Painting an exterior concrete block wall is be a straightforward process. For best results and to make quicker work, have at least one other person work with you. Paint when the outside temperature is higher than 10 degrees C and when the humidity isn't too high. These conditions ensure that the paint will adhere to the concrete and dry properly.
Inspect the wall for effervescent deposits, a white powder that occurs when water has got inside the concrete blocks. If there are no effervescent deposits, skip to the power washing step. If effervescent deposits are present, use a scrub broom and pressure washer to remove it. Because these deposits can be caused by a leaky roof or flashing, be sure to make the necessary repairs prior to painting.
Wash the exterior block wall with a pressure washer. A commercial pressure washer with at least 1134 Kilogram per square inch, psi, is considered ideal for removing paint. Washing the surface thoroughly is necessary in order for the paint and primer to adhere correctly, even if the block wall has not been previously painted,
Examine the wall for large cracks and loose mortar while pressure washing. These should be repaired before priming.
Apply a primer coat evenly. The ideal choice for concrete block is called acrylic block fill primer.
Caulk around windows and doors once the primer is dry. Garcia Paint recommends elastomeric and polyurethane caulk, specifically "non-sagging polyurethane for expansion joints and elastomeric around windows and doors."
Apply a thick, even coat of paint once the caulk has cured. Use a high-quality roller with a thick nap for best results.
One gallon of acrylic block primer covers 100 to 200 square feet. Elastomeric paint is recommended for painting over the primer because it can last twice as long as regular paint. Any type of paint will work; however, acrylic paint is recommended over oil-based paint if not be using elastomeric paint.