Wedi building boards have a blue core made from CFC-free extruded polystyrene rigid foam. This makes the wedi building board an ideal basis for any type of plaster and tile. wedi building boards can be applied to practically any substrate, are waterproof, insulating, versatile, light and robust. Wedi building boards are perfect for wall and floors and give the perfect surface for tiling. Wedi building boards conform to building regulations and are perfect for waterproofing and tanking a bathroom or shower prior to tiling.