Background ‘Artificial stone’ products used in the ceramic and building sector are currently obtained by mixing crushed-stone aggregate with a polymeric bonding agent (polyester) at a controlled temperature. It is an attractive product because it can be made more cheaply and more uniform than natural stone. Furthermore, it can be cast near the place of eventual use, meaning that the costs of transporting very large pieces of stone can be avoided. However, their production has several negative environmental aspects, including: A high consumption of thermal and electric energy, raw materials and water; The generation of substantial quantities of solid waste, including sludge containing high concentrations of toxic chemicals harmful to health; The emission of large quantities of pollution to the atmosphere, including CO2 and fine particles.Objectives The aim of the ReLiStoP project was to reduce pollution by completely avoiding the use of polyester resins, volatile solvents and hazardous pigments in the production of ‘artificial stone’ decoration. The project sought to obtain a more environmentally friendly product through the cold-casting of a composition of crushed-stone aggregate and a hydraulic binder. The process would involve hardening in purpose-built, humidity-controlled chambers at temperatures under 35°C. It was expected that this process would reduce energy consumption and avoid the use of hazardous toxic substances. It was also hoped that the resulting product would have higher physical resistance and require only a minimum of the finishing and trimming that currently produces high volumes of waste that can be neither recycled nor re-used. Results The ReLiStoP project successfully designed a new process to manufacture ceramic pieces of "artificial stone" without the use of polyester resins, volatile solvents or hazardous pigments. The process was demonstrated using a prototype where all tiles manufactured proved equivalent characteristics to the ones produced via traditional systems. Initial trials of the process found that the planned large and complex plant could be simplified and some planned steps were eliminated from the design, including little finishing and trimming processes. At the same time, the crisis experienced in the European construction sector also required a scaling-back of planned investment; the existing production line even had to be closed. Yet, this also provided an opportunity as some of the equipment from the closed line was able to be used in the new prototype plant. Despite the smaller scale of the project, it successfully designed, tested and then demonstrated the new manufacturing process for artificial stone without the use of chemical compounds. The main change was the substitution of polyester resins by pasty mixes, which enabled the avoidance of two of the most environmentally damaging steps: sintering and assembly. The use of a mix of hydraulic bonding agents and limited water, and also eco-friendly pigments meant that VOC emissions were avoided. The material for the stone could be poured into silicone moulds without any excess, reducing waste material from 0.6kg per piece to zero. Furthermore, any pieces failing to meet quality standards were re-used in the process, reducing the amount of waste material from 19.8 kg/m2 to 0.1 kg/m2. Since no water is needed for rectification operations, 4.5 l/m2 of consumption were avoided. Casting by pressurisation meant that hardening could be done at room temperature without the need for the drying chamber, saving over 2.5 kW h/m2 of gas consumption. It also provides a more homogenous final product with enhanced mechanical properties and an appearance of natural stone. From the environmental and health and safety point of view, the new process, which avoids the use of volatile solvents and other toxic products, will significantly improve the working conditions in the factory and reduce air emissions coming from the manufacturing process. The final product meets sustainable construction life-cycle parameters and can thus hope to open a new market niche for the eco-products line in the construction sector. Further benefits of the cleaner, simpler process include 15% lower production costs and improved working conditions. For the beneficiary, its production can be a way out of the current economic crisis in line with the Lisbon strategy goals. Further information on the project can be found in the project's layman report and After-LIFE Communication Plan (see "Read more" section).