Domakihub How to Tank a Wet Room: Waterproofing Done Right
A step-by-step guide to wet room tanking that keeps water where it belongs.
Reviewed by Domakihub home & decor pros · 2026-06-23 · 5 min read
A wet room without proper tanking will leak — it is not a question of if but when. The video above walks through the full waterproofing process visually, while this guide breaks down each stage so you understand what your contractor is doing (or, for confident DIYers, what you need to do yourself). Whether you are retrofitting a bathroom in a holiday villa on Corfu or fitting out a new hotel ensuite in Athens, the principles are the same: water must be contained at the structure, not stopped by the tiles.
What Is Wet Room Tanking?
Tanking is the application of a continuous waterproof barrier — either a liquid membrane, a sheet membrane, or a combination of both — across every surface a wet room floor and wall can wet. Unlike a conventional shower tray, which relies on a single sealed unit, a wet room exposes the substrate directly to water spray and drainage flow. Tanking creates the watertight envelope that the tray would otherwise provide.
In Greece, most subfloors in apartments and villas are reinforced concrete, which is more forgiving than timber. Even so, movement cracks, plumbing penetrations, and floor-wall junctions are common failure points. A correctly tanked wet room can last 20 years; an incorrectly tanked one begins to fail within months.
When You Need a Professional (and When You May Not)
Tanking itself is not a licensed trade in Greece, but several surrounding tasks are. Any structural modification to the slab — cutting a drainage channel, lowering the floor level — requires a civil engineer and potentially a building permit (οικοδομική άδεια). Relocating or adding waste pipes involves a licensed plumber (υδραυλικός). If the wet room is in a multi-storey building, a structural engineer must confirm the slab can carry any additional screed weight before you begin.
The tanking membrane application itself is within a skilled DIYer's reach, but most property owners in Greece contract it to a tiler (πλακάς) experienced with wet rooms. A poor tanking job is invisible until it causes serious damp damage to the floor below — in a hotel or rental property, that risk justifies professional installation.
How to Tank a Wet Room: Step by Step
- 1
Prepare the Substrate
Strip any existing tiles, adhesive, and waterproof paint back to bare concrete or cement board. Fill all cracks, holes, and pipe penetrations with a flexible, waterproof filler or hydraulic cement. The surface must be sound, clean, dry, and free of dust or release agents. Any looseness or contamination will cause the membrane to delaminate. If the floor needs a fall (minimum 1:80 gradient toward the drain), lay a self-levelling or sand-cement screed at this stage and allow it to cure fully — typically 28 days for cement screed — before tanking.
- 2
Prime the Surfaces
Apply a dedicated tanking primer, diluted according to the manufacturer's instructions, to all surfaces that will receive the membrane. Priming improves adhesion and reveals any powdery or porous areas that need further preparation. Allow the primer to become touch-dry (usually 30–60 minutes) before moving on. In summer conditions in Greece, work in the early morning — high temperatures accelerate drying but can cause skinning before the primer penetrates properly.
- 3
Apply the First Coat of Liquid Membrane
Using a brush or roller, apply the liquid tanking membrane in a continuous coat to the entire floor and up the walls to at least 150 mm above the finished floor level. Pay close attention to corners and junctions: press a pre-cut strip of tanking tape or fabric reinforcement mesh into wet membrane at every floor-wall joint, every internal corner, and around the drain flange. These are the highest-risk points for leakage. Allow the first coat to cure to the touch before continuing.
- 4
Apply the Second (and Third) Coat
Apply a second full coat of liquid membrane perpendicular to the first to ensure even coverage. Most reputable systems (such as Mapei Mapelastic, Schluter Kerdi, or BAL Tanking Slurry) specify a minimum dry film thickness of 1–2 mm, which typically requires two to three coats. Check the coverage rate on the product data sheet and weigh out product accordingly — under-application is the most common cause of failure. Allow each coat to cure fully between applications.
- 5
Test Before Tiling
Before any tiles go on, perform a flood test: temporarily block the drain and fill the floor with 20–30 mm of water. Leave it for 24 hours and inspect the ceiling below, adjacent walls, and the drain perimeter for any signs of moisture. Only once the test passes should you proceed to tile adhesive and grout. Use a flexible, S1 or S2 class tile adhesive and epoxy or polyurethane grout rated for wet zones — standard cement grout is not sufficient in a fully wet room environment.
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FAQ
- Can I tank over existing tiles instead of removing them?
- In most cases, no. Liquid membranes require a sound, well-keyed substrate, and old tiles can harbour hollow spots, loose adhesive, and contamination. More importantly, adding membrane and new tiles on top of existing tiles raises floor level and can cause door-clearance problems and stress at the drain. Strip back to the bare substrate for a result you can trust.
- How long does a tanked wet room last before it needs redoing?
- A correctly tanked wet room using a quality membrane system should remain watertight for 15–25 years, provided the grout and silicone sealant joints are maintained. Sealant around the drain and at corners typically needs replacing every 5–8 years. If you notice grout cracking or tiles becoming hollow-sounding, investigate promptly — early intervention is far cheaper than re-tanking after water damage has spread.
- Do I need a building permit to install a wet room in Greece?
- Installing a wet room within an existing bathroom footprint, without structural changes, generally does not require a building permit in Greece. However, if you are altering the floor slab (e.g. cutting a channel for a linear drain), relocating drainage waste pipes, or changing room dimensions, you will need a licensed plumber and potentially a permit issued by the local planning authority (Δήμος). Always consult a licensed civil engineer (πολιτικός μηχανικός) before any structural work in an apartment building.