Hi Juimjun. Have a look at either Bampy´s blogs or mine. The blogs are about Hypertufa pots and troughs...they might interest you..they also say about the mixture that is used.

Its 3 sand to 1 cement jimjun ok . mix the sand and cement together thouraly and dont use washing up liquid . you can buy plasticiser from b and q for a fiver or so . anything else ypu want to know just ask .