Pour mortar powder into an old bowl and slowly stir in water until the mix looks thick yet smooth without lumps or being runny.
Spray cooking spray along the inside of the mold you want to use. Plan to make three or four feet for every plant you want to prop up.
Scoop mortar mixture into the molds to fill soap or planter feet molds to the top and egg carton or cup molds to 1 inch deep. Set the filled molds aside to dry for 24 hours.
Spread out an old towel on a flat surface. Turn the molds upside down and hold them above the towel. Press downward on the molds to pop the pot risers out of the mold onto the towel.
Set the risers out for one to two days to cure and harden.