Plaster Ceiling Patching Steps
A leak from roof damage or even from an overflowing sink on the second floor can cause damage to the plaster on your ceiling. You can't simply paint over it, since either paint won't cover the damage completely or the stain will bleed through the paint. The following can help you repair the damage so your plaster looks like new again.
Step 1: Remove the Damage
Plaster walls have lime, which sometimes reacts with water and creates bubbles on the surface of the damaged plaster. You can't simply scrape off these bubbles and paint over the damage, since the plaster is permanently damaged and will likely continue to crumble. Instead, use a metal putty knife to carefully dig out the soft plaster, stopping only when you reach hard plaster.
Step 2: Create a Seal
Although the area may seem clean and dry once the damaged plaster is removed, there may still be some moisture trapped in the wall. The following will help prevent it from becoming a problem. First, use a slightly dampened rag to wipe up any dust from the removal of the damaged plaster. Next, spray the entire area with a plaster primer, which is also sometimes called a plaster sealant. This comes in a spray can, similar to spray paint, and you only need a single coat. It forms a seal so no remaining moisture can leach into the new patch and cause issues.
Step 3: Patch It Up
A joint compound made for use on plaster walls is sufficient for fixing the damage. You will need to fill in the damaged areas with the compound. Then, scrape it smooth to the surrounding wall surface using your putty knife. If the repaired area is wider than the blade of your putty knife, use a flat board to scrape it off level. Once dry, sand the patched area smooth with a fine grit sandpaper. If the surrounding plaster is textured, apply a thin coat of plaster over the patched area and then use a rag or the edge of the putty knife to mimic the texture.
Step 4: Paint Over It
Once everything is dry, you can paint over it. First, paint over the patched area with a latex paint primer, extending slightly beyond the patch. Then, paint on your first coat of paint once the primer as dried. Allow this coat to dry and then apply your final coat. Your patch should blend in with the rest of the ceiling.