Short definition
Tanking is the process of waterproofing a wet-room or curbless shower by applying a continuous liquid-membrane (or sheet-membrane) layer over the floor, walls, and curb area before tiling. Creates a “tanked” enclosure where water can pool, drip, or splash anywhere within and stay contained. Term is UK-origin; now standard US practice for wet rooms.
What it is
Two product categories cover almost all residential tanking work:
- Liquid waterproofing membrane. Roller- or trowel-applied; cures to a flexible rubber-like film. RedGard (Custom Building Products), Hydro Ban (Laticrete), Mapelastic AquaDefense (Mapei). Coverage roughly 50 to 60 sq ft per gallon; cure time typically 24 hours before tile.
- Sheet membrane. Adhered with thinset; pre-formed sheets (Schluter Kerdi-Membrane, Kerdi-Band for seams) bond to the substrate. More forgiving on pinholes; more demanding on overlaps.
Both satisfy UPC 411 (shower compartment must be waterproof) and IRC’s tile-substrate-must-be-waterproof requirement. WA adopts via WAC 51-56 / 51-50.
Cost ranges:
- RedGard 1-gallon: $40 to $60.
- Schluter Kerdi-Band: $25 per 30-foot roll.
- Schluter Kerdi-Membrane: $250 to $400 per 108-square-foot roll.
- Pro labor for tanking: $5 to $15 per square foot of tanked area.
Why it matters to a homeowner
Tanking is the highest-leverage step in any tile-shower or wet-room install. The substrate (cementboard) is water-resistant but not waterproof — without tanking, water reaches framing through the panel within years and rots the structure.
A homeowner doesn’t usually do the tanking themselves but should know whether the work happened. Pro installs document tanking with photos before tile goes down — ask for that documentation, or specify it in the contract for any wet-room or curbless-shower remodel. Inspectors check for tanking as part of permitted bathroom remodels in WA.
For DIY tile-shower projects, RedGard or Hydro Ban over cementboard is the most accessible path: roll on two coats, let cure 24 hours between, verify pinhole-free, then thinset and tile. The cost is small relative to the rest of a tile-shower budget; the protection is large.
Common failure modes
- Pinhole in liquid membrane. Leak below; very expensive remediation. Two coats minimize risk.
- Inadequate overlap at seams (sheet membrane). Water wicks through; specified overlap (usually 2 inches) is not optional.
- Tile installed before tanking is fully cured. Bond failure between thinset and membrane.
- Substrate not properly prepared. Membrane delamination.
Common variants
- Liquid tanking (RedGard, Hydro Ban — paint or roll on) vs. sheet tanking (Schluter Kerdi — adhered membrane).
- Wet-room tanking (entire bathroom) vs. shower-area tanking (just the shower).
- Tanking vs. backer-board with vapor barrier (older method). Modern preference is full tanking.