A project comes off the list -- sort of

Every gardener has a list of projects that they'd like to do each year, don't they? I know I do. In fact, my list of "things to do this summer" seems to stay quite similar every year, as I never get around to all of the items. One task that's been on that list for a few summers is "make more hypertufa pots". Hypertufa is a lightweight concrete that is easy to work with and great for lots of different garden projects.

A couple of years ago I made these small balls out of hypertufa, and they add a nice sculptural element to one of my planting beds. But I want to make something more useful, and what's more useful than pots? I never have enough sturdy pots.

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Oh, I just remembered I've made some other decorative pieces before too, but again, they aren't very useful:

These were going to be a small water feature.

So what exactly is hypertufa and how do you make it? It's quite simple: hypertufa is an artificial rock. If you're familiar at all with concrete, you know that it's very hard, but very heavy. That's because concrete is made when portland cement is mixed with sand and small rocks. Hypertufa is also made with portland cement but uses lightweight materials in place of the sand and rock. Typically peat moss and perlite are used, and although there are many different recipes that's what I'm going to use.

You probably already have peat moss and perlite, right?

You can find portland cement at any home improvement center. You don't want ready-mix or anything except straight portland cement:

It's no trouble finding portland cement, but it might be getting it home, as it typically is only available in 94 pound bags (here in the US). Remember, lift with the knees, not with the back!

I'm going to use an easy-to-remember recipe that uses equal parts of all three ingredients. I'll start with the peat moss, and I'm going to filter it through some hardware cloth:

This will remove all of the little sticks and break up any large clumps:

You'll have better results and fewer weak spots in the finished product if you do this.

Perlite goes in next:

I have a craving for cottage cheese now for some reason.

That's a lot of dust, so wear a mask and don't do this inside the house! The cement dust is particularly bad to breathe, so please don't!

I'm mixing in a clean garbage can because my wheelbarrow is full right now. It's a good idea to mix together the dry ingredients before adding any water -- it's much easier to do that way.

I've mixed cement, mortar, and grout before -- they're all quite similar -- and I never know exactly how much water to add. What I do know is that adding too much water is very bad, so add much less than you think you'll need and go from there.

I was using a large yogurt container to measure the ingredients, and I used 2 full containers each of perlite, peat and cement. I started with 1/2 container of water, mixed a little, added another 1/2 container, mixed some more, then tested to see if the mix would stick together:

Yes it would, but it's still a little too dry, so I added more water, little by little. I lost track of how much water I ended up adding, but I think it's probably better not to know how much water you should add, and just go by how the mix looks. That will keep you from dumping all of the water in at once, which is the best way to end up with a mix that is too wet.

I pushed the mix up against the sides of the bin with the shovel to test it, and it looks pretty good now.

Since I'm going to make a pot, I need a container to use as a mold. Luckily I have plenty of buckets and other plastic planters, so I chose a big planter that has a rounded bottom and tapered sides:

Tapered sides will make it easy for the pot to come out of the mold. The lack of little edges and holes helps too. A liberal amount of cooking spray oil or mold release spray will help also -- I don't suggest skipping this step. I suppose you could rub regular cooking oil into the mold too if you don't have spray oil, but a dry mold -- unless it's cardboard or something that can be dismantled -- might make it impossible to get the pot out.

Then it was just a matter of taking handfuls of the mix and pressing it onto the bottom and sides of the mold and packing it together. I didn't take any photos of this process, since my hands were covered with "mud" and it's hard to find a cement-proof camera these days. Here's the finished product though:

I'm not certain that the top edge was level all the way around, but hypertufa pots are somewhat rustic by nature, and some unevenness wouldn't be out of place. Plus I knew I could shape the edge after the concrete set but before it was completely cured (hardened).

So all that's left is to wait. I covered it with plastic to help retain the moisture and set it aside for three days. I kept it in the garage, where the temperature was about 50ºF (10ºC). You don't really want it to freeze, and you don't want it too hot as you want the water to react with the cement, not evaporate.

After the third day I worked to get it out of the mold. It didn't pop right out, but I tapped on it for a few minutes, eventually banging it on the ground a little bit. Since the planter was double-walled (hollow inside) it wasn't easy to flex, but just as I was getting frustrated the pot suddenly released and fell into my hand. Good thing I was paying attention.

That edge is definitely a little rough, but I can fix that with an old file, a wire brush, or even a scouring pad (a soapless one) -- something that will wear the hypertufa down, smoothing it a little. So I did that...

It might need a little more smoothing, but this is pretty good for today. I'm pretty pleased with the texture of the outside surface, and I like the overall shape too.

The inside is quite rough, but who cares about the inside! As long as there are no cracks and it's sturdy, it's fine. (If there were cracks I'm not sure what I could do about it.)

I'll drill some drainage holes with a masonry bit at some point, and I will let this cure for several more weeks before using it -- I think I read 3 weeks is an appropriate curing time. I can spray it with water every day or so to assist in the curing process, but this is optional. It will be weaker if it dries out too fast though.

So that's my first hypertufa pot of the year, and it's not even March yet! I'm quite pleased with this one, so I'm certain I'll be making more in the near future -- so I'm leaving it on "the list". Actually, I'm quite excited about making more now! I've got a few mold containers in mind already...
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