Mobile home flooring is generally not the best of quality. The subflooring is usually a wafer board type of material, which is wood pieces and sawdust molded together by a gluey substance. If there are water leaks that seep down into this board, it will crumble and become weak. This calls for replacement of the board, since a repair of this wafer substance is out of the question. We want to do so with higher quality materials so that it hopefully does not happen again. This calls for 3/4 inch plywood, and it will be laid down over the wafer board, creating two layers of flooring (and added insulation since wood is an insulator) with no removal of the wafer board subfloor (and no damage to floor joists). If plywood receives a water spill or leak, nothing happens.
Repair Mobile Home Floor
Clear the room of all furnishings and then carefully remove the floorcovering. If it is vinyl, it will probably need to be replaced. If the damaged spots are under carpet, carefully pull the carpet loose, prying up staples. If tacks are used, a nail puller can be used. Pull up the carpet as well as the padding. Roll the carpet up and place it somewhere outside the room. Inspect the padding. If the subflooring was wet, the padding may be moldy, so you may want to buy new replacement padding if this is the case.
View the bare subfloor. You will be able to see the damaged areas where water caused crumbling. Use a tape measure and measure the width and length of the room. This is how much plywood you need to buy. Sweep the floor to get rid of staples or tacks and then go to a building supply store and purchase enough sheets of plywood, nails or wood screws (galvanized won't rust if they ever get wet). Get lengths long enough to go through two layers of wood flooring (old layer and the new). Get wood filler and some sandpaper if floorcovering is vinyl.
Deliver the plywood sheets to your home. You can cut the plywood to fit the measurements outside to keep the dust level down. Mark the measurements with a pencil and cut with the jigsaw. Carry the plywood pieces inside and lay on top of the wafer board subflooring. Check for knotty areas in the plywood. Turn this side face down to insure a smoother surface. Place sheets end to end with no gaps. Screw (or nail) down tightly to the floor joists, and place a woodscrew every 14 to 16 inches through both layers of wood. (Using more will insure that the floors will not creak when walked on). Counter-sink nails or screws and put a dab of wood filler in each little hole if vinyl flooring is being used.
Check for knotty areas that might need wood filling (if you are putting vinyl floor covering down). You will need to fill the holes or gaps with the filler, then sand smooth to insure no bumpy areas showing through the vinyl. Be sure to sweep up all the debris from sanding. If carpet is going down over the replaced floor, no wood filling is needed. If you determined that the padding was ruined, you can now put the new carpet pad down, tacking it just enough that it doesn't move when the carpet is placed back down. You can now replace the carpet that was saved, tacking down the perimeter all around the walls.
Stand back and take a look. One last thing to do is to install the threshold in the room entry doorway. This is because the 3/4 inch plywood is now sitting on top of the old floor, making it just a bit higher. The threshold's purpose is to insure a smooth entry so that no one stumbles.