How to Finish a Block Wall

Block wall finishes include plaster, stucco and paint.

Concrete block walls were first used in the U.S. in the 1830s, when they were hand- pressed into molds. Over the years concrete blocks evolved and were made with cavities to improve insulation and help prevent moisture from seeping through them. Today their production is automated, and they are one of the most popular building materials in use. They are used to build homes, offices, garages, barns, garden walls, dumpster enclosures and more. Consumers can choose from a variety of colors and textures, but block residences are most often finished with plaster, stucco or paint.

Things You'll Need

• Plaster, stucco or paint
• Concrete block primer
• Polyurethane caulking
• Water
• Wheelbarrow
• Soap
• Wire brush
• Trowel
• Scrubbing brush
• Paint spray gun
• Stucco sprayer

Instructions

1. Decide on a finishing medium. Plaster must be applied by hand with a trowel. Stucco and paint can be sprayed on with a spray gun.

2. Clean the block wall. Scrub it with a wire brush to remove any hard protuberances of mortar. Follow up with a stiff brush and degreaser detergent. Be sure to remove any efflorescence--a white powder that leaches out of the concrete--and finish with clean water. Exterior walls can be sprayed with a pressure washer or hose.

3. Prime and prepare the wall. Paint it with concrete block primer to help reduce the porosity of the concrete and prevent efflorescence. Fill around all windows and doors with polyurethane caulking.

4. Mix the plaster or stucco premix with water in a wheelbarrow to the consistency of soft dough. Dampen the wall and hammer a length of thin wood across the wall in the first section to make a screed, which will prevent the plaster from slipping down. Apply to the wall above the screed with a trowel using a sweeping motion. When it has started to dry, move the screed to another section and smooth the plaster with a float.

5. Blend the stucco premix with water for spraying to a slightly wetter consistency if you decide to apply it this way. Mask the windows and doors with plastic. Spray the stucco across the wall using a sweeping motion. If the stucco seeps out of the nozzle when you are not pulling the trigger, it is too wet--add more stucco mix. If it doesn't come out, it is too dry--add more water. Keep the sprayer perpendicular to the wall and about 12 inches away. Lightly trowel the stucco to smooth it.

6. Apply the paint with a brush, roller or spray gun instead of the plaster or stucco as an alternative or over the plaster or stucco, using as many coats as may be necessary. Remember to mask door jams, doors and windows first. Stucco and plaster come in a choice of colors, and it may not be necessary to paint over them.

Tips & Warnings

• Wear safety goggles and closed shoes at all times while working and overalls to protect your clothing.

References

• House Painting Info: Painting Concrete Block
• Stucco Guru: Cement Plaster Over Concrete Block Walls
• Mortarsprayer.com: Spraying Stucco