Trencadís is a type of mosaic used in Catalan modernism, created from broken tile shards. The technique is also called pique assiette. This mosaic is done using broken pieces of ceramic, like tiles and dinnerware .
The Catalan architects Antoni Gaudí and Josep Maria Jujol used trencadís in many projects, among which Barcelona's Parc Güell is probably the most famous.
Modernist architects made extensive use of ceramics, but Antoni Gaudí in particular proposed a more unconventional method. He covered his three-dimensional architecture with glazed ceramics of different shapes and colours, which created brightly coloured patterns. For the task, he used discarded pieces of ceramic tiles collected from the factory "Pujol i Bausis" located in Esplugues de Llobregat, and pieces of white ceramic from broken cups and plates discarded by other Spanish manufacturers.
The technique was used for the first time at the Güell Pavilions where the complex architecture forced him to break the tiles where he couldn’t use an entire square one.[source]