Protective Clothing: While working with hypertufa ingredients, wear a dust mask, sturdy rubber gloves and protective eye goggles when measuring and mixing the dry ingredients. Once you've added the water to your mix and have it mixed up a bit you can remove the goggles and dust mask. Cement and perlite dust is toxic and you don't want to breathe it in. Work in a well ventilated area and wear old clothes (if you're messy, like me).
Recipe: The mix I use for my hypertufa is one part Portland cement, 1½ parts sifted peat moss and 1½ parts perlite. This is the recipe I use most for pots. I don't measure the water, just pour and mix it in slowly until when I squeeze a handful it just sticks together, not wet or soggy. You don't want to add too much water because that weakens your finished product. Another recipe which will make it a bit stronger is 1 part each Portland cement, play sand, sifted peat moss and perlite. The sand will make it a little heavier, but stronger.
Instructions: You can use just about anything you want for a mold. Just be sure it has smooth sides because if there are ridges in your mold you won't be able to slide your pot out. Also make sure the top of your container is not narrower than the bottom or the pot won't come out.
I like to make my pots inside the containers I use for molds but you can also turn something upside down and make your pot over the outside of the container. For me it's easier to be able to see how thick the sides of my pot are if I use the inside. Some people also use one container inside of another and pack the tufa between the two containers. That's not as easy as it sounds.
You'll need to prepare your mold prior to use. Hypertufa will stick to unprepared surfaces and you won't be able to unmold your pot. I generally use stiff plastic things for molds. You want something stiff so the sides don't flex during contruction or your pot will crack. I spray the inside of my mold with Pam cooking spray, then line it with a plastic bag. Dry cleaner bags work great as do grocery bags, garbage bags, etc. If there is printing on the bag place it facing the mold, not your hypertufa mix.
As you're building your pot the sides and bottom should be at least 1" thick for strength. The bigger the pot, the thicker it needs to be. Pack your tufa in the mold as firmly as you can, I mean really push down hard. If not, it will just crumble when you unmold it. If you use a mold with corners make the pot thicker in the corners for strength.Remember to put a drainage hole in the bottom. I do that by sticking a wooden dowel or piece of PVC pipe through the bottom as I'm building it. You can pull it out when you unmold it. Clean all your tools immediately or the cement will harden on them. Never, ever pour "used" water from this down a drain or you'll cement the drain shut!
Your pot has to remain in your mold for 24-48 house before you try to remove it. The larger the pot, the longer it needs to sit. After you're finished putting your tufa in the mold, put the entire thing in a large garbage bag and seal it tightly for 24-48 hours. Try to move it as little as possible during this time to prevent cracking.
To unmold, gently turn the mold over and your pot should slide out. One reason for the plastic bag in the mold is so that if it sticks you can gently tug on the plastic to get air in between the pot and the mold to release it. Tufa is extremely fragile at this point! If you bump or drop it, it will shatter.
You may notice that there are lines in your pot from the plastic bag. Now is when you can remove those and/or roughen up your pot to make it look more rugged. I use a wire brush for that. You can also use a large file to soften the edges or corners. Be gentle or you can accidentally take a chunk out of your pot! And wear your protective gear during this process too. Now it's time for the rest of the cure.
Curing: Because of the temperatures here in Wisconsin, it's not safe for me to start making tufa/cement projects until the end of May or early June. Curing needs to be done at a minium of 50° F. When you cure tufa you can do it a couple of ways. After you unmold it, it needs to remain moist or wet to cure properly. You can stick it in a sealed plastic bag (garbage bags work great) out of direct sunlight and then mist it every day; or just stick the piece in water. I use big Rubbermaid containers (or something similar), then I don't have to spend the time misting it. I change the water every couple of days because it gets yucky (real technical term).
There are lots of opinions about how long to cure the pots before planting in them - anywhere from a few days to 28 days. I personally cure them for 28 days in a waterbath. It "officially" takes concrete 28 days to cure well (but I guess it actually keeps curing just about forever) and I prefer being on the safe side. I know a lot of people only cure for a few days and seem to have good results, so I guess it's up to you. It's hard to wait 28 days - especially when you first get started!
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