I just completed my first hypertufa project and it was a big one. A 32x6 inch millstone I'm turning into a fountain. It was both harder and easier than I expected. I wanted a larger piece than the concrete one I just finished. It was 32x3.5 inches and weighs about 250 pounds best I can figure. The hypertufa millstone is still curing, but I estimate it will probably weigh about 250 pounds also.

I made the mold out of a piece of plywood for a base and used a 25' piece of 6" flashing for the circular mold. The center hole was a piece of PVC pipe wrapped with wax paper.

The formula I used was 2 ninety pound bags of Portland cement (2cf), 2cf of medium vermiculite, and 2cf of strained peat moss. For reinforcement I mixed in a good bit of polyester fibers, for color I added dry brown tint, and for additional strength I added a gallon of acrylic fortifier to the water.

I rented a small cement mixer and thoroughly mixed all dry ingredient before adding the water. The hard part was getting it mixed right. When I started adding the water it really started to ball up but I had read someplace that just means you needed to add more water. We played around with it for quit a bit before I decided we had to start putting it in the mold even though it really wasn't runny at all. ( Note: after the fact it was clear I just needed to add a bit more water and it would have been a lot easier. ) We dumped the mix in the mold and I pounded it tight with an old brick and then used a cement trowel to smooth the surface. Let it sit for about 15 minutes and then put some grooves in the top for realism. On the second day I pulled out the PVC pipe in the center. On the third day I took the mold off and it was perfect as you can see in the pic. I kept it covered for three days After four days it already felt hard as a rock. I waited a week and then mounted the fountain on it's base. She came out really nice. I'm playing around with the idea to stain it a little darker, don't know yet.