Not only does 2025 mark the 25th anniversary of Harry Parsons setting up Marmox UK Ltd, but it will also remind many longer-serving bathroom and wetroom specialists of when the manufacturer’s remarkable Multiboard product first became available to the home market—providing them with a totally waterproof, insulating tilebacker board that completely eclipsed the performance of conventional plasterboard.
The fact that it took almost a quarter-century for the NHBC to tighten its regulations on the unsuitability of certain substrates in these settings will also be a matter of frustration for the countless homebuyers who have suffered the inconvenience and expense of needing to have the walls—and often the floor structure—around baths and showers reinstated due to water penetration and consequential damage. In addition to gypsum plasterboard, the guidance also effectively discourages specifiers from utilising magnesium oxide boards, which have shown a tendency to suffer moisture-related failures.
For those who have yet to hear about the country’s leading warranty provider’s introduction of tough new guidelines to prevent such water damage, we should outline the main content of NHBC 9.2/06, which came into force on January 1st this year. The document applies to all new homes registered with the NHBC, focusing on waterproofing details in bathrooms and other wetrooms.
It stresses the need for structural integrity in waterproofing solutions, with particular attention paid to areas around baths and shower enclosures. In wetrooms where the entire floor and surrounding walls are expected to be regularly wetted—and where power showers are installed—full tanking is required. In less arduous situations, such as with low-flow showers, waterproof adhesive and grout may be considered adequate, though specifiers should be mindful that fittings and flow rates may be increased by future occupants.
From the perspective of manufacturers such as Marmox—whose waterproof panels, shower formers, tapes and adhesives are now under renewed scrutiny—the onus is on them to prove that all system components perform together so water cannot penetrate beyond the line of defence. Supportive of the NHBC initiative, Marmox has now had further BBA testing, which confirms the modified concrete cement-coated XPS boards not only offer a stable background for direct tiling, but also fulfil the enhanced technical objectives of 9.2/06.
In relation to the NHBC Standards 2025, the certificate states:
“In the opinion of the BBA, Marmox Tilebacker Boards (referring to Multiboards), if installed, used and maintained in accordance with this certificate, can satisfy or contribute to satisfying the relevant requirements in relation to NHBC Standards Part 9 Finishes; Chapters 9.2 Wall and Ceiling Finishes and 9.3 Floor Finishes.”
The Technical Manager for Marmox, Mark Bowman, comments:
“Essentially, the new guidance means you have to prove your system is waterproof—not just the boards themselves—which, as Multiboard is a modified cement-faced extruded polystyrene, is a given. So, you have to offer a viable solution for the joints between them, which we do with Marmox Self-Adhesive Waterproof Tape and MSP 360 Sealant & Adhesive. The actual test conducted by the BBA saw a box—somewhat reminiscent of a Belfast sink—being built, and the prescribed volume of water poured into it to ensure it didn’t leak. That testing was completed on the 27th of February this year.”
“The BBA is the only test house authorised to carry out this testing in relation to the new NHBC guidance, and the fact that the joints were treated in the same way as any sheet of Multiboard installed when tanking a wetroom should give real confidence to specifiers, installers, and end users.”
Marmox is currently in the process of updating its selection of shower formers—rationalising the range of sizes, attaching a slightly different model of drain outlet, and featuring a section of membrane bonded onto the back to overlap with the rest of the boarding. The Marmox stand at this year’s Installer Live exhibition also saw the company showcasing new versions of its popular shower niches and other products that help contribute to a consistently constructed wetroom shell.