Why tanking matters
Wet room (floor-level shower without screen, drained via linear or point drain) by design exposes entire bathroom floor + wall zones to water continuously. Without proper waterproofing: water migrates through tile + grout + adhesive into substrate; saturates structural floor (rot, decay, damp); penetrates ceiling below (stain, mould, structural damage to room/flat below); promotes mould growth. Catastrophic failure: substrate failure → tile lift, floor collapse, ceiling damage £8,500–£35,000 repair + insurance claim. Insurance: tanking specification + certified install evidence required for damp/escape-of-water claim acceptance. Manufacturer 25-year guarantee available with certified installer using complete system (substrate + tanking + tape + drain + tile + grout — single manufacturer's system). Wet room over flat below (block of flats): freeholder consent + leasehold compliance required; never DIY tank in flat-above-flat scenario.
Specification + install
Substrate: standard 18mm plywood subfloor + 12mm cement-board over (Hardibacker, Marmox, no-more-ply, Knauf Aquapanel); £25–£65/m². Wall: standard plasterboard inadequate (gypsum absorbs water + swells); strip plasterboard in shower zone + replace with cement-board 12mm; install full-height. Tanking membrane: liquid 2-coat application (Aquadec, BAL Tank-It, Mapelastic, Dural Aquadec) — brush or roller on first coat, 2-hour cure, second coat 24-hour cure before tiling; tape internal corners + joints with manufacturer-specific waterproof tape; reinforce drain perimeter; integrate to drain flange. Linear drain: stainless steel grate flush with finished tile level (McAlpine LinearTM, Tek-Drain, Wedi Fundo Riofino); 22mm waste; trap; routed to standard 50mm waste pipe + connection to SVP. Slope: 1:60 minimum fall toward drain across entire wet zone. Tile: porcelain non-slip R10/R11 rating; micro-grout (Mapei Ultracolor Plus); sealant at floor-wall junction (Mapesil AC silicone, not grout).
Critical details + heritage
Critical detail areas (most failures originate at): (1) floor-wall junction at corners — reinforce with corner-piece + manufacturer waterproof tape both directions; (2) door threshold — water naturally migrates toward dry zone if slope incorrect; use floor-recessed threshold trim with sealed barrier; (3) shower head wall mounting — waterproof grommet around supply pipe penetration through cement-board; (4) drain integration — drain manufacturer's bonded flange specification; (5) seating ledges / niches — extend tanking 100mm beyond tile finish into substrate; (6) windows in shower zone — full-height tanking + sealed reveal + non-corroding window frame (avoid timber). Manufacturer-specific systems: BAL Tank-It + BAL Single-Part Flexible Adhesive + BAL Microflex Grout = 25-year system warranty when fitted by BAL-certified tiler. Heritage / Listed Building: timber suspended floor wet room install premium — strengthen joists, install cement-board over plywood, manage floor build-up against existing finishes; LBC required for any visible modification. Wet room over flat below: install at first-fix with surveyor sign-off; insurance disclosure; leasehold consent; flood detector + automatic shut-off (Sentry Box, LeakSmart) £450–£950 retrofit.
