Our south-facing wall on west coast Scotland is of Durisol 365 blocks, with a render finish. How to seal the render in the window reveals is a puzzle. The plans call for Parex Parmurex OCR and painting, or Parex Monorex GF. I would like to seal the walls and door/window openings before fitting window frames and sealing them with mastic as usual. Any suggestions welcomed - 300 sq metres to cover!