SCHLUTER DITRA TROWEL - 11/64 X 11/64 SQUARE NOTCH For DITRA use the DITRA trowel, which features an 11/64" x 11/64" (4.5 mm x 4.5 mm) square-notched design, is recommended. It is good practice to periodically lift a corner of the membrane after embedding it in the thin-set mortar to check the fleece for full coverage. DITRA-TROWEL features a 11/64" x 11/64" (4.5 mm x 4.5 mm) square notch