How do you make planters with vermiculite and cement?

I haven't seen vermiculite used this way (most likely because it has fallen out of favor due to causing asbestosis like lung damage) but there are a lot of recipes for Hypertufa. Hypertufa is a mix of Portland cement, peat moss and pearlite. It is generally 2 parts PORTLAND cement, 3 parts sifted peat moss, and 3 parts pearlite (but I've also seen recipes for 3-4-5 parts respectively). Mix together with water to make it the consistency of a mud pie. You'll want to have prepared a mold of some sort (nesting cardboard boxes of the same shape but different sizes work well, but you can also use a mound of soil or sand covered in plastic sheeting, a styrofoam cooler, foam insulation sheets, etc). Molds made of wood will have to be lined with plastic or the Hypertufa will stick to it. Put an inch or two of the cement mixture on the bottom of the larger box. At this point you can insert plastic covered dowels or something like that to produce drain holes but be sure they aren't taller than the layer of cement mixture. If you don't insert dowels now you'll need a masonary bit and a drill to make drain holes after it dries. Put the smaller box inside resting on the cement mixture then begin packing the cement mixture into the sides. Pack it in pretty well. Let this sit for 24 hours in a shady place before removing the boxes (longer if it is thicker than 1 1/2 inches). You can use a wire brush to "age" it at this point. The planter should continue to cure for about 3 months before using it. Failing to allow it to cure will result in damage to the planter. Cure it out of direct sunlight and if possible under plastic to deter cracking caused by uneven curing. After curing you might want to treat the inside of the planter with a vinigar/water solution to neutralize the acid from the lime in the cement (some people say it isn't necessary, but if you have invested money in the plants that are going in it then I say it's worth the extra step) Hope this helps!