Minor water damage on your ceiling includes some staining, bubbling, and/or peeling plaster and paint. While this may look absolutely hideous, it may be completely cosmetic. Before you begin your own water damage repair work, make sure your efforts will not be destroyed by a repeat wetting of the materials. Then the job is as simple as three steps.
1. Peel and Scrape Away the Flaking, Bubbling, and Peeling Paint and Plaster
Since this stuff is trying to crack and peel away anyway, just help it along. A paint scraper and a light hand are sufficient. Gentle side-to-side motions will remove the damaged paint and plaster without removing too much of the plaster and drywall underneath. Once all the cracked, peeling, and bubbled plaster and paint have been removed, examine the ceiling and test for "mushy" wet spots. If there are none, move on to Step 2.
2. Add Fresh Plaster Where Needed
In spots that were a little more damaged than others, you may lose a little more plaster in the scraping process. That is okay. Mix up a fresh batch of wet plaster and use a mason's trowel to apply it to the spots that need a little fill-in patch. Since you are working on a ceiling, make sure the plaster is thick and sticky, like oatmeal, so that it does not drip down and off the areas you are trying to patch and even out. After the fresh layers of plaster have adequately dried, move to Step 3.
3. Repaint, Sand and Repaint
If your ceiling had paint on it before, it will need paint over these areas again. The good news is that now you can buy anti-mold and anti-mildew plasters and paints for this exact problem (i.e., water damage on your ceiling). Use these special kinds of paint to paint over the repaired and patched areas, and then paint the entire ceiling for added measure. (It will help block out any mold or mildew spores that may have spread in the attic space above your ceiling.) Sand it smooth, and paint a second time. Now your ceiling should be good as new.
If you are concerned about a really serious mold and mildew problem in your attic, by all means contact a professional water damage remediation specialist. He or she can take a look using special scopes to see if there is a serious problem and offer some solutions if anything disconcerting is spotted.