A method of including the selection of cementitious fiber wallboard panels coated on the exterior surface by a coating of water based acrylic to control the fluid absorption rate therethrough. Such wallboards are installed on a building frame with the adjacent edges of the panels forming narrow gaps for receipt of suitable caulk to such gaps and applying a high build flexible resinous latex emulsion over the coating and joints and allowing it to cure at a rate dictated by atmospheric conditions and the fluid absorption rate of such coating and tape.