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I saw a home recently that had a stunning master bathroom. Natural slate floors and shower (all were 4" squares)...really nice looking.
One of the things that made it so unusual and interesting, IMO, was the seamlessness of it...in other words, the squares butted tight up to their neighbors, with no grout visible.
At the time it did not occur to me to look more closely, but... how is this done in a wet environment?