Ian Knifton of Schlüter-Systems discusses how best to approach a wetroom specification to ensure the correct design for a watertight finish
Wetrooms can be a great addition to both residential properties and those within the hospitality sector. Many homeowners consider this option to add value to their property, while hotel owners are realising the design potential a guest wetroom can bring. However, it is essential that the wetroom is properly fitted and watertight, using the right products and systems throughout the process.
Water-resistant vs waterproof
There is plenty of room for creativity in wetroom specification, but the designs need to be backed up with the correct materials and maintenance schedule in order to achieve the best results. This means understanding seemingly subtle details that in fact make all the difference, such as the distinctions between water-resistant and waterproof materials. This is a fundamental distinction to make in achieving a long-lasting result for a wetroom: water-resistant is partially absorbent; meaning water is able to reach the tiling background, whereas waterproof means totally impervious; that water is unable to reach the tiling background.
A common misconception is that tiles and grout are waterproof in themselves.
In fact, these two elements of an installation are at best, water-resistant. This means that for waterproofing protection, you must look at what is used beneath the tile covering.
Waterproofing for walls
There are three different options when it comes to choosing a waterproofing system for walls.
Commonly used liquid-applied membranes are cost-effective at the point of purchase. However, they can be difficult to apply evenly and slow-drying, often making them impractical for large-scale usage.
Sheet membranes provide uniform coverage and bridge cracks in substrates. Like liquid-applied membranes, their use relies on application to an even substrate. This means they are often used as a second layer over plasterboard or water-resistant backer boards.
Waterproof tile backer boards provide a flat and even substrate, as well as being ready waterproofed. Therefore, they can reduce the number of installation processes needed to create a waterproof assembly, which can save time and money onsite.
Waterproofing for floors
The same waterproofing systems used for walls are often not the best choice for floors. Floors endure more stresses, so extra functionality is desirable. An uncoupling membrane not only waterproofs but also helps to manage movement in the flooring assembly. This functionality is particularly important in heated floor assemblies, which expand and contract more than standard floors.
Tile & stone fixing
Tile and stone should always be fully bonded into the adhesive. ‘Dot and dab’ fixing techniques leave voids behind the tile, in which moisture can be harboured and mould can develop. Tile or stone greater than 12 mm in thickness should be mechanically fixed as per BS 8298.
A suitable substrate (e.g. plywood or blockwork) must be in place behind your chosen waterproofing in order to support this load.
Correct ‘falls to drainage’
Specifiers should accommodate falls to drainage in one area of the wetroom, unless the room is particularly small. Falls should be between 1:35 and 1:80 (i.e. for every
80 mm the incline travels towards the waste outlet, the floor level will fall 1 mm) as per BS 5385 Part 3. Falls should always be below the waterproofing layer, not in the tile adhesive applied above.
There are two main methods used to create falls. The traditional method involves using a screed formed to the required falls to drainage. The lowest point in the screed should still meet British Standards; if a screed is too thin, it will crack or crumble when under load.
The other option is to use a preformed shower board which is manufactured with the appropriate slope already created. Some also come ready-equipped with waterproofing layers.
Specifying a wetroom can be something of a juggling act; a client will likely have a strong opinion as to how it should look and tie in with the rest of a building and therefore focus can be drawn away from getting the fundamentals correct. However, if the factors listed above are taken into consideration, you can easily achieve a wetroom that not only looks great to suit the client’s needs, but also performs as it should, resulting in a long-lasting and beautiful installation.
Ian Knifton is head of technical and training at Schlüter-Systems