Skeewbackers are super lightweight, waterproof mosaic backers. they are rigid and at the same time shapeable. use them indoors and outdoors in wet or dry environments. they are made from Wedi board - a polystyrene foam sandwiched between two thin layers of reinforced concrete and come in 1/4" or 1/5" thickness.
Have you tried Wedi Backers? They are wedi board in perfect sizes for your mosaic art.
The ideal lightweight, all weather mosaic substrate. Wedi board has an engineered foam center and a thin layer of cement and fiberglass mesh on each side. Great for interior and exterior projects. Wedi board can easily be cut with a utility blade or cut into shapes with wood power tools.