How to paint cinder block

a. Surface Preparation:

• if efflorescence is present, remove by hand wire brushing; wear eye protection and gloves; try to identify and eliminate any source of water from behind the block that could have caused the efflorescence
  
• scrape out and widen any cracks; brush out dust, and seal with 100% acrylic or siliconized acrylic caulk; make second application in several hours if needed; check mortar joints carefully and repair or re-point as needed; wall and chimney caps must be sound and continuous; chimney flue should have rain cover
  
• treat any mildew with a 3:1 water:household bleach mixture, leaving it on for 20 minutes and adding more as it dries; wear eye and skin protection; rinse thoroughly
  
• remove dirt, chalk, dust, unbound sand, treated mildew, etc. by scrubbing with detergent and water, and rinse thoroughly; or power wash with plain water, taking care to not drive water into cracks or mortar joints

b. Priming:

• priming is necessary to ensure maximum durability and resistance to efflorescence, alkalinity and mildew
  
• use quality exterior latex primer that is recommended for masonry
  
• do not leave a primer unpainted

c. Painting:

• use top-of-the-line exterior 100% acrylic latex house paint in flat, satin, or semigloss finish, depending on appearance desired; or a quality latex masonry paint