Can California Stucco/Concrete Finish be applied over rigid insulation board?
Yes, but only with a base coat of FSB first. The insulation board must be roughened with a wire brush and the joints must be taped with Masco and fiberglass mesh tape. (Note: roughening with a wire brush is only required for extruded polystyrene like the blue Styrofoam or pink Formula R boards. Roughening is not recommended if the foam board is expanded polystyrene like white beadboard). The FSB must then be mixed with straight C-21 and applied up to 3/8″ thick. Allow the FSB to dry for 48 hours before applying the finish coat of California Stucco or Concrete Finish .
