DIY Repair Water Damaged Plaster

• Repair Water Damaged Drywall
• Repair Deep Plaster Damage
• Repair Blistering Paint
• Repair Water Stains

This page is about repairing water damaged plaster, to repair water damaged and bulging drywall use this link. 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 repairs to plaster. 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 wall repair 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 mixing and applying setting compound use the techniques on the skim coating page.

About Plaster Water Damage

When plaster gets wet it will usually erupt as water activates the lime in the putty coat, causing bubbling in the surface. This damage may be minor, surface bubbling or it can involve the whole plaster coat including the brown and scratch coats.

As the plaster dries, the putty coat may form a rock hard shell that must be chipped away with a hammer and chisel–blade joint knife. With severe water damage, the sand in the brown and scratch coats may crumble and fall off the wall as the plaster dries.

Removing Water Damaged Plaster

To repair plaster water damage like this, all loose wall material must be removed. Scrape all damaged material from the area using a putty knife. This includes bubbling or peeling paint, plaster putty coat and any brown or scratch coat involved.

Remove any loose, crumbling plaster from the lath substrate and scrape back to solid material in the surrounding surface.

Scrape Peeling Paint

Test the paint coat immediately surrounding the area to see if it is loose. If the paint film comes off easily when a putty knife is slipped under it, it should also be removed back to sound paint.

Remove the Dust

Remove dust from the chipping and scraping process and coat the whole damaged area with shellac–based primer–sealer or an alkyd wall primer. With water damage, a sealer like this is essential to block residual moisture that would otherwise inhibit bonding of the repair compound. This could result in bubbling of the new joint compound.

Sealing Water Damaged Plaster

Coat all affected surfaces including the surrounding wall paint. To help hide stains and make finish coating easier, use a primer–sealer with a white pigment added, such as Kilz® or Zinsser's B-I-N® Primer–Sealer. Let the sealer dry completely before beginning repairs. Shellac primer will dry in about an hour while alkyd primer will take about 12 hours to dry completely.

Repairing Water Damaged Plaster

To repair deep water damage to plaster walls and ceilings involving the brown and scratch coats, use the process at repairing lath plaster.

To smooth out the pits and cavities in shallow damage to a plaster surface, use several skim coats of setting joint compound. Spread mud over the whole area using a joint knife to butter the surface with about ¼inch of mud. Immediately skim off the excess mud to fill the damage and leave a thin coat around the edges. Ignore any ridges left by the edge of the knife blade and half–filled pits in the first coat. It will take at least a few coats of mud to fill and cover all the damage.

Let the mud set until it hardens (30 minutes to an hour) and scrape off any protruding ridges left by the joint knife. Lightly sand the area with course to medium sandpaper to remove any other bumps, etc. in the surface. A completely smooth surface is not necessary here, just remove any protrusions that would cause bumps in subsequent skim coats.

Brush off the dust and wipe the area with a clean, damp rag or sponge to remove the sanding dust. Skim the area again with a second coat of mud. Apply the mud perpendicular to the first coat to help level the surface. If the first skim coat was applied horizontally, apply the next with vertical strokes. Check the skim coating page for more detailed instructions on smoothing walls with joint compound. Let the last skim coat set and dry for about an hour before sanding with 120 sandpaper. Prime the new patch with primer–sealer and let it dry completely before touching up the paint.