Cabinets in a kitchen or bathroom get splashed by sinks and faulty plumbing, leading to water damage. Condensation also creates issues with wood cabinets. The damage can be subtle changes in the finish or major issues when shelving becomes saturated, causing it to crumble or sag. You can repair almost any problem resulting from water damage.
Lacquer, which is typically used on cabinets, turns white when exposed to water. It might take a few weeks or even months, but in time, the lacquer looks spotted or appears with large blotches on end panels, doors or the cabinet's face frame. For a quick fix, try rubbing down the spots or blotches with almost any type of furniture polish that contains oil. It can be lemon oil, linseed oil, walnut oil, mineral oil or tung oil. The oil penetrates into the lacquer to bring back the natural translucence of the material, restoring it to its natural color. Rub the oil on liberally, let it remain on the surface for about an hour and wipe it off. If the white color resists, repeat the process until the oil works its magic.
Sanding is the next option if you can't remove the white color with oil-based products. Start by using 100-grit sandpaper attached to a sanding block. Focus on one door or drawer front, one end panel or use tape to isolate one piece of the cabinet's face frame. For convenience, remove doors and drawers and place them on a flat surface. Sand off the lacquer using the sanding block. Sand parallel to the grain with short strokes. The lacquer will stick to the block, so change the paper frequently to keep the sandpaper working efficiently. You'll know that you have removed the lacquer when the surface of the wood appears dull and you can't see shiny spots. If you haven't sanded off any stain, you don't need to restain the piece, but if the stain appears blotchy, apply a matching stain. When the stain is dry, spray the wood with a single coat of aerosol lacquer from a can. When the first coat is dry, sand the wood with 180-grit sandpaper and spray it again to finish.
Damaged shelving is almost always the result of leaky plumbing or a faulty gasket around the water faucet. The water or damage goes unnoticed until the bottom shelf becomes saturated, crumbles or warps. Before doing anything else, find the source of the water and repair it. Then remove the shelf by prying it out in pieces if necessary. Insert the tip of a pry bar under it, or if that's not possible, cut a hole in the shelf with a jigsaw and insert the pry bar into the hold. Remove all the staples and screws and clean out the chips and debris. Measure and cut a new shelf using 3/4-inch particleboard or plywood. The new shelf probably won't fit through the doors of the cabinet, so cut it in half. Insert both halves into the cabinet and use two-by-four blocks to support the joint where you cut the shelf in half. Screw the shelf to the cabinet frame and where the blocks support the joint between the two halves. Add finish to the new shelf before installing it.
If the water damage has gone unnoticed for a period of time, chances are that the overlay flooring under the bottom shelf has also become warped or crumbled. You can access it after you remove the cabinet's bottom shelf, which is located 3 inches above the floor. Damage of this type might appear as a small bulge in the vinyl covering under the toe-kick where it emerges from under the sink cabinet. You might be able to feel it with your toes when you're at the sink. This means that the particleboard overlay -- which is under the toe-kick frame, below the cabinet's bottom shelf -- has become saturated. If the overlay flooring has any type of vinyl floor covering, water has leaked into the overlay via any hole or seam where plumbing emerges from the floor. Use a utility knife to trim the vinyl flooring around the inside perimeter of the cabinet and peel it off and remove it. Cut around the perimeter of the overlay with a chisel and hammer. Remove the warped or crumbled pieces of overlay by prying it out in pieces. It might come off in small chunks. Pull out the nails or staples, cut new piece of particleboard overlay and install them in pieces to replace the damaged overlay. Use construction adhesive to glue the original piece of vinyl on top of the overlay, just as it was before.