The type of adhesive you should use depends on the end product you want. You can use PVA, weldbond, cement adhesive, or silicone to create your mosaic masterpiece.  Cement adhesive is best for outdoor pieces, PVA is great for indoor projects, silicone is best for glass, and weldbond is the most widely used glue among mosaic artists.  Do not use Elmer’s school glue because it is not strong enough. Avoid hot glue because it dries instantaneously and is not optimal for a lasting mosaic.