All wedi Building Board sizes and thicknesses can be used as tile underlayments over concrete subfloors. Modified thinset mortar, combed through with a minimum 1/4” x 1/4” notch trowel, will then provide a ribbed bed into which the wedi Building Boards will be laid. All joints should be staggered so that no seam continues throughout the length of the floor. Apply weights (i.e. tile boxes) onto the surface and where transitions are located while the mortar is setting up. After the mortar has set, wedi alkali resistant fiberglass mesh tape, or wedi Sealing Tape or wedi Joint Sealant should be applied to all seams, then tiling can begin.