Lightweight porcelain slabs: A quiet revolution in surface specification.
By Colin Stanyard Group Technical Manager Domus Group.
Over the past decade a quiet but highly significant revolution has taken place in the tile sector. The development of continuous compaction technology means that today’s leading manufacturers can offer massive porcelain slabs, up to 3,200 by 1,600mm and beyond, in a wide range of thicknesses.
These can be cut, prior to firing, into a large range of smaller formats meaning that specifiers can now create completely co-ordinated tiled interiors. New XXL porcelain slabs have re-defined the potential of tile. As well as traditional applications as a hard-wearing, easy-to-clean surface for walls and floors, porcelain slabs can be used for façades, worktops, countertops for reception areas, restaurant and bars, furniture, feature walls, and much more besides.
Continuous pressing production methods are completely integrated with the latest advances in decoration techniques, notably digital inkjet printing, sophisticated powder deposition, sinking inks and reactive pigments, allowing virtually limitless design options, including fully bespoke patterns and designs for one-off projects.
This design and engineering flexibility has been enhanced of late by the practice of designing colour and tone compatibility across diverse ranges. So, while it is now possible to get incredibly authentic reproductions of marble, limestone, concrete, and wood, it is also possible to mix different designs and finishes in the certain knowledge that they were created specifically to complement each other.
It is also possible to specify the pattern of, say, pulpis stone, but in a wide range of colours that are not found in the original stone, such as light grey, anthracite, or taupe. These can be paired with dramatically knotted wood-effect tiles in exactly the same tones, or contrasted with lighter or darker hues from the same colour family.
The thinner slab formats, between 3 to 10mm thick, have many specification benefits. They are significantly lighter in weight than their natural stone counterparts. Lightweight porcelain slabs have a clear weight advantage at 8 to 25kg per sq. metre. They can also be used to over-tile floors or walls, eliminating the need for striping out existing finishes in renovation projects, saving labour and logistics costs.
They also reduce material consumption which benefits the environment and plays into the green building agenda, as does the reduced energy required for manufacture.
Thinner formats are also easier to cut with a wet saw or even a standard hand-held glass cutter. Typically produced in 3,000 by 1,000mm slabs, they also bring all the aesthetic benefits of their thicker brothers.
But while it is easy to get carried away by just how large these ceramic slabs are, fundamentally, they still rely on the same basics – in terms of body preparation, pressing, and firing – as the smaller porcelain tiles with which architects are now so familiar.
Decoration on these unfired tiles can be achieved in many ways, and often one design is realised by a combination of different technologies working together. As well as though-body powder decoration, the main options are surface decoration technologies including rotary silk-screen printers, which are used to apply background dyes, a range of graphic designs, and protective surface glazes.
Today they are usually combined with digital ink-jet printers. These feature multiple print-head bars; with each bar able to carry a different colour pigment. The ink-jet printer operates like a plotter making repeated passes over the slab as required.
Digital decoration ensures high-resolution patterns or pictures. What’s more, there is no limit to the graphic designs possible, which opens the door to bespoke surface solutions.
Once decorated, the lightweight porcelain slabs are fired in gas or electric kilns for around 40 minutes at a temperature near 1,200°C. After firing, a carefully-controlled cooling phase ensures that the finished slabs are perfectly flat, exactly the right size and do not have internal stresses.
The end-result is a range of new surface materials that are taking ceramic ‘tiles’ into new application areas that were, quite simply, beyond reach only a decade or so ago. And this evolution continues, with today’s leading manufacturers developing ever more sophisticated ceramic surface solutions for the architectural projects of tomorrow.
Domus offers the largest collection of extra-large lightweight porcelain slabs in sizes up to 3.2 metres long and only 3 or 6mm thick. Light, versatile, and exceptionally durable, they incorporate cutting-edge inkjet ceramic and production technology.
