Pressure washing with water or sand blasting probably will be necessary to prepare the surface prior to the application of any stucco materials.  The choice really depends on the condition of the walls and the type of stucco you’re planning to apply as to which is the best choice for your project – there’s really no hard and fast rule and should be evaluated on a case by case basis.  Pressure washing (Hydro Blasting) and Sandblasting are general terms to describe the act of removing fine bits of material at high-velocity to clean a surface. Silica sand is the most commonly used material for sandblasting, but any small, relatively uniform particles will work.

When applying stucco, one does not want to trap dust, dirt, or bubbles in a previous layer of stucco or paint, or other imperfections under the new layer. By pressure washing or sandblasting, which is a technique of launching water under pressure or small bits of abrasive sand at the surface at a high speed, all imperfections are loosened and can then be easily washed off. Wet sandblasting means water is used in the technique to remove debris such as paint, tex-cote or old stucco, from a structure. This creates a clean and relatively uniform surface that is ready for a redesign with new stucco. Pressure washing and wet sandblasting are the most common sandblasting techniques.