The rare Recipe for this bright blue building-block with small tiles can occasionally be found in Stone Treasure Chests on the Fossil layer underground, in Obsidian Treasure Chests on the Stalactite Layer, in Iron Treasure Chests on the Lava layer, or in Diamond Treasure Chests on the Corruption layer. After finding the recipe and learning it (by dragging it over your character's/toon's portrait), you can then craft Blue Adobe Floor building blocks in your Crafting Menu (default key "Q") - or at Crafting Tables (that still exist in worlds created before R22 on September 16th 2015).