Each slab is individually designed with rich authentic detail with options for book-matched pairs and ‘a chain’ of linked designs of up to six slabs. In addition, a bespoke cutting service utilising waterjet technology is available to create customised patterns and non-standard shapes and sizes. This is the future of ceramics, providing impressive design choice and superior technical performance.
New for 2019 is Prexious Magnum; a suite of elegant precious stones and luxury marble-effects. One of the stand-out designs is Alabastri Magnum, which comes in two colours, including one bright white colour option, and six sizes. This is a truly beautiful porcelain marble with a gloss polished finish. Versatile, strong, and scratch-resistant, it offers an accessible and reliable alternative to natural stone slabs.
Antique Marble Magnum, which comes in six colours, two finishes and two sizes authentically captures the timeless purity of this ancient, natural material. A combination of striking vein patterns and subtle markings combine to forge a classic look, in both natural and polished finishes.
Other designs in the Magnum collection include Ardoise Magnum in four stone-like colours and four sizes; Artwork Magnum, a contemporary terrazzo in an incredible 19 modern colours, three finishes and three sizes; the ever-popular Black & White Magnum in two finishes and eight sizes; and the minimalist but adaptable Build Pure Magnum, a minimal stone-effect in three natural colours, three finishes and four sizes.
Specifiers seeking elegant restraint will be drawn to Cover by Mutina, available in three colours and three sizes. In this option, the clay is blended with a mixture of micro-grit, which is then used as a base for the coloured patterns applied using the silk-screen method. These may be irregular, figurative or geometric.
Patricia Urquiola is just one of the outstanding designers who have created outstanding tile ranges for leading Italian manufacturer Mutina. Designers seeking the apotheosis of contemporary ceramic surfaces will find much to admire in Urquiola’s Mutina creations, including the sublime Dechirer XL in three colours, which takes porcelain textures to a new level.
Take the innovative Folded XL, created by Raw Edges for Mutina, this lightweight porcelain slab features a surface design moulded from the formations of folded paper. The effect is a subtly embossed, textured relief.
With a contemporary, minimal aesthetic, Foscer Slim is a stunning porcelain slab collection in an architectural palette comprised of natural and grey tones. At 6mm thick, Foscer Slim offers ultimate design flexibility in five large size formats up to 3,000 by 1,500mm, in both natural and bush hammered finishes.
To ensure that specifiers can find the exact finish to meet their design requirements, Domus’ portfolio also includes I Bianchi Magnum, I Classici Magnum, I Travertini Magnum, Industrial Magnum, La Roche Magnum, Limestone Slim, Materia Project Magnum, and Neutra 6.0 Magnum that tap into all of today’s leading surface trends.
For a touch of real opulence, Onyx Magnum, available in four colours and two sizes, is a high-end porcelain marble design inspired by natural onyx. The rich patterned aesthetic runs across all five shades, which range from bright white to deep grey and brown with strong-lined patterns throughout.
Another on-trend range is Rawtech Magnum. Here the two colour options, two finishes and four sizes bring great drama and personality to the industrial style with their high tonal variation and delicate markings. Above all, this range offers the distinguishing character of cement through surface ‘imperfections’ and a worn finish effect.
Storie by Cedit also has a care-worn look. Available in six colours and three sizes, it brings to mind the textures of faded frescos, stained plaster, and rust-stained masonry. Designed by Giorgia Zanellato and Daniele Bortotto for Cedit, this is a powerful yet flexible design statement.
Last, but by no means least, Veneziane Magnum is a distinctive porcelain collection influenced by traditional Venetian terrazzo, adding an artisanal feel to interior spaces. In a predominantly deep, rich palette, Veneziane Magnum is characterised by irregular flecked patterns which replicate composite material of marble chippings set into cement. A selection of matching mosaics and co-ordinating 10mm tiles complete the manifold design options.
The science of specification
Typically, for lightweight porcelain slab ranges, the pattern repeats every 6 to 40 slabs and this will depend on the design and the size of slab selected. Creating a random-effect requires the installer to select the correct slab design before fixing to ensure this effect.
