Concrete blocks are a widely used building material because they're fairly cheap and are easy to work with. The drawback is that they have a rough, unfinished appearance. You can solve this problem by finishing the wall. You have several options for this, including framing out the wall and installing drywall, or by adding stucco. You can also plaster the wall. Plaster is a durable material that comes in a variety of colors, and you can texture it any way you want.
Patch any major holes or cracks in the concrete blocks with concrete patching compound.
Power-wash the walls to remove any dirt or grease.
Nail strips of 3/8-inch wood lath to the wall along the top, middle and bottom with masonry nails.
Measure the surface area of the wall to determine how much plaster you will need. For the base coat, 1 cubic foot of plaster covers approximately 17 feet of space on the wall. You need about 1 cubic foot of damp sand, one-third of a bag of cement and one-third of a bag of lime to make 1 cubic foot of plaster.
Dampen the wall by misting it with water. Do not soak the wall; you just want to add some moisture to the concrete blocks.
Mix the plaster according to the instructions on the packaging.
Load some plaster onto the hawk. This is a metal tray with a handle on the bottom that is perpendicular to the tray.
Apply the plaster to the wall with the trowel. Start at the bottom of the wall and work your way up. Hold the trowel at a 45-degree angle, reducing it to about 30 degrees as you sweep the plaster over the wall. Press the plaster into the wall so that is forced into the surface of the concrete blocks. The layer of plaster for the base coat should be about 3/8-inch thick.
Screed the surface of the plaster by placing a wood or metal straightedge on the wall, using the wood lathe strips that you installed in Step 3 as a guide. Drag the screed horizontally across the wall with an up-and-down motion to get a uniform depth of about 3/8 inch for the entire wall. Add more plaster to any low spots exposed by the screeding, and screed the wall again.
Remove the wood strips from the wall.
Wipe the surface of the base coat with a mason's float after the sheen on the surface has disappeared but before the plaster has hardened. Use a swirling motion with the float. Allow the plaster to set overnight.
Mix the finish coat of plaster and apply it to the wall the same way that you applied the base coat. Make the finish coat 1/8- to 1/4-inch thick.
Texture the finish coat. You can use a paintbrush, sponge or float to apply whichever texture you choose.