additional grout material on the slates which can then be spread by the applicator so as to form a thin breathable film layer of grout material on the top surfaces of the roofing tiles the applicator attempts to maintain a smooth wet edge on the applied grout at all times see fig6 which shows the various areas of slate roof being treated with the process of the present invention three distinct areas of the roof can be distinguished a an area where the voids have been filled with grout and the outer surfaces of the slates given a thin breathable film layer of the grout material b an area in which the ground has been applied to the crevices and voids but the initially excess grout material has not yet been spread over the outer surfaces of the slates and c an untreated area of the roof this grout spreading step can be efficiently accomplished by using a squeegee or a trowel like tool see fig7 this thin breathable film layer of grout material on the tiles proves to be beneficial in providing a level of surface protection for the tiles for a period of several years the speed of this application process is proportional to the size and spacing of the void between the tiles i e more time and grout are needed to fill a greater number of larger voids given the unique nature of each slate roof the total time periods required.