Other impressive design options available, once the preserve of exclusive natural stone industry, includes repeating-patterns, book-matched pairs, and in-chain or in-series of up to six slabs that are designed to link together.
Thickness compatibility issues should be considered when slabs are mixed with other products to ensure surfaces are level and not stepped.
For floors that get wet, a non-slip natural or matt finish is recommended over a polished or semi-polished finish. However, to achieve a slip rating that achieves a higher (PTV) rating in the wet, specify a natural-grip finish or a matching 10mm thick tile with a suitable anti-slip finish.
In addition to a wide range of standard sizes on offer, a bespoke cut-to-size service is available for architects and designers utilising waterjet cutting that will create stunning and intricate large size shapes for a feature wall or floor.
Correct site handling and installation procedures for lightweight porcelain slabs are required to ensure an outstanding and hassle-free result. Due to the specialist nature of this material, it is essential that anyone intending to specify, handle or install it has a clear understanding of the product, its inherent characteristics, and the associated preparation and handling required to ensure a smooth and successful installation.
Take a typical Domus slab at 3,200 by 1,600mm, and 6 mm thick. The slab is large at 5.12 sq, metres, and, at 6mm thick, will weigh about 75kg. So while a thin slab is lighter per square metre than a traditional slab, it still requires three people or mechanical equipment to lift safely.
Size really does matter here. It is vital to ensure that there is sufficient access to the area on site to allow the specified size of slab to be safely and correctly carried to the position where they are to be installed. This is particularly important if the slabs have to be transported from the ground floor to higher levels.
At the installation point it is also essential that there is sufficient unobstructed working space available to safely cut, drill, apply adhesive and manoeuvre the slabs into their final position.
With these slabs, as well as ensuring contractors have the correct tools and equipment to properly cut, drill and achieve the required solid adhesive bed, handling of the slabs in a safe and time-efficient manner may well mean the use of a task-specific tile handling cradle or even a robotic machine capable of accurately lifting the slabs into place.
Specifiers also need to give careful consideration to the quantity of material required for each project, ensuring that sufficient additional material is ordered to allow for breakages and unforeseen damage on site.
Domus’ normal operating procedures means that materials up to 1,200 by 1,200mm are delivered boxed and on a pallet, while slabs over 1,200 by 1,200mm, and up to 3,200 by 1,600mm, are delivered in large wooden crates approximately 200mm larger than the slabs. Fork lift trucks with wide-spaced forks are required to lift these jumbo sized crates safely.
An extensive handling method statement is provided with each delivery. In general terms, however, it is vital that sufficient qualified labour is available to offload the materials, using either a lifting frame or quality suctions cups.
Sigma lifting and cutting solutions
Because Domus realises that safe, secure, and efficient site handling is now such a key component in a successful installation project, the company recommends the use of a Sigma Kera-Lift large format lifting frame. Kera-Lift is equipped with suction cups for lifting, handling, and laying slabs. Easily modifiable without the use of tools, with guides simply sliding to adjust to the length and width of slab being handled.
When cutting and handling Domus large format slabs, it is essential that appropriate PPE is worn, in particular gloves, glasses, and masks. Domus recommends the use of the Sigma Kera-Cut system, in conjunction with the lifting frame, to accurately and efficiently deliver both long linear cuts and angled cuts.
Drilling, fixing and adhesive options
Lightweight porcelain slabs can be drilled using diamond tip drill bits that are designed for porcelain tiles. Being thinner there is less to cut through.
All tiling work using Domus Magnum lightweight porcelain slabs should be carried out in accordance with BS 5385 and BS 8000. Only an approved, competent tiling contractor, with experience of similar projects, should be employed.
The single most important aspect for the correct installation of lightweight porcelain slabs to floors and walls is that a solid bed of adhesive is provided under each slab with no voids.
