Pruning

• If your brick retaining wall is holding back dirt, you may have grass or vines growing through the gaps in the brick. Before beginning the application process, trim this vegetation from the wall using hedge trimmers. Use an edger to cut grass overgrowth away from the top and bottom of the wall. Once you've eliminated all vegetation from the wall, wash the brick with a pressure washer.
  
  

Primer

• Paint won't stick to your retention wall unless the brick is coated with a bonding primer. Ordinary latex primer may crack and peel from exterior brick surfaces. For a durable foundation, apply an acrylic latex primer base.
  
  

Caulking

• Once you've applied primer, you may notice tiny holes or crevices between the bricks and within the mortar. To prevent future vegetation overgrowth, seal these gaps with acrylic caulk. Use a caulking gun to force the caulk into these areas. Wait at least four hours for the caulk to dry, and look over the area to ensure the caulk didn't shrink too much. Add more caulk if necessary.
  
  

Paint

• Once you've taken the necessary steps to prepare the retaining wall for adhesion, you may apply the appropriate type of paint. Latex paint won't last on exterior brick retention walls, which are subject to wind, rain and direct sunlight. For a lasting finish that won't fade or flake, apply an acrylic latex paint.
  
  

Application

• Although you can use a sprayer to apply primer and paint to the retaining wall, the weak flow won't do a very good job of filling the porous mortar between the bricks with paint. For best results, roll each coating onto the wall, and touch-up the brick with a nylon paintbrush.