Concrete block walls, while durable and easy to use as a building material, aren't widely known for their attractive looks. Cover interior concrete block walls with a layer of surface-bonding cement to remove the look of unfinished blocks. A layer of surface-bonding cement also creates a clean surface that's easily decorated further. In addition to creating a smooth surface, spreading the cement onto the block walls adds an insulation layer and increases waterproofing.
Clean the surface of the block wall using a pH-neutral cleaner. Remove all dirt and debris from the wall and repair any cracks in the surface of the blocks. Clear out any cracks using the wire brush and fill the crack with the joint repair sealant, evening out the surface of the sealant with the wall using the putty knife. Allow the sealant to dry for 24 hours.
Mix a batch of the surface-bonding cement large enough to cover 20 square feet of block wall surface, according to the manufacturer's instructions.
Use a damp sponge to wet the surface of the wall slightly, and apply the cement to the wall using a steel trowel. Spread the cement using even strokes to a thickness of about 1/8 inch. Use upward strokes when applying the cement and work in sections, leaving as few lines on the surface of the cement as possible. Cover the full 20-foot section.
Wet a different trowel and use it to smooth the surface of the cement. Work over any lines left from the cement application to create a seamless wall covering.
Repeat the application process, covering the rest of the block wall surface.
Cover the surface when completed with concrete-curing blankets. Attach the blankets to the ceiling and drape them in front of the cement surface. Do not allow the blankets to touch the cement while it is still wet. Wait 48 hours for the cement to cure.
Remove the blankets and allow the cement to cure completely for the amount of time suggested by the cement manufacturer.