Cracked Plaster Walls

By James Dulley

February 27, 2015 4 min read

Older houses were usually constructed with a lot more character than newer homes. Unfortunately, just like the case with people, along with aged character come a few cracks and wrinkles.

Plaster, even with some cracks, is my preferred wall surface. It is a harder surface and resists water much better than drywall. This makes it more washable and easier to apply and remove wallpaper. It is also denser, minimizing noise between rooms.

If you have plenty of time and you are not averse to a messy room for a few days, two people should be able to repair most of the cracks in a home's plaster. It is possible, when using certain joint compounds, to finish the entire job in one day, but don't bet on it.

Plaster, being a very hard material, will crack when the wooden structure beneath it flexes. Many of the cracks probably start from the corners of windows or doors. Although you can fix these spots, they are natural stress-relief areas. Over time, small cracks may reappear.

The quality of your repair job will determine how many years it will be until some of these cracks reappear. Trying to control the year-round humidity level inside your home will help stabilize the structural lumber and minimize additional cracking.

The proper method to repair these cracks in the plaster is not unlike finishing drywall seams. Some people recommend widening the crack and then filling it with joint compound. This is usually just a short-term fix because the wall or ceiling will continue to flex at that spot and crack again.

The best crack repair procedure involves laying fiberglass joint tape over the crack and finishing it with joint compound. If you are really energetic, you can apply large sheets of fiberglass mesh over the entire wall or ceiling and then finish them with a plaster skim coat.

To fix a crack, sand the area over it. Sand an area slightly wider than the width of the fiberglass mesh joint tape. Although this step is not absolutely necessary, it does recess the area slightly. This makes it easier to eliminate a hump at the repaired spot.

When repairing plaster walls, use a professional type of dry powder joint compound. (Mix it with water when you use it.) Ready-mixed joint compound in a tub is quick to use, but it might not adhere to the plaster so well as the professional dry type. It is also more prone to scratching because it does not dry so hard.

Some compounds get hard within 30 minutes of being mixed with water. This is ideal for an experienced builder. Most do-it-yourselfers should select a slower-setting mixture that gives you an hour or two to work with it.

First, apply a 1/8-inch layer of the joint compound over the crack. Press a strip of the fiberglass mesh tape into the compound. Run a drywall knife over the tape, and scrape away about half the compound. When this is set, apply thin second and third coats of compound, spreading them smooth. Using a rubber float, trowel the final coat smooth just before it sets.

James Dulley's weekly column, "Here's How," can be found at creators.com.

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