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January 2025

 10 top installer questions answered - on waterproofing and/or tiling a bathroom, shower room or wet room

Last year sawSchlüter-Systemsopen a significantly upgraded training facility at the company's Coalville premises, featuring multiple room-sets and product rigs which offer attendees the chance to get hands-on with the diverse product lines. Here the manufacturer's highly experienced Training Manager, Andrew Curry, outlines ten top questions from installers.

Andrew Curry - Training Manager at Schlüter-Systems

Answering challenges around waterproofing

Schlüter-Systems runs training courses for installers throughout the year with a typical intake including tradespeople like tilers, general builders, plumbers and joiners; and all of them will have wide ranging questions regarding the suitability and benefits of different systems. Interestingly, because we offer such a diverse product range, installers tend to cherry-pick depending on their needs and personal preferences, but none will have ever encountered the whole spectrum of solutions.

Bathroom fitters might use the waterproofing membranes, the shower tray drain and underfloor heating systems but never encounter the systems for treating balconies and terraces. However, the more they diversify and learn, the greater the potential is for maximising their experience, and growing their business. The most obvious first question at the start of a session is: 

1. Why do we need waterproofing?

 We should consider waterproofing within bathrooms and other wet areas as being just as important as protecting the building envelope and sub-structure from water ingress, a situation which British Standards has emphasised in recent times: addressing the topic under BS 535 Part 1. In order for participants on the course to fully grasp the importance, we talk about the actual volume of water you are dealing with: contrasting indoor and outdoor conditions.

The average UK rainfall is six litres of water per square metreper daybut, in a shower area, the figure is close to 60 litres in justeight minutes, with the rate doubling where power showers are involved. Therefore, it is imperative to protect plasterboard and plywood or other vulnerable substrates from exposure, and ensure this deluge is efficiently directed to the wastewater drainage.   

And onwards -

2. Where are the specific areas which must be protected from water penetration?

The answer is distinctly different for a bathroom as opposed to a shower enclosure. Within a wetroom, the clue is very definitely in the name, with all surfaces and junctions needing to be considered. You would, in effect, tank the entire room. In a cubicle or larger shower enclosure, it is best practice to waterproof the entire floor area and the surrounding wall areas to a minimum height level with the shower head. For showers mounted above baths, it is again recommended to waterproof the full floor area and the wall area to a width of 1500mm as well as to a similar height.

The weakest points are the junctions between the wall tiling and the top of the bath or shower tray, for which Schlüter-Systems offers a special profile known asKERDI-TSwhich makes a robust seal. The KERDI-TS profiles are available as kits to suit bathtubs and shower trays as well as other units; all of which will be fitted before the main installation takes place.  

3. What is the difference between waterproof and water resistant?

While some manufacturers use misleading terminology, waterproof refers to a material or surface that is completely impervious to water, whereas water resisting materials are porous, which means they will absorb moisture, though remaining unaffected themselves. Water resistant plasterboard typically requires a separate waterproofing layer to stop water tracking down the back to affect battens or even the floorboards and other susceptible substrates.

4. Why would you choose KERDI as opposed to DITRA for waterproofing?

KERDI membrane - at just 0.5mm thick - and KERDI-BOARDS are generally used to protect wall areas, while the latter offers thermal insulating and other benefits. Where a water-resistant board has been laid across floors for structural reasons, DITRA would normally be preferred for waterproofing as its 3mm thick structure featuring cavities offers uncoupling properties to accommodate relative thermal or other movement. When correctly installed, though, both DITRA and KERDI systems create completely waterproof backgrounds, and total peace of mind.

5.Can DITRA be used straight over existing boards?

Yes, provided the existing substrate is rigid and load bearing - "deflection free" being the main criteria. DITRA can prevent timber getting wet, because, without adequate waterproofing, timber will expand and contract leading to grout cracking and water ingress. DITRA is the tried and tested answer, proven for almost four decades in use. 

6. If I wanted to install underfloor heating with DITRA, is it laid above or below the actual matting?

Ideally, you want DITRA sitting as close to the tiling as possible to protect the ceramics against any movement, but this is whyDITRA HEATwas developed: to provide an uncoupling system, with waterproofing and heat source all installed in one operation. This integrated product solution cuts installation time and improves heating output performance. In fact, an electric UFH system is the most cost-effective solution for wet areas - cheaper to install and offering comfort underfoot, quickly warming up when required.

7. How do you fixKERDI-200polyethylene membrane for bonded waterproofing assemblies offering a water vapour retardant value of Sd = 5.15 m?

A cement-based tile adhesive of min classification C2 should be spread using a 3x3 or 4x4 mm notched trowel, and the membrane rolled into place. Most installers would use a rapid setting adhesive, normally with a setting time of a couple of hours, so that they can lay the tiles as quickly as possible. Ready mixed adhesives are to be avoided as they would never set because they cannot dry out behind the membrane.

8.Can I use tile adhesive to effectively joint KERDI?

When using either KERDI,orKERDI-BOARD, it is crucial to correctly joint the overlaps; and, unfortunately, tile cement - as with grout - simply does not offer the necessary waterproof performance.  The safest and best solution is to employ the SchlüterKERDI-KEBAsealer band and two-partKERDI-COLLadhesive.  

9. How easy areSchlüter's Peel & Stickproducts to reposition, and how much pressure is required to actually bondthem in place once the installer is happy with the alignment?   

Peel & Stick is an important part of the range for small builders and others less experienced at tiling work. One of the key advantages of this novel product solution is the ability to realign it if, say, it is initially not square with the room. However, the user must avoid applying pressure prematurely. 

Once the tradesperson is confident in their positioning, the adhesive surface'sgrabis initiated by applying firm pressure with a trowel or roller, after which the membrane cannot be lifted again. Peel & Stick is continuing to open up new market opportunities forSchlüterparticularly where the customer is concerned about tackling timber floors. 

Basically, Peel & Stick simplifies the logistics of getting everything needed to the work area, especially on upper floors, and avoids the problems associated with timber's sensitivity to moisture. The ready-to-lay membrane is also ideally suited to overlaying P5, as long as it is stable and deflection free. Cement-based tile adhesive simply does not offer long-term performance in such situations.   

10.Where would you use KERDI instead of KERDI-BOARD?

KERDI was developed to be laid over existing substrates, such as plasterboard and also moisture resisting plasterboard. It is used to create waterproof backgrounds, saving both time and cost when creating wetrooms.  Available in a range of thicknesses, KERDI-BOARD provides the same dependable waterproofing performance, but is utilised as a tilebacker or for the creation countertops and other fitted units amongst other applications.   

For further information, call01530 813396or visithttps://www.schluter.co.uk/

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