How to Repair Cracks in Plaster Walls – This Old House

Painting on old plaster walls

Kevin O’Connor receives instruction from Mauro Henrique on how to repair drywall and plaster cracks. Before beginning some repairs, Kevin and I discuss where cracks are most likely to appear after explaining to Kevin that the quality of his paint job depends entirely on the prep work.

Painting on old plaster walls | Steps for Repairing Plaster Walls

With the utility knife, clear up the crack to begin the project. Investigate the crack for compound, paint flakes, and other debris, then scrape it out.

Apply a thin layer of joint compound to the crack using the putty knife. Drag the compound downward, pushing it into the crack as you go, starting at the top of the crack. Pull the knife blade across the fracture at an angle to remove any extra compound (not perpendicular to the crack).

Put mesh tape over the newly applied compound. The mesh tape should be gently pressed into the compound bed from top to bottom before being cut with the putty knife.

Apply a second application of compound over the mesh tape right away. Apply the compound, removing any extra, starting at the top of the tape. To give it time to dry, wait 45 to 60 minutes.

Feather the edges of the repair while lightly sanding the repair area to get rid of any high areas and ridges. To get rid of the dust, use the tack cloth.

Apply a third coat if the patch or crack is still noticeable, and when it has dried, feather the edges with sandpaper.

How to Fix Small Cracks in Plaster

Some minor cracks can be repaired using a two-coat method and a flexible patching material without the need for sanding.

By scraping the putty knife over the fissure, make sure it is clear of any debris.

To the crack, apply the flexible patching compound. Push the compound into the crack starting at the top and working your way down.

Since the excess patching compound cannot be sanded, it is crucial to get rid of it. Cross the crack with the putty knife’s blade at an angle (again, not perpendicular). Before letting the compound cure for at least two hours, check that no high spots or mounds were left behind.

After the first application of flexible patching compound has dried, apply a second coat in the same way. Make sure there aren’t any ridges or high spots left behind. Before painting, let this coat dry completely.

Two layers of plaster were used to create the old plaster walls and ceilings. The wood lath, strips that are fastened to the studs and spaced approximately 14-inch apart to form keyways for the brown coat to grab, is covered with the brown coat.

After the brown coat has dried and become firm, the finish coat is applied. The link between the plaster and its wood lath determines the integrity of a plaster surface. Plaster fractures when the bond fails.

Adhesives Can Also Do the Job Well

Big Wally’s Plaster Magic is a two-part glue that was created by Vermont-based plaster restoration specialist Rory Brennan to repair plaster without the need of plaster washers.

Drilling a series of holes in the plaster on either side of the crack and stopping when you reach the lath is how Big Wally’s is applied.

The conditioner, a milky liquid, should then be squirted into the same holes after vacuuming up the dust. This material will be absorbed like a sponge by old plaster.

After that, use drywall screws and large plastic washers to temporarily bind the plaster to the lath by injecting one full squeeze of the heavier glue into each hole. Both the adhesive and the conditioner are odorless and wash away with water. In a day or two, the adhesive hardens.

After it has dried, remove the screws, remove the washers, and use joint compound to fill the holes.

The task is completed with a fast skim coat of joint compound.

The cost of buying a kit that comes with everything you need to fix loose plaster is significantly cheaper than the expense of removing that much plaster, hauling it away, and then hanging and taping the wall or ceiling.

FAQs

Where should I look for plaster cracks?

Above door jambs and window frames is a typical location to look for cracks. They frequently occur at the places where the plaster and drywall meet. Before painting, take careful to look for these kinds of cracks and fix them.

Why do plaster cracks appear?

The walls begin to gradually sway as the home begins to settle. This is due to the fact that the materials in the walls’ construction constantly contract and expand, which might result in cracks.

Which compound—joint or patching—should I use?

The best option for wider cracks is joint compound, which should be applied along with joint-strengthening products like mesh drywall tape. Flexible patching compound is a fantastic option for minor cracks since it will move and flex together with the other building elements.

Resources

The greatest methods for patching and fixing plaster wall cracks are provided by Mauro. His go-to material is Sheetrock® Brand Dust Control Patch and Repair Compound, a flexible patch compound made especially for stress cracks in walls. Additionally, Mauro used Dynamic 2″x150′ (50mm x 45.72m) fiberglass drywall tape.