Particleboard is a composite wood that is used to construct furniture, door cores, floors and cabinets. The wood is made from sawdust or wood chips and glue. When particleboard gets wet, it can swell or even disintegrate. Manufacturers use particleboard because it is less expensive than plywood. Unless the water damage is significant, particleboard can be repaired after getting wet. Particleboard that will be exposed to moisture should be treated with paint or waterproofing material to prevent further damage.
Dry the wet spot by using a hair dryer. Using a heat gun may create temperatures that could ignite the particleboard. If you have time, you can let the particleboard dry naturally.
Sand the water-damaged area with a medium-grit sandpaper by hand or by using an electric sander until the spot is flush with the dry areas. Finish sanding with a finer grit.
Vacuum or sweep up the sawdust created when sanding down the damaged particleboard. If the surface is likely to get wet again, apply a waterproofing material and allow it to dry.
Dig out the particleboard's soft spots with a sharp object like a screwdriver or knife if the particleboard has loosened and is powdery. Once the spot has thoroughly dried, vacuum the residue or sweep it thoroughly.
Apply wood filler, following the directions on the can or tube. Use a putty knife to smooth the top of the repair to make sure that the surface is level with the rest of the particleboard.
Sand the surface once the wood filler has thoroughly dried. Vacuum the dust away from the surface. Apply sealer if the area is likely to get wet again.