24   Maggio   2013

Low-thickness ceramic tiles and sheets

Research to support standardisation procedure conducted as part of the InProCer Project (Development Objective 5).

Introduction and preliminary characterisation
by Giorgio Timellini - Centro Ceramico Bologna

InProCer –Workshop for Ceramic Product and Process Innovation
Regione Emlia Romagna –Funding programme “From production districts to technological districts”

Thin ceramic tiles and sheets come in a variety of sizes, from the most widely-used and standard formats through to sizes of the order of metres (for example 3 metres). Thicknesses vary from 3 to 5-5.5 mm. Alongside tiles made solely of ceramic, other types of thin sheets or panels are available with a layer of different material and composition (for example a fibreglass mesh) applied to the back by means of special adhesives.
As building elements for covering floors and walls, ceramic tiles are essentially required to perform two functions. The first is a technical function, as a construction material designed, manufactured and installed to withstand mechanical, chemical, thermal and hygrometric stresses during use without suffering damage or loss of functionality. The second function is aesthetic and architectural as the tiles serve to create a functional and visually appealing interface between the built and natural environments.
From an aesthetic standpoint, thin tiles or sheets are clearly highly innovative and represent a major step forward with respect to conventional products. They are an innovation developed in Italy using new manufacturing techniques, also Italian.
From an architectural perspective, large format sheets provide an opportunity to design a surface with a drastic reduction in both the quantity of material used and the visual impact of the joints. In other words, the surface tiling consists of more ceramic and fewer grout joints, which is an advantage as the joints generally have lower resistance to ambient stresses and a greater tendency to trap organic and other materials originating from the environment and to host various kinds of microorganisms. This brings benefits in terms of technical characteristics and performance.
The smaller thickness also results in further advantages. Porcelain tile with a conventional thickness of around 10 mm has a weight per unit surface area in the region of 20 kg/m2, whereas a low-thickness panel weighs about half of this. This factor alone means that thin sheets qualify as products that make efficient use of resources. To cover 1 m2 of surface area, fewer raw materials need to be quarried and transported and a smaller mass of body and semi-finished products have to be processed, resulting in savings of fuel and water per m2 of tiled surface. Furthermore, a smaller mass of finished product per m2 needs to be transported from the place of manufacture to the point of sale and then the place of installation.
The lower weight and the other aspects we have mentioned bring two types of benefits. The first is strong performance in terms of sustainability, a very important goal for the building sector given the inclusion of sustainability amongst the basic requirements of buildings in the recent European Construction Products Regulation (EU Regulation No. 305/2011 – 9 March 2011) and the close relationship between sustainability and competitiveness. The current focus on sustainability is highlighted by the strong interest on the part of the various manufacturing sectors. In the case of Italian ceramic tiles, this has led to the growing diffusion of environmental product marks such as Ecolabel, while Technical Committee ISO TC 189 “Ceramic Tiles” has set up an Italian-led Working Group (WG7) with the task of developing an ISO standard on the sustainability of ceramic tiles and corresponding materials for tiling. In the case of composite panels with a layer applied to the back, the backing material must clearly be included in the relevant evaluation of sustainability.
Another aspect of interest regarding low-thickness and hence low-weight ceramic tiles is the growth in popularity of renovation and remodelling projects in the current critical period for the Italian and European building industry. One of the most interesting aspects of these projects is the possibility of installing new tiling on top of existing floor or wall coverings without removing the existing tiles, which results in a controlled increase in weight and thickness. As we will see in greater detail below, when doing this it is essential to adopt design procedures, techniques and installation materials that are specially developed for these tiles. 
From a technical standpoint, there are two key aspects, as demonstrated by the results presented below of a pre-standardisation sample survey conducted by Centro Ceramico as part of the InProCer OR5 project.
The first aspect is the role of tile thickness in breaking load. Breaking load is related to thickness by a quadratic function, so for example halving the tile thickness while maintaining the same format will reduce the breaking load by a factor of 4. Furthermore, because of its compact structure the material’s mechanical strength is not significantly different from that of conventional porcelain tile, with a modulus of rupture generally between 40 and 70 MPa. Water absorption is less than 0.5% and in many cases below 0.2%.
The second technical aspect of note is the greater flexibility of the sheet owing to its size and thickness. Once again, an extensive characteristic (bending of the sheet, as in the previous case of breaking load) depends essentially on the dimensions of the individual element and not on the material’s specific intensive mechanical properties. In particular, both conventional porcelain tiles and thin sheets or panels made of the same material generally have an elastic modulus of between 40 and 60 GPa.
Thin ceramic sheets should therefore be seen as elements capable of undergoing significant elastic deformation before breaking, whereas small format tiles – even with a small thickness and made of the same material as the large-format sheets – are rigid components that remain almost undeformed up to the point of breakage.
What are the consequences of these differences in properties between conventional tiles and low-thickness sheets or panels?
The smaller value of breaking load may be problematic, although this is generally only an issue when using thin sheets for tiling projects designed and carried through using conventional procedures and techniques. It is therefore essential to establish specific criteria and requirements for thin sheets, for the relevant installation materials and for the design and installation of thin tiling. This goal is pursued by the above-mentioned ISO TC 189 “Ceramic Tiles”, with the contribution of two working groups, WG4 and WG6.
The second consequence is that thin large-format sheets have such high levels of flexibility that they deform elastically even under their own weight alone. This places significant limitations on the techniques used for measuring tile properties, which are based on the assumption of substantial (or infinite) rigidity of the test specimen. Examples of measurements influenced by the flexibility of thin sheets are the measurements of flatness and modulus of rupture in bending, in which the test specimen is placed on point-like supports or blades, resulting in the risk of flexion. This flexion effectively alters the properties to be measured and makes the method unusable. For this reason alternative measurement methods that can be applied to thin tiles (ISO TC 189, WG1 “Test Methods” and WG4 “Thin Tiles”) are undergoing study, experimentation and development.

References
EU Regulation No. 305/2011 – 9 March 2011 (Construction Product Regulation, CPR)
Harmonised conditions for the marketing of construction products, replacing Council Directive 89/106/EEC

Ecolabel
ec.europa.eu/environment/ecolabel

ISO TC 189 “Ceramic Tiles”
WGI – Test methods – Convener A. Tenaglia
WG2 – Technical specifications – Convener E. Astrachan
WG4 - Thin tiles and panels – Convener L. Galassini
WG6 - Design and installation of ceramic tiling – Convener B. Newell
WG7 – Sustainability issues for ceramic tiling – Convener G. Timellini