How to Easily Build Tile Molds!

So I get this wild hair about making tiles for my pot (no, not the stuff you smoke ... containers) garden. I wanted to replace the brown plastic tiles that are now five years old and showing some age, and are no longer worthy of the pot garden. I poked around Lowes and found some nice 16" tiles for fiveish dollars each. Bringing my total to around $100 to make a new lounger deck. But no...I see on Pinterest this beautiful set of stairs that had been tiled with an eclectic assortment of hand painted tiles (damn you Pinterest). I din't pin it and now I can't find it again but still I found the following on Pinterest and decide I just have to have something like it. So begins the journey.

Love this!!!

I started by calculating the size I would need based on the anticipated shrinkage of the tiles in the

making. I drew  several designs until I found one that spoke to me and then I made a couple of variations to go along. In total I decided on four different but connected tile designs. I cut squares of plastic (a cutting board) that are the correct depth and modeled clay into the design on each. Then I made plaster molds of each.

Finished tile waiting to be cast.

I have made plaster casts before but always randomly so I just used some foam core for the box. This time I made this so I would be able to cast several items of varying sizes moving forward.

Plaster setting up for pouring.

Plaster has been poured. I lightly shook the mold for
several minutes in order to get the air bubbles out. 

 A little leakage of plaster. I added more clay around the sides to the next casts I poured. 

Finished mold. Still had a a few air bubbles so I shook the next ones even longer.

Original after casting.