Repairing crumbling cement walls is accomplished through a process known as pargeting. Pargeting involves covering the crumbling wall with a layer of plaster. The new plaster layer not only gives the wall a smoother, cleaner appearance, but also serves to prevent water seepage.
- Prepare the wall area
Place a plastic sheet at the base of the wall along the crumbling area to catch any loose material or dripping plaster. Use painter's tape to secure the sheet to the wall.
- Remove loose wall material
Use a wire brush to remove any crumbling material from the concrete surface. Brush downward with long, overlapping strokes to break away any loose pieces from the wall. The removal of the loose material helps the plaster adhere to the wall.
- Mix the plaster
Create a concrete mix to plaster the wall, using 1 part Portland cement, 3/4 part limestone and 2.5 to 4 parts sand. Mix the plaster materials in a large bucket using a wooden painting stick, adding water to the dry mix until the plaster is the consistency of pancake batter.
- Apply the plaster
Dampen the crumbling wall section with water, and then spread the plaster over the wall with a trowel. If the plaster fails to adhere to the wall, it is too thin and should be remixed using less water.