The tiles are just cardboard and the red are magazine pages I kept ages ago as I liked the color.
Then someone on Twitter suggested that Chakotay also helps with the tiling. I think that is an excellent idea and Kathryn thinks so too ;) Here he is doing the ground tiles.
I found a method how to lay the tiles very quickly. I put up a ruler and so I could push them against it and would have a clean line.
And here is a post with the finished bathroom: https://dieastra.livejournal.com/354677.html