A method of constructing a wall of a building by casting in which formwork is erected and concrete is allowed to exude through perforations in the formwork, embedding the formwork in concrete and obscuring it from view. A panel for carrying out the method, a thin-walled sheet with multiple perforations for the escape of the concrete during casting, has brackets or clips to fasten it to the adjacent formwork creating a casting space between the panel and the supporting formwork. Floating the expressed concrete produces a smooth finish.