Primo Tools 1/8" Square Notch Trowel — Thin Bed, Full Bond, Clean Seams

Waterproofing membrane doesn't want a generous mortar bed — it wants the right one. Comb too heavy and thin-set squeezes out at every overlap, builds up unevenly behind the sheet, and telegraphs through the finished tile. Comb too light and the fleece never fully bonds. The 1/8" x 1/8" square notch splits that difference, laying a thin, even bed that keys the membrane in and keeps your seams clean.

A rigid steel blade holds the notch depth honest across the whole wall, so the coverage is the same in the corner as it is in the field. The same fine notch is a natural for mosaics, backsplashes, and other small-format detail work. Setting uncoupling membrane instead? Step up to the 11/64" square notch, and keep a forged margin trowel nearby for the tight cut-ins.

Why Tile Pros Choose It

• Membrane-ready notch: 1/8" square for waterproofing sheet membrane
• Cleaner seams: Less squeeze-out to fight at overlaps and corners
• Even coverage: Precision-cut notches keep ridges uniform
• Rigid blade: Minimal flex for consistent depth
• Versatile: Mosaics, backsplashes, and detail layouts
• Small notch, big consequences: The cheapest tool deciding whether the shower stays dry

Pro tip: Comb in one direction, set the sheet, and press from the center outward to drive air and excess mortar toward the edges. Check mortar transfer on your first sheet before you commit to the wall.