Wetrooms have become a popular choice for bathrooms. They are a striking and spacious option for any size room and the sense of open space that they provide ensures that occupants feel comfortable and indulged.

Plus, wet rooms are easy to clean, making them an even more attractive option to homeowners. Alongside comprehensive wet room design and tanking solutions, Marmox manufacture and supply the pre-formed sloping shower bases, the sloping boards, the tile backer boards, the drains and waterproofing materials needed to create modern, barrier-free tiled wet-rooms and level-access shower areas. Marmox wet room tanking products and materials also come with a lifetime guarantee.

Leak-proof wet-rooms can now be safely constructed in any room of a property with the confidence that they come with Marmox’s lifetime guarantee so there will be no risk of leaks. This warranty is given by virtue of the simplicity of the design. The core material of the wet room bathroom boards and sloping shower floor former (the Showerlay) is extruded polystyrene which by its very nature simply cannot allow moisture to pass through it, the drain which is supplied is designed to simply screw into position so again there is no possibility of leaks and other joints are sealed with Marmox’s waterproofing, tanking materials.

How to make a tiled wetroom

Undertaking a wetroom requires a variety of specialist techniques and years of experience. The sloping part of a tiled wet room is made using a Marmox Showerlay. A Showerlay provides the slope to the drain and needs to be in the area where the shower head is. The surrounding floor is normally flat and comprises (flat) Marmox Multiboard of the same thickness as the Showerlay. Multiboard and the Showerlay are 100% waterproof. They also provide a decoupling layer which will absorb minor expansions and contractions in the sub-floor thereby reducing the likelihood of the grout and the tiles moving or cracking.

On wooden floor

Showerlays can be used on a concrete floor or a wooden floor. On a wooden floor they can either be laid onto the exiting floor in which case they will be 20mm, + square drain or 40mm, + linear drain (or 24mm is using the larger square drain versions) higher than the rest of the floor OR they can be dropped into the wet room floor by removing the floorboards so they sit on top of the joists (but they do need completely supporting so a “shelf” would need to be constructed between the joists so that the Showerlay is sitting not just on the joists but on a completely flat surface).

If laid on top of the existing floor, the 20mm thick versions will be proud of the existing floor level by 20mm therefore 20mm Marmox Multiboard can be used to cover (and waterproof and insulate) the rest of the floor giving an even coverage. If a 20mm thick Showerlay is sunk down to joist level then (including the layer of tile adhesive) it would only be proud of the rest of the floor by between about 4 to 6mm. 40mm thick showerlays are usually fitted at joist level and these would be approximately 20mm higher than the rest of the floor so the rest of the floor is then covered with 20mm Multiboard.


On concrete floor

On concrete floors there are three common methods of installing wet room tanking products such as the Showerlay.

  1. To provide the same levels of insulation and improved tile stability Marmox multiboard of the same thickness of the Showerlay is simply laid on the surrounding floor next to the Showerlay.
  2. Where thermal insulation is not important, it is common to lay the Showerlay on the concrete and then screed up to it.
  3. When the floor cannot be excavated to bury the drain (such as in a flat or apartment) it is necessary to use the Showerlay as a raised shower – for this circumstance we manufacture a 100mm high “plinth” that goes on the floor underneath the Showerlay and allows the drain gulley to sit in the cavity just above the level of the floor.

Waterproofing the joints

Marmox Showerlay and Multiboard are completely impermeable to water however the joints especially around the wetroom showering area need to be sealed. Seal adjoining boards together with the sealant, Marmox Multibond and use Marmox self-adhesive waterproof tape over the joints in in areas that will get especially wet or be prone to standing water. Sometimes, it will be decided to not cover the surrounding wooden floor with waterproof Marmox multiboard and on such occasions, the rest of the floor needs to be water-proofed with a waterproof membrane; this should overlap the Showelay by about 5cm to provide a waterproof seal. The edges of the Showerlay and the area directly around it must be water tight. The tape will ensure the wet room will not leak even if water passes through the grout.

The walls

Applying Marmox Multiboards to walls provides the perfect surface to tile upon. Because the boards are inert to temperature, moisture and absorb the tiny movements in the house, tile backer boards ensure the tiles remain stable and secure. Tiled walls in bathrooms – especially external walls are prone to condensation; cladding them with Marmox Multiboard will significantly reduce this. It is recommended that all the walls in a wet room should be lined with Marmox prior to tiling. 10mm or 12.5mm thick board is commonly used for this.

What is used to fix Showerlay to floors?

Showerlays should be fixed to the floor using a C2 tile adhesive (that is a powder based tile adhesive). Always use a tile adhesive that is made up from powder and not an already made-up one in a bucket since moisture can cause these to break down during use.

Tile adhesive is the best method but will raise the wet room's floor level by 2 to 3mm. 

It is important to ensure an even layer of tile adhesive under the Showerlay is used. Pay special attention to ensuring good coverage around the drain area because it needs to be fully secured there. If there are any areas where the base of the Showerlay is not fixed firmly, the product will feel ‘springy’ and the tiles will be less secure.

Can Showerlays be cut to size?

Yes, the Showerlays can be easily trimmed using either a Stanley knife or a hack saw. The slope of these boards is constant over the whole surface so cutting off the outside 100mm, 200mm or corner for a soil stack will not make the board any less sloped.

Be aware, however, that cutting off more than 100mm will result in that cut perimeter edge being thinner so this edge with a reduced thickness must face the wall rather than surrounding floor.

The only part of the linear showerlays that can be easily trimmed is the area opposite to where the linear channel is. These units cannot generally be made thinner – for example, the 1200mm x 900mm has the drain parallel to the 1200mm long side – this length must always be 1200mm.


Using Marmox Multiboard will improve the thermal insulation of the wet room however one of the consequences of having a warmer air temperature is that warmer air can hold more moisture. It is therefore necessary to ensure there is adequate ventilation. This advice is actually important – any insulation will increase the risk of condensation so do check the ventilation!

Electric Underfloor Heating

Using Marmox Multiboard and Showerlay will significantly improve the efficiency of electric UFH. Electric UFH can be fitted directly onto the board’s surface.


Alternative wetroom designs

An alternative is to fit a Marmox Decotray, our luxurious, imitation stone, formers with a non-slip surface. These stylish barrier-free sloping formers can be incorporated within a tiled floor as a direct replacement for a Showerlay.