Hypertufa is similar to concrete, but instead of traditional aggregates, peat moss and perlite are added to portland cement. With their simple shapes, these mushrooms are a great first hypertufa project. Before you dive in, please look at my two "Hypertufa 101" articles. Click here for the first article and here for the second. Reading them will give you a good idea of how to work with this material, step by step from material list to finished project.
The basic mushroom shape has two parts, a stem and a cap. Turn a plastic bowl upside down, and you'll see a great shape for a mushroom cap. Similarly, a plastic tumbler, sour cream container, etc. makes a good stem. Flexible plastic molds are easiest to work with. Metal or glass would work in a pinch, but this isn't a time to break out the good china. Avoid ridges and inward curves that will keep the hardened concrete from sliding easily from the mold.
The trick is to match the size of the stem to that of the cap. Turn the plastic cup upside down, and put the upside down bowl over it, remembering that the bowl will actually be raised an inch or so above the top of the stem. Cereal bowls paired with yogurt containers, mixing bowls and tall plastic glasses, punch bowls and nursery pots - you can make terrific mushrooms in many different sizes!
Get your work surface ready. Sturdy cardboard or plywood is useful under your pieces. You'll also want plastic bags to pull up and around the stems and caps while they're curing. Mix your dry ingredients in the following ratio: 2 parts Portland cement, 3 parts peat moss, 3 parts perlite. Cement is caustic, so wear a mask and gloves while you work. Add water to the hypertufa a little at a time, until your mix holds together well. When you squeeze a handful, it shouldn't dribble water, but it shouldn't crumble either.
Prepare your container molds with a generous coating of cooking spray. Add extra inerest to a mushroom cap by lining the container with a crinkled plastic or paper bag before spraying. Make a few "straight up" first, though, especially if you're new to working with hypertufa. Same goes for adding colorants, substituting ingredients, or changing the suggested ratios; get a feel for the basic method before you start experimenting. If you stray too far from the "recipe" or skimp on setting and curing time, you'll end up with a sad handful of gravel.
Hypertufa is pretty forgiving, though, and these mushrooms are simple and quick to make, so don't over-think this project either. Gather the molds, mix the hypertufa, and just get going
Fill the stem first, since you'll use it again while molding the cap. Pack the hypertufa firmly into the mold, pressing hard so the supporting stem will be dense and strong. Level off the ‘tufa at the rim of the container, if your mushroom needs to stand upright on a floor or patio. If you'll be putting it in a garden, consider pushing a metal rod into the stem, so the mushroom can be staked in place.
Now make the mushroom cap. Start by pressing some ‘tufa into your mold, covering the bottom of the bowl by an inch or two but not getting as high as the rim. Put the filled stem mold down onto this bottom layer, centering it in the cap. Continue to pack the moist hypertufa mix into the bowl, working around all sides of the stem until the bowl is full. Bumps and uneven surfaces are fine; they'll give your mushroom an "organic" look.
Leaving the stem and cap together as the hypertufa hardens helps ensure that the two pieces will fit together in the end. Seal them in a plastic bag and let the hypertufa set up 24 to 48 hours. With larger projects, it pays to plan ahead and put an open plastic bag on your work surface, so you can draw the edges up and over your mushroom.
After the hypertufa has set, you shouldn't be able to dent it with a fingertip, although you'll still be able to scratch its surface with a fork (or with your fingernail, if yours are sturdy). Take your time unmolding your pieces. You should be able to separate the cap from the stem with a twist and perhaps a little wiggling. I had one mushroom that was joined so stubbornly that I finally gave up and cut the plastic cup off with a knife.
To get caps and stems out of their molds, start with gentle squeezing all the way around, like loosening a rootbound plant from its pot. I also like a technique I learned for un-molding bundt cakes. Put the piece upside down on a board and hold it firmly in place while giving it a few brisk shakes from side to side. A small but firm downward motion should shake it out. Remember, you can always try again to release a piece from its mold, but if you crack it by getting too vigorous, there's really no fixing it. Fortunately, these mushroom parts are easy to make in multiples, giving you some back-ups (or extras if you get lucky).
Freshly unmolded ‘tufa can be wire-brushed or carved with a decking nail to add texture. Now your mushroom pieces need additional time to cure while staying moist, either in a plastic bag or in a water bath. 30 days isn't too long, if you want a strong piece. Fall is a great time for hypertufa projects, since they can stay outside and continue to cure in winter snow and rain. When cured, match up your mushroom caps and tops, and you've got some great garden accents!
Making hypertufa mushrooms by yourself is fun; making them with friends (or a favorite niece) is even better. I'm looking forward to a hypertufa mushroom workshop with my mid-Atlantic gardening friends.
Photos by Jill M Nicolaus. "Mouse over" images and links for more information (put your cursor on the photo and hover there for a few seconds; a pop-up caption should appear).