Abstract: A brush for a rotary floor machine is especially adapted to clean grout on tile floors. The brush includes a disk having a plurality of first and second bores arranged into a plurality of rings disposed about one face of the disk. Each ring defines an arcuate pattern of alternating first and second bores. The first bores are angled inwardly towards the center of the disk, preferably 5.degree. from a line normal to the plane of the disk. The second bores are angled outwardly toward the periphery of the disk, preferably 5.degree. from a line normal to the plane of the disk. Tufts of bristles disposed within the first and second bores thus form pairs of overlapping bristles.