Ceiling tiles are relatively fragile. A slight bump with a sharp object is liable to leave a gash or long scratch on the face of a tile. For many people, the only recourse is to replace the entire tile, but another solution for a small, damaged area is to simply repair the problem. Most repairs can be made without even removing the tile and take only a few minutes.
Step 1 - Identify the Cause
Identify the cause of the problem for the tiles before you start. If the tile is water stained, locate and repair the source of the leak. In a bathroom, make sure that an exhaust fan is installed. Ensure that it functions properly. If you are correcting scratches, be sure that the cause of the scratching has been corrected, such as adjusting a cabinet door or tightening a strap or clip of an object that has been rubbing the ceiling. It will not do any good to repair a spot if the problem has not been corrected.
Step 2 - Define the Paint Area
Using painter's tape, cover any surfaces that you do not want to accidentally spray. This includes the gridwork as well as any fixtures mounted to the ceiling. Do not apply even painter's tape to the face of a drop ceiling tile as it could peel away the factory paint, necessitating further repairs.
Step 3 - Paint the Ceiling Tiles
Ceiling paint comes in an aerosol can with the nozzle pointed upwards, making it easy to apply. Always shake the can vigorously for 3 to 5 minutes before using. Aerosol paints settle when stirred. The pigment must be agitated thoroughly in order to get the correct color and tint when spraying. Hold the can 8 to 12 inches from the damaged spot, and spray in light strokes. Allow the tile to dry for 30 minutes after each light coat. Compare how well the color matches before applying another coat of paint.
For plastic or metal ceiling tiles the process is nearly the same, except that a suitable ceiling paint may not be available. If possible, take an existing tile out of the ceiling, and have your local hardware or paint store mix a pint of matched color. Using a small, fine-tipped paintbrush, touch up the damaged area. Allow the first coat to dry before applying a second coat.
WARNING: Put on safety glasses and face mask before you start applying ceiling paint, and make sure the work area has adequate ventilation.
A Note on Ceiling Tile Repair
Repairing a ceiling tile does not mean it will be just like a brand new one. A scratch on the face of the tile will leave a slightly ragged looking spot. Wash your hands thoroughly and dry them well. Using your thumb, lightly smooth the damaged area before you paint it. As long as the paint color is a close match, the spot should be largely invisible to the casual observer. If the damage is so severe that the paint cannot conceal it, your only alternative is to replace the tile.