Guide 5 – Wetroom Tanking, Under Floor Heating & Tiling options

Tanking a Wetroom

Why do you need to tank a wetroom?  

No matter how good the tiling and grouting is, movement and different thermal expansion can cause the finest of cracks that lets water track through to your floor or walls.   For these reasons British Standard BS5385 Part 4 stipulated that all tiling in wet areas should have a fully sealed, waterproof membrane under them.

Underlay (non-structural) wetroom formers need to be tanked over 300mm from the edges but Maxxus (structural) decks need tanking over the entire deck and over in to the throat of the drain.


The Wetroom Innovations liquid tanking system.

Tanking systems

This can be done using a sheet membrane with sealed joints or more easily with a tanking compound where all corners and joints between substrates are reinforced.  All our liquid tanking kits are supplied with the primer, compound, joint tape and corners to complete the average wetroom (10m2). To tank larger or more complex areas additional items are available.

How to tank a Wetroom – with tanking compound

Full instructions are supplied with each kit. For the “Life of tiling warranty”, the instructions should be followed carefully. This is a quick guide so you can see how easy this part of the job can be.

First the floor, wetroom deck and walls should be secure and in good condition.  The area that will be classed as the wet area should be determined and then at least an additional 300mm added.  The whole room can be tanked but it is only absolutely necessary to tank the area that will be subject to a flow or splashing of water.

Any areas that are porous or previously painted  e.g. plaster, plaster board and timber  should be primed (A one litre bottle is supplied with each kit).  Uneven or unstable walls can be overlaid with Tile Backer Board.

All joints and corners need reinforcing using the special tape and preformed corners. These are stuck in place using the tanking compound and have to well pushed down to ensure good adhesion.

Tanking wetroom with liquid tanking compound

The rest of the area can then have its first coat of the membrane. This can be applied with a brush or roller. Apply the membrane compound in one direction, across the floor and vertically at least one meter up the walls.

Depending on conditions the compound should be ready for a second coat after 3 – 4 hrs.  The second coat should be applied at 90 degrees to the first.  The two thin coats at right angles give the even, reliable and impervious layer you can be confident to tile over.


Under floor heating in a Wet Room

Under floor heating give the added luxury of a warm floor it also helps rapid drying of the floor after showering and can eliminate the need for a radiator in the room.

An under tile heating mat is laid directly on to the tanked floor.  With a thickness of just 3mm the mat is easily tiled over using powder tile adhesive or screeded over with latex self-levelling compound.

underfloor heating

The single cable from the mat should be chased up a wall in a dry area where the connection to the controller unit and appropriate mains supply can be made.

Tiling a Wetroom

To complete the wetroom aesthetically, tiling is the finishing touch. Some designs use different tiles to designate the shower area others use a continuous scheme throughout the whole room.  A Wetroom kit is suitable for all types and sizes of tile including mosaic tiles. (note: 25mm square minimum size mosaic tiles on underlay formers and tile backer board.)

Mosaic tiles up to 40mm square will drape in to the former shape without tile cuts. For larger tiles, plan out how the tiles and patterns will work.  This is particularly important with larger tiles to get grout lines well matched on the floor and walls. Take in to consideration how the tiles may need to be cut to fit the angles where the slopes of the deck meet and the position of the drain.

tiling a wetroom

All tanking /waterproofing product are available from the DIYwetroom store


Guide 1 – Wetroom Design Planner

Inspiration and Ideas for creative wetroom planning including the downloadable planner sheets.

Typical spray pattern area from a wetroom shower

Guide 2 – Wetroom Floors and Drainage

What you need to know to plan your floor and drainage.

full supports of floor under wetroom deck

Guide 3 – Wetroom Kit Installation

Overview of how to install a wetroom kit on various types of floors.

maximum pipe lengths for wetroom drainage

Guide 4 – Tips on Drains and Waste Installation for Wetrooms

A few tips to help you plan how the waste pipe can be routed and connected.

Tanking wetroom with liquid tanking compound

Guide 5 – Wetroom Tanking, Under Floor Heating & Tiling options

How to tank / waterproof a wetroom using the Wetroom Innovations liquid tanking compound.