These glass block from the Design series, called Pegasus has long flanges than the standard 'basic' glass block. This can be made smaller joints in bricklaying these stones. These stones are thus often used for showers and interior walls. The joint thicknesses can 2mm! be made. This gives you more glass and add less visible. Grouting can be done with a standard waterproof joint, just like normal tiling. These stones are specially ordered and can not be sent back.