What needs to be waterproofed in a bathroom?

With any luck your build team will know what's needed here, but it's helpful to know what to expect in advance - especially if you need to check it's included in your quote!

Tiles, grout or wall panels are the visible finish in a bathroom. Waterproofing sits behind them, and that is what protects the structure of your home should the tile / grouting fail.

It's pretty common in older properties to find there wasn't any waterproofing behind the tiles, and not to have had a problem, however it is best practice and building regulations in the UK do recommend waterproofing / tanking to avoid any problems should tiling, grouts or joins fail over time. Side note - Australian regulations mandate waterproofing.

If grout, tiles or joins fail over time, without a waterproofing layer behind them, water will eventually damage walls, floors and ceilings - expensive things to fix.

Waterproofing, often called tanking, is the layer that stops water getting into the structure of the building.

• A waterproof membrane or coating applied to walls and floors
• Sealing joints, corners and where pipework passes through the wall
• Preparing surfaces before tiles go on

Your tiling sits on top of the waterproofing layer. Without it, water can pass through grout lines and small gaps over time.

This is also one of those things that varies depending on where you are in the world.

• In the UK, bathrooms are often waterproofed just around the main wet areas
• Meanwhile in Australia, full bathroom floor waterproofing is much more common and in many situations mandatory - on upper floors and timber floor constructions

You don't have to waterproof every surface in a bathroom, but you do in certain areas:

In wet areas like the shower, you want to waterproof:

• All walls within the shower up to shower head height
• Around valves, pipe outlets and fittings where pipework passes through the wall
• The joint between shower tray and wall needs to be sealed properly, however the shower tray itself is a waterproof layer already
• Shower niche? You want to make sure that's well sealed too

A wet room changes the approach completely. Instead of just protecting specific areas, the whole floor becomes part of the shower.

• The floor should be fully waterproofed before tiling, (and also slope towards a drain)
• Walls within the main wet area protected up to head height
• Lower wall areas should also be protected

This requires more planning and a different floor build-up.

If you have a shower over the bath, or the bath sits against a wall:

• The surfaces around the bath need waterproofing
• The joint between bath and wall needs to be sealed properly

The surfaces behind the basin need waterproofing - it can get pretty wet there too.

Not every bathroom floor is fully tanked, but it depends on the setup.

• Wet rooms always require full floor waterproofing
• Timber floors often benefit from additional protection
• Concrete floors are porous so will still need protection

Waterproofing is not something that gets decided at the end.

If you are changing the room layout or still to decide on a wet room vs. enclosed shower tray, these decisions need to be made early, at least in time for your first fix so that the right approach to waterproofing is applied.

Arguably you really want to have your layout locked down as much as possible before quoting anyway, so that the quotes are as accurate as they can be!

It affects:

• Floor levels and build-up
• Drain positioning
• Wall construction
• The order of work on site

A common mistake would be assuming your tiles are themselves waterproof. In reality, grout lines and joins allow moisture through over time, which is why the waterproofing behind matters.