Bathroom Tanking: Why Waterproofing Comes Before Tiles

Tanking is a waterproof layer applied to the walls and floor of a shower or wet area before the tiles go on. Tiles shed most water, but grout and the joints between tiles are not fully waterproof, so without tanking water slowly gets behind them and into the wall or floor underneath.

It is one of the least visible parts of a bathroom, and one of the most important. Once the tiles are up you cannot see whether it was done, which is why it is worth asking about before the work starts.

Why tiles and grout are not enough

A glazed tile surface sheds water well. The weak points are everything around it:

• Grout is a cement or resin filler between tiles. Standard cement grout is porous and absorbs some moisture every time the shower runs.
• Hairline cracks can open in grout or adhesive as a house moves slightly over time.
• Corners, pipe holes and the joint where the tray or bath meets the wall move and flex more than flat wall, so they are the most common places for water to get through.

A shower runs every day, often more than once. Even a small amount of water getting through each time adds up over months and years, and standard plasterboard and timber do not cope well with being damp.

Where tanking is needed

• Shower enclosures: the walls inside the enclosure and the floor if it is a level-access or walk-in shower.
• Over-bath showers: the walls around the bath that get wet when the shower is used.
• Wet rooms: the whole floor and the lower part of the walls, with extra height in the showering area.
• Splash zones: behind basins and baths, where it is good practice in a busy family bathroom.

The main ways a bathroom is tanked

Liquid membrane systems

A primer goes on first, then a waterproof liquid is painted or rolled on in coats, with reinforcing tape bedded into the corners and joints. Each coat needs to dry before the next, and the whole system needs to cure before tiling. This suits most shower walls and floors.

Sheet membranes

Thin waterproof sheets are bonded to the wall or floor with adhesive, with the joints overlapped and sealed. They can be quicker to tile over and are often used on floors.

Waterproof backer boards

Instead of plasterboard, the walls are lined with boards made for wet areas. The joints and screw heads still need sealing with the manufacturer's tape and sealant, so the boards are part of a system rather than a fix on their own.

Whichever method is used, the important part is following the manufacturer's instructions all the way through: the right primer, every corner and pipe hole sealed, and the full drying times respected.

Signs a shower was not waterproofed properly

• Grout that stays dark long after the shower has been used.
• Tiles that sound hollow when tapped, or that move when pressed.
• Black mould coming back through the silicone again and again.
• Peeling paint, bubbling plaster or a damp smell in the room on the other side of the shower wall.
• Stains on the ceiling below the bathroom.

Some of these can be a simple failed silicone seal, which is a small repair. If the problem keeps coming back, it is usually because water is already behind the tiles, and the only proper fix is to strip the area and tank it before retiling. Our guide to how long a bathroom renovation takes explains where this fits in the order of work.

Does tanking add much time?

It adds a few days because of drying and curing times between coats and before tiling. That is time well spent. Retiling a shower after a leak costs far more than doing it properly first time, and leaks into the floor or the room below can turn into an insurance repair.

How ATR waterproofs a bathroom

On every bathroom renovation we tank wet areas properly before any tiling goes on, then tile, grout and seal. The tiling and finishing stage includes silicone sealing around baths, trays and basins and a snagging check before we sign the job off. Because we do not subcontract, the same team that tanks the room tiles it, so nothing gets missed between trades.

Shower leaking in Romford or Thurrock?

We work across Romford, Grays and the rest of Havering and Thurrock. If you have a shower that keeps leaking or you are planning a new bathroom, call 07795 673584 or ask for a free quote.