thanks colour republic,i thought 6mm was the thinnest in backer boards,also not sure what you mean by dogtooth comb,say i was doing a horizontal strip of two say,i could get the tiles up yo mosaic height,then depending on how thick the tiles are in conjunction with the mosaic thickness,spread rapid set with a 3 or 4.5 mosaic trowel,then butter the mosaic strips with a 3 or 4.5mm mosaic trowel,is that the jist of what your saying,also would you adhesive the wall horizontally,and then adhesive the strip of mosaic vertically,regards darren