If you properly paint a concrete block wall it will last for years with little upkeep. Here are 5 basic steps to help you do the job successfully.
Step 1 - Clean the Wall
There are two basic types of finish on concrete block—smooth and split face. Regardless of the finish and whether the concrete has already been painted, the cleaning procedure is very similar. Begin by using a pressure washer. Don’t use more than 2000 psi on an unpainted wall or 2500 psi on a previously painted wall or you will damage the concrete or mortar.
Plain water is fine for the removal of dirt and dust as well as loose and peeling paint. Add a bit of mild soap or laundry detergent to the stream for more difficult efflorescence (a whitish, crystalline substance) deposits and other oily stains. If that doesn’t work, use a scrub brush or hand scraper to manually scrape off any remaining stains and loose paint.
Step 2 - Repair the Mortar
Missing and damaged mortar must be repaired before moving onto priming. Use a premixed acrylic mortar patch unless you want to spend an additional 2 days mixing and drying the mortar. Mend and repoint joints as needed.
Step 3 - Prime the Block Wall
Use acrylic block fill primer over either unpainted or previously painted concrete in order to seal its pores. Make sure to prime all mortar as well. The texture will determine the amount of primer and paint needed. Smooth face concrete requires considerably less primer; typically you can cover about 200 square feet per gallon of block fill primer on a smooth face, and about half that amount on split face.
Step 4 - Caulk and Seal
Before painting, make sure to seal all cracks and gaps. Any area large enough to let water in, which is usually 1/16 inch or larger, should be caulked. The best type of caulk to use in this case is elastomeric caulk. For caulking the expansion joints you’ll need to use a foam backer rod.
Step 5 - Painting Concrete Block
Now you’re ready to paint. The best type of concrete paint for exterior walls is also elastomeric while 100 percent acrylic paint is a second-best option. Make sure to apply 2 coats to achieve the highest durability.
The type of paint you select for interior concrete walls will depend upon the use of the room as well as its décor. Paint with a sheen or gloss will be easier to maintain, for example. Apply the paint to the concrete block with an airless sprayer and then immediately back roll it, working in sections along the length of your wall.
You’ve now completed painting a concrete block wall and there’s nothing left to do but sit back, relax, and admire your handy work.