Things You'll Need
2, 1-gallon plastic containers
Vegetable cooking spray
Large plastic bin
Hose or water pitcher
Plastic garbage bag or plastic sheet
Sand is a key ingredient in a classic formula for hypertufa, the material often used for casting garden planters or even faux boulders. Once hypertufa has dried, the piece you've made looks as if it were carved from stone. One basic recipe calls for equal parts sand, cement and peat moss, which results in a pot resembling limestone. As you become proficient, you can vary the proportions to create different colors and textures and even substitute perlite or vermiculite for sand. Many hypertufa creations use course sand found at home building stores.
Turn the pots you will be using for molds over. Scrape and wipe off any dirt or debris from the exteriors.
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Spray the exteriors of the overturned pots with vegetable spray, making sure to evenly cover the sides and the bottom of the pots.
Set the pots onto a plastic bag or drop cloth.
Put 1 part sand, 1 part cement and 1 part peat moss in a plastic bin. Proportion is more important than amounts, but if you figure on about 8 cups of each material, you'll have enough hypertufa for two 1-gallon pots.
Blend the ingredients with your gloved hands until they are evenly mixed and any lumps are broken up.
Pour water in very slowly until the hypertufa is the texture of cottage cheese. Test for sufficient moisture: Squeeze a handful. It should retain its shape; if it doesn't, gradually add more water. If it is too wet, gradually mix in equal parts of the sand, cement and peat moss, until you have the right consistency.
Making the Planter
Use your hands to scoop the wet hypertufa material over the overturned pots. Aim to achieve the same thickness on all sides and on what will be the bottoms of each planter.
Press down on the bottoms of each pot so that they will have a flat surface when turned right-side up.
Poke, using your finger, at least one drainage hole in the bottom of each planter. Remove the wet hypertufa from these drainage holes.
Cover the planters with a plastic bag, and leave to harden for 24 hours.
Remove plastic sheeting and turn the planters right-side up.
Remove the pot molds from the interior of each hypertufa planter.
Make any finishing touches you desire. Pressing pebbles into the surface is one way to decorate. Roughening the surface with a dry brush creates a different look.
Leave the planters, again in plastic wrap, to cure for 48 hours.
Unwrap the planters, and leave them outside for an additional two weeks, hosing them off at least once a day to rinse away lime from the cement. If not rinsed off, the lime can leach into and add too much alkaline to the soil.
Set the planters inside a vinegar-water solution for 30 minutes to further neutralize any lime. For every 1 gallon of water needed, add 1/4 cup vinegar. After removing the planters, let them dry before filling with potting soil and seedlings.
If using course or grit sand, remove chunks with a garden sieve that has about one-quarter mesh.
For large containers, use 1 part each sand, perlite, Portland cement and peat moss. Alternatively, add about 1/2 cup of fibermesh pellets to the basic recipe for extra stability. Fibermesh is sold in stores that carry concrete and related supplies.
Molding a planter over an overturned mold is one of two basic ways for creating a hypertufa container. The other involves placing the wet hypertufa material on the interior of the mold, sometimes placing a smaller mold inside so that the hypertufa is sandwiched between two containers as it cures. This can make for a more symmetrical presentation, but removing the hypertufa planter can be challenging unless you've taken special care to thickly coat the both molds with spray.
If you are working in a different area than where the planters will be curing, build them on a board covered in plastic, and move the board to a shaded area to cure.
Wear gloves and a face mask when mixing the dry materials and molding the hypertufa over the mold, as they can irritate skin and lungs.
Follow exact recipes. While hypertufa can be made with either sand, perlite or vermiculite, for example, don't substitute one for another. Formulas have been worked out using the proportions that work best for each material.