To increase structural strength for weight bearing loads. Add synthetic reinforcing fibers or cloths (plastics, not fiberglass). Liquid acrylic resins may also be incorporated into the mixture for elasticity and longevity. Stepping stones, retaining wall rock, and benches are some of the examples of projects that will need this kind of reinforcing. This garden rock wall in the Netherlands was handcrafted of hypertufa. Some of them are 2 m high!
Curing takes moisture, time and temperature. When you are finished crafting your piece wrap it in black plastic, or put it in a large black plastic bag. Mist with water and seal tightly. If you can get your piece into direct sunlight, that’s the ideal place. If not, find the warmest spot. If you use a heat lamp, keep it far enough away from the plastic so that there is no danger of melting plastic or overheating the hypertufa.
The temperature and moisture ‘steam’ the hypertufa and make a strong product. After 24 hours check to see if the hypertufa is dry enough to come out of the mold. The way to tell is to scratch the surface with your fingernail, if some comes off, mist it, and wrap it up for another 12 hours.
When you can’t scrape hypertufa any off, then take your piece out of the mold, mist it and recover it for a few days. Curing can take up to 28 days.
You can use it as early as 7 days after the mold is removed, but what you get in speed now costs you in longevity later. Hypertufa is a great project for winter when you can’t get out to do other gardening. Then you can afford to be patient.