The complete removal of old, weathered coatings is not always needed or feasible when repainting a structure. The are several guidelines which should be used when painting over old coatings:

• Remove mold and mildew: this can be achieved 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 all loose or peeling paint by scraping, wire brushing, or another method such as power washing with plain water or abrasive blasting; wear eye protection, gloves and a dust mask
  
• Remove dirt, chalk, dust, mortar, treated mildew, etc. by scrubbing with detergent and water, and rinse thoroughly; or by another method such as power washing with plain water
  
• Dull any glossy paint by sanding with fine (#220) grit garnet paper; wear eye protection, dust mask and work gloves
  
• Adhesion to weathered paints can be difficult in certain cases, and could compromise the longevity of the new coating system. Test patches should be used to check adhesion of the new coating on the weathered surface, where appropriate. In certain cases, complete removal of the weathered coating may be necessary.

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