Prior to painting, a concrete surface should be free of contaminants, efflorescence or laitance, loose concrete and mortar, and poorly adhering paint.

• 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, or other crack filling material suitable for the particular application; check mortar joints carefully and repair or re-point as needed
  
• 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
  
• Where appropriate, use of SSPC SP-13, Surface Preparation of Concrete, should be used. The standard gives requirements for surface preparation of concrete using mechanical, chemical, or thermal methods, and are applicable for all types of cementitious surfaces, such as cast-in-place concrete floors and walls, precast slabs, and masonry walls.
  
  

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