linoleum.