How To Repair A Water-Damaged Plaster Ceiling With Joint Compound

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If you have a water-damaged plaster ceiling, with chipped and cracked bits of plaster falling from the damaged area, then you may be feeling at a loss on how to repair it. Fortunately, you can repair the damage yourself if you are willing to use the right materials and tools. Below is what you will need as well as how you can perform the repair:

Tools and materials needed

Step-by-step procedure

1. Remove loose bits of plaster - To successfully perform a repair on a damaged section of plaster ceiling, you must remove all the loose debris from the plaster. Use a stiff-bristled paint brush to scrape away these small pieces and dust particles. Once you finish with the brush, dampen a grout sponge with tap water and wipe down the area to remove the tiny remaining particles. Dampening the plaster surface will also help increase the adhesion between the subsequent layers of joint compound.

2. Prepare the joint compound - Next, pour about one quart of water into a five-gallon bucket and then add about an equal amount of joint compound powder to the water. Stir the water and powder mixture using a paddle mixer attached to an electric drill; as the mixture begins to thin, pour in additional joint compound powder a little at a time. Continue to mix and add powder until the mixture reaches a consistency similar to peanut butter.

3. Add the first layer of joint compound - Once you have mixed the joint compound, scoop some onto a plaster hawk, but be careful not to overload the hawk. Next, scoop a small amount of joint compound off the hawk onto your finishing trowel. While standing below and slightly behind your work space, apply joint compound to the damaged part of your ceiling. Pass the trowel across the surface from all directions to ensure the joint compound is pushed into the damaged area. Make your applications light and avoid placing too much joint compound at one time to prevent uneven drying or cracks. Pass the edge of the trowel over the edge of the damaged area and feather the compound onto the undamaged ceiling margins. This will help blend the repair and make it less noticeable once you are finished.

4. Sand the first layer and apply the second - After applying the first layer of joint compound, allow it to dry for 45 minutes until it is just set. Next, sand the joint compound lightly using a 200-grit sandpaper; sand using a sweeping motion and run the sandpaper across the entire repair area, overlapping the margins slightly. Follow up the sanding by wiping down the surface with a damp grout sponge.

Once you have sanded and wiped down the joint compound layer, look for areas where the first layer of joint compound did not properly set or where there are indentations or other imperfections. Apply a second thin layer of joint compound on these spots first, then spread the compound across the rest of the repair site. Be sure to keep this second layer even thinner than the first one, as you want to avoid the possibility of cracking or chipping. Again, allow the layer to dry for at least 45 minutes, then sand the joint compound and wipe it down with a damp sponge.

5. Slicken the surface of the repair - The last step before priming and painting the damaged area is to "slicken" the surface of the dried joint compound. This will provide a final smoothing of the repair site and create a seamless blend with the margins.

To slicken the repair, take a metal yardstick with a straight, smooth edge and wet it with clean tap water. Hold the long edge of the yardstick against the edge of the repair site, then slide the entire yardstick over the site in a slow, continuous motion. Repeat this motion, but approach from a 90-degree angle to your original starting point. Allow the repaired area to dry for at least 24 hours, then prime and paint it as desired.

Note: While these instructions work for a small patch job, more severe water damage will require the help of a professional water damage repair company.


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