Water Damage Repair for Drywall and Plaster

Before beginning repairs to water damaged walls or ceilings, locate and stop the source of the water leak. If not repaired, the leak will certainly ruin the wall material again.

Use setting–type joint compound for water damage repair, ready-mixed compound will not be hard enough and is vulnerable to any residual moisture in the wall material. The setting and drying times in these instructions assume the use of 30 minute setting–type joint compound like Durabond45®. When using a slower acting compound increase these times accordingly. For help applying joint compound use the techniques on the Skim Coating page.

Water Damage

Water will affect plaster and drywall differently. A plaster surface will erupt as water activates the alkali in the plaster of paris. This process causes a bubbling, crumbling surface.

When drywall is suddenly and briefly soaked the paint and paper drywall tape will usually bubble but the drywall will be undamaged except for stains. When exposed to a lot of water, drywall tends to warp as the gypsum swells. As the gypsum dries, it hardens into a bulging wall or ceiling surface. This will be true of plaster with gypsum board lath also. Bulging gypsum like this will always need to be cut out and replaced to restore a flat surface.

Repairs

To repair water damage, all loose wall material must be removed. This may require cutting the damaged area out with a drywall knife or drywall saw in the case of gypsum board plaster and drywall. See Drywall Repair Large Holes for replacing bulging gypsum board.

Chipping the damage with a putty knife is usually the best way to remove water damaged white and brown coat plaster. After all loose, damaged wall material has been removed, test the paint coat immediately surrounding the area for failure. If the paint film comes off easily when a putty knife is slipped under it, it should be removed also.

Remove dust from the cutting and scraping process and coat the water damaged area with shellac or shellac primer–sealer. Use one with a white pigment added, such as Kilz® or Zinsser's B-I-N® Primer–Sealer, to help hide stains and make finish coating easier.

To repair shallow water damage to drywall and plaster walls and ceilings, skim the area with several coats of mud using these Skim Coating Techniques. Replace damaged drywall tape and use this Crack Repair or this Drywall Finishing process to refinish drywall seams.

To repair lath plaster with deep damage to brown and white coat use the following repair method.

Repair Large Holes in Lath Plaster

Mix setting joint compound to fill the damaged area using the instructions on the Skim Coating Techniques page. Fill the void to overflowing with mud. For large areas mix consecutive pans of mud until the entire void is filled. Work quickly before the mud has time to set.

Immediately skim the excess mud from the surface of the repair area using a straight edge. Scrape the collected mud from the straight edge and return it to the mud pan. Discard the unused mud or use it to make more repairs before it sets.

Let the mud set for about half an hour and lightly sand the area. Don't try to smooth out the surface here, just knock off any peaks or ridges in the mud.

Skim coat the area several times to build a smooth surface over the damaged area. Mix a small batch of repair compound and spread it over the surface of the repair and onto the wall immediately surrounding it. Skim the excess mud off using the joint knife held at a 30° angle. Return the excess mud to the mud pan. Let the mud set for 30 minutes and skim coat again.

Reverse the direction of the skimming strokes with each application to help eliminate any ripples or bubbles in the surface. Repeat this skimming process until the surface of the repair is smooth. Depending on the degree of damage, this could require up to 4 or 5 applications of mud. See Skim Coating Techniques for more.

Allow the final coat of mud to set and dry for an hour or more and sand lightly, feathering the edges into the surrounding surface. Brush any dust from the surface before priming and painting. If you are using flat latex finish paint, you can use it to prime the repair. If you are using semi-gloss or other shiny paint, prime with flat latex or a latex primer first.