Wetrooms of old have a bad reputation. The products available and methods for installing wetrooms have, however, moved on considerably in the last decade or so. Installed in the correct way, a wetroom with that seamless line of tiles without a shower tray can look stunning — and more importantly, be leak-free. Done in the wrong way, not only can the work look substandard but can lead to repair work, potentially costing thousands.

The buzz word is ‘tanking’. This is where a waterproof seal is created over the subfloor and any adjacent walls so that if any water does find its way through, it sits within this layer rather than leaking through to the ceiling and room below. 

But this is a backup option. You should still make sure the work is carried out properly (with walls and subfloors thoroughly prepared) and not simply rely on the fact that there is tanking in place.

You should install the wetroom as if nothing was there behind it: this means ensuring the work is carried out well. Years ago, tiles were laid on sand and cement with nothing else. It goes to prove, if the work is carried out properly then that backup tanking layer really is there as a last resort. 

pulling up floorboards to prep for installing a wetroom

When the existing bathroom floor is removed, the condition of the subfloor should be assessed — and replaced where it is not fit for purpose

Removing Existing Sanitaryware

When removing the existing bath/shower suite, all your water outlets should be turned off. Typically there should be valves cut into the pipework that supplies the hot and cold feeds to the sanitaryware. These simply need turning off so that you can remove the items without water going everywhere. However, you will more than likely need to turn the water off to remove the shower valve if it is surface-mounted or chased into the wall.

When the floor covering (tiles, vinyl, etc.) is removed, it is worth closely inspecting the existing subfloor.

For suspended floors, this subfloor may be:

  • ply
  • chipboard
  • OSB
  • floorboards

The quality of the existing subfloor will determine if it needs replacing. Remember your finished floor – and wetroom – will only be as good as the subfloor beneath it.

Using a spirit level to make sure the floor is level

Ensuring the floor is level is key when installing a wetroom. Packers can be used to level out the floor

Preparing the Subfloor, and First Fix Work

One of the most important things when prepping a wetroom is to ensure the floor is level. If you have ripped out the subfloor, you can cut packers/firings or blocks to bring the low spots up to create a level floor. You will then lay your new subfloor on top of this.

If there is any ‘bounce’ in the timber floor you will need to strengthen the floor, either with noggins or doubling up on the floor joists (especially if they are old and thin). Ideally you should introduce a good quality marine ply on top of the floor joists.

However, you can be looking at £70-£80 (excluding VAT) for a 8x4ft sheet. This can soon add up on a big floor. There are alternatives, but do not go with the budget options as the layers can separate. You could also use a ¾ green chipboard.

use noggins to help strengthen old floor joists

Noggins can be introduced to help strengthen old floor joists

Another option, which is again expensive but very good, is a cement board. If you’re not ripping up the existing subfloor, you can use a self-levelling compound. This usually comes in 20 or 25kg bags that you mix with approximately 5 litres of water. (Always check the bag as different manufacturers will provide different guidelines.)

It is vital that you don’t add extra water to try and get the compound to go further; this will result in it not mixing correctly and becoming watery in areas.

If your existing floor is level but has an inferior wood quality, such as floorboards, anti-fracture matting or a decoupling membrane can be used to pull the whole subfloor together. One product I have used many times is Schlüter®-DITRA. As it’s a high-end product, it’s not particularly cheap but does save you money as you won’t have to rip up your existing subfloor and replace it.

Also, if you’re tiling the floor (regardless of whether you have a timber or concrete subfloor), then you should be using a decoupling membrane; it will absorb any floor movement, thus preventing the tiles laid on top breaking and/or cracking.

(MORE: Bathroom Flooring: What Material Should I Choose?)

first fix electrics and plumbing for wetroom

First fix plumbing and electrics can be undertaken while the subfloor is up

While the subfloor is up, this is the stage to install your pipes and cables as part of first fix electrics and plumbing. You’ll then be ready to install a wetroom tray (wetroom floor former) if using one. They’re great as they can be tanked and tiled over, but provide a fall to allow water to drain towards the drainage outlet.

Alternatively, products such as Unidrain can be installed against the wall, thus only requiring one slope to be created. “The gradient of slope is another factor that must be considered; we advise a gradient of 1.25-2%,” advises Birgitte Arendsdorf Olsen of Unidrain, for UK contact Wetroom Materials.

Top Tip

When the walls and ceiling of your bathroom or wetroom are plastered, if you have already put down your subfloor, make sure you cover it up as you don’t want this covered in bonding and plaster.

(MORE: Plastering Walls)

concrete board is attached against new studwalling

The walls may also need to be assessed. Here, a concrete board is installed against new studwalling

Tanking Your Wetroom

Nowadays, there are a number of different options for tanking your wetroom. In basic terms, there are paint or roll-on liquid solutions or membranes (which are generally self-adhesive), which can be used on the floor and walls.

These products are often provided as complete kits, which typically include a primer, tape (to seal corner and junctures between walls and floors) and the tanking layer. Whichever system you, your builder or your bathroom installer opts for, ensure you follow the manufacturer’s instructions very carefully as these can vary considerably.

preformed wetroom tray installed

A preformed wetroom tray has been installed here — these trays incorporate a fall towards the drainage

Your subfloor will have a bearing on the product you use. With concrete floors, you only typically need a thin membrane to prevent any leaks; these are generally thin self-adhesive products. For timber floors, a thicker membrane is required to prevent leaks and incorporate decoupling properties. These too are self-adhesive so you can start tiling as soon as you finish laying it.

Before applying a tanking layer, you need to ensure the wetroom area is clean, dry and dust free. You will then prime the whole area. Next you should apply the reinforcing tape over all joints, the corners of the walls, around the drain and where the floor meets the walls. Then the tanking layer can finally be applied.

corners and junctions have been taped and a tanking membrane installed

Here, marine ply has been abutted against the preformed wetroom tray. Then the corners and junctures have been taped and a tanking membrane installed

Sealing Stone Tiles 

It is worth bearing in mind that natural stone needs sealing. I find it is best to put one coat on before you start laying the tiles. This will help prevent a lot of adhesive being absorbed into the tiles. As you lay them, clean them as you go. Then, when all the tiles are laid, give them a clean and seal with another coat or two. This is vital because if you don’t do this before grouting, some grout will inevitably ‘bleed’ into the stone tiles and the finished floor will look awful. Once grouted, you can then give them a final clean and, depending on manufacturer, one final coat of seal.


Once the tanking layer has been installed and has fully dried out (in the case of rollon/paint-on solutions), you can begin tiling.

It is worth taking advice from your tile supplier as to what adhesive they recommend. Don’t just grab the first one you see or the cheapest; there will be a specific adhesive and grout for the type of tiles you are using, the subfloor, etc. For example, a different adhesive will be needed for natural stone tiles as compared to porcelain tiles and ceramic tiles. Seek advice from an experienced stockist.

Our Sponsors