Abstract: A plant and method for the manufacture of cementitious products, viz. cast concrete roof tiles (T), the plant comprising a mixing station (2) where the constituents of a cementitious composition, less an air entraining agent, are admixed under atmospheric pressure and further mixed under a partial vacuum of 200 to 340 mBar after the addition of an air entraining agent, the plant also comprising a molding station (4) where the tiles (T) are cast in a gang-mold (6) before being cured in a conventional autoclave for up to 10 hours at 45 degrees C. The cured concrete roof tiles (T) are de-molded after curing and conveyed to a surface preparation zone (12) where a primer coat of a water based epoxy and a surface coating of a water based emulsion paint are applied to at least an upper surface in use of the cast concrete roof tiles (T). The admixed cementitious composition has a Ford Cup flow of between 40 and 60 seconds and a slump test of between 180 and 220 mm.