You have probably seen those big planters and troughs in pictures of old English gardens. They are most likely made of Tufa rock.
It is fun to play with. You can shape it, file it, form it, add to it the next day as long as you do not let it dry out. (just cover with a piece of plastic) It can withstand the coldest winters and loves the rain. The longer you have it the more character it gains.
If you want to make something big, this is the stuff to use.
It is not waterproof so no ponds. You can try to seal it but would be better off to use concrete. It would be cheaper and far less aggravation.
You can use it for fountains that do not have to hold water. What I mean is that the water will not be sitting in, just passing through.
It is relatively light compared to concrete so makes great trough style planters. If you have ever wanted to make a “Giant Head” statue it is great for this because you can take your time molding and add to it as you see your statue taking shape. If you do not like what you see, it is easy to knock off a bit and change it. When you are done it will, unless it is 3 or 4 feet high, be possible to move it without a forklift or crane.
Like the natural Tufa, it supports the growth of Moss and Lichen. This gives it an aged look in one growing season.
Once you get started with this you will be hooked. It is great for use in molds, you mix as usual and press it into the mold. In a couple of days, when it is cured, you can take it out and you will have a light, textured looking casting. These are nice when lightly stained, or given the moss growth formula.
Mix up a batch and try it!