I found this information at the-artistic-garden.com:
Hypertufa (pronounced hyper-toofa) is the term used for a type of artificial stone. It was first created in the mid 19th century by mixing sand, peat, various volcanic aggregates and cement. It’s relatively lightweight compared to stone or concrete and no matter how cold your winter temps may be, if properly cured, is freeze proof.
Hypertufa was concocted to be used as a substitute for the natural volcanic rock called Tufa. Tufa has been used for making Alpine style planting troughs. Unfortunately, it is not readily available anymore.
Most deposits have been depleted and it is increasingly difficult to find. I've read that there are only two deposits left in the United Kingdom, with a site in Wales having the best quality; there is some in East Germany; there are a few deposits left in the United States; and Canada has an excellent deposit located in Brisco, BC.
There are different recipes you can mix up. It depends on what end result you’re desiring -- lighter in weight? More durable? Want to carve it? Basic hypertufa recipe ingredients are varying combinations of Portland cement, peat moss, sand, perlite, or vermiculite, and water.
Another big part of the whole process is patience. Many hypertufa projects can be ruined by not allowing enough time for the mold to set and cure, and end up destroying their work because it wasn’t ready to be unmolded yet.
OK, now we know what hypertufa is. It's a mud-pie recipe that, given enough time to cure, can create rock-like creations, often in the form of planters.
In our case, DH wanted to make simple hose guides out of the stuff.
Starting with a 12" galvanized spike, the plan was to mold the mudpie mix around the head in the shape of a thumbtack, let it sit, then pound the spike into the ground in the garden.
So, I'm looking online for recipes, ideas, a general instruction manual. I'm seeing all different types of creative uses for the stuff.
"Hon, can you make it in the shape of a bunny?"
"A bunny. It'll be cute. We need a bunny in the garden.""It's a hose guide. It needs to be in the shape of a thumb tack... to guide... the... hose. Not a bunny."
Quick thinking, I grab a sheet of scrap paper and a pen and scribble out my idea of what a thumbtack looks like.
"Viola, thumbtack, right?"
"Ok, now, ... scribble scribble scribble.....thumbtack-bunny!"
I think I broke his brain.
Needless to day, this thing here did not happen. This did:
So here's the deal: you can mold it, but as mentioned previously, you have to let it cure. These guys are sitting outside in our breezeway covered with plastic grocery bags.
Below is what they look like uncovered and uncured. This is after about 24 hours.
It looks kinda wonky, but after a few days, it should harden enough to place upside down in the garden... spike side down, and hopefully keep me from trampling my dahlias with the hose.
btw: the longer it takes to cure (slower is better, so avoid hot days) the stronger it will eventually be. You can keep them covered and let them cure anywhere from 2 days to a week.
Oh, and I got my bunny.
Recipe to follow: (Hon, this is where you tell all the great folks what sloppy mess you made in the breezeway with the peat moss. hint hint.)
For hose guides, I think a harder mixture is fine. They aren't that prone to cracking and they don't need to be THAT rustic. I used a 1:1:1 mixture, which is 1 part portland cement (NOT concrete mix), 1 part sand, and 1 part peat moss. Don't add too much water as the peat really soaks it up and then the mix becomes much wetter than your realize when you start forming it. If the mix is too crumbly, add just a bit more portland.
After curing for a couple days, I'll take a wire brush and round off any rough edges and make the hose guides look like stones. Then I'll cover them up again for a while, or until Mrs. OrDie decides that she must have the guides in the garden. If I can get another couple weeks, it would be great. These things are very alkaline so, be advised that they can alter soil nearby for a while. In time, though, they'll be fine and will start to get moss on them. They quickly become very unobtrusive.