Casting in hypertufa is fun and not at all difficult. Hypertufa is a mixture of Portland cement, sand and peat moss. If you want you can replace the sand with perlite, it makes the pots and trays a lot lighter as perlite weighs almost nothing. Tufan takes a little longer to harden than ordinary concrete.
When casting bigger things it is a good idea to reinforce the castings. In my first attempt, I used chicken wire but I found it difficult to fill the hypertufan in the mold when the chicken wire was there. Then I bought a woven glass fiber cloth, which I unraveled. I cut the fibres into 3-5 cm pieces. One handful of this mixed in each batch hypertufa seems just right. This reinforce and holds the Tufa together without problems.
A concrete mixer is very useful and makes the casting so much easier. I bought the smallest one I could find and It is just the right size for my needs.
When casting larger pots and trays, I use buckets of different sizes ordinary cardboard boxes and plastic tubs as molds.