In addition to the walls and floors, a solid bed of adhesive should be applied to the back of each slab. The techniques adopted to achieve this are clearly detailed in the British Standard codes of practice and Domus fixing recommendations.
Domus recommends use of the Raimondi Levelling System to ensure that the slabs are level, flat, and an even joint spacing is achieved.
Movement Joints should be positioned in accordance with BS 5385 Part 1 Clause 6.5
Regarding grouting, Domus recommends Mapei’s Ultracolor Plus quick-setting grout for general areas. For food preparation areas, Mapei Kerapoxy Design or Kerapoxy CQ impervious and chemically resistant epoxy grout should be used.
For showers, Domus suggests Mapei’s Ultracolor Plus quick-setting grout. This formulation is high-performance, anti-efflorescence, mould-repellent, and water-repellent.
Perfect preparation for perfect results
High quality tiling with lightweight porcelain slabs requires precision. It is essential that the surface to receive tiling is as flat as possible.
For walls; the wall construction must be such that there is no deflection or very little deflection maximum 1/500 across the span in the walls. Domus recommends the use of cementitious backing boards, such as 12.5mm Knauf Aquapanel. Fixings should be provided at 150mm centres along studwork and at 200mm centres along any other additional bracing.
As detailed in the latest British Standard (BS 5385-1:2018, clause 126.96.36.199), plywood and other wood-based sheets or boards are not suitable for direct fixing. Where such boards are present they should be removed or over-boarded with a suitable tilebacker board, such as Schluter Kerdi Board or Wedi Building Board.
Sand:cement rendered walls should be fully cured and dry. They must also have adequate cohesive strength and be perfectly flat. Adjustments to the flatness may be achieved through an application of a suitable product from the Mapei Planitop range. It is essential that the wall substrates are rigid and that a maximum deflection of 1/500 across the span is not exceeded.
For floors: it is recommended that screeded floors should be prepared to SR1 +/- 3mm (or better) over a 2 metre straight edge. The maximum deviation for the installation of large format porcelain slabs should be 1mm over a 2 metre straight edge. Therefore, in almost every installation, a levelling compound – such as Mapei Ultraplan Renovation Screed 3240 – will be required, after first priming the screed with Mapei Eco Prim T. If this is not provided there is potential for voids occurring below the slabs, which could result in cracking or the failure of the installation.
On timber floors, to ensure a stable and solid base to receive porcelain slabs, Domus recommends the use of Knauf flooring products as a substrate for tiling, with Knauf Gifa recommended as the overlay board onto existing raised flooring or as a screed replacement system on pedestals. Knauf GIFAfloor is available in various thicknesses to suit all floor loading situations and is ideal as a substrate to receive Domus slabs.
Wet areas and underfloor heating
If the slabs are to be installed in wet or moisture laden areas, then a waterproof membrane should be applied to the backgrounds prior to the application of the slabs. Domus suggests that in continuously wet areas, plasterboard is substituted by cement boards, or other appropriate tilebacker boards, to provide a more effective background. Mapei Mapelastic Aquadefense waterproof membrane should be applied to the surface, with Mapeband tape to all junctions and outlets.
The installation recommendation for lightweight porcelain products over heated floors is the same as any other porcelain floor. It is essential that heated floor screeds are allowed to dry for 3 weeks and then the floor should be brought to its intended surface temperature for 3 days. It should then be allowed to cool to room temperature before any fixing is undertaken. Once the tiles are installed, the floor must be allowed to dry completely for a period of 10 days. After this period, the heat should be introduced at a rate of 5°C per day up to a maximum surface temperature of 30°C.
Established in 1964, Domus is the leading specification service and supplier of ceramic and porcelain tiles, mosaics, slabs, and engineered flooring products for both commercial and residential projects. A bespoke waterjet cutting service is available for cut-to-size slabs and custom designed walls or floors.
For over 50 years, Domus has been providing expert advice and technical solutions for all types of applications for the workplace or home. A comprehensive sampling and specification showroom service is available for professional designers and private clients.
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