Choosing a Mold
Pick something that is light and reusable, such as old metal or rubber dishpans, kitty-litter trays, old plastic pots or saucers, or anything that has a desirable size and interesting shape. Or for larger containers, you can even use rubber cement-mixing containers or livestock feeding and watering troughs that you might find at a hardware or feed-and-seed store.
Tool and Equipment
- Thick rubber gloves with extra-long sleeves
- Container or bucket to measure ingredients
- Large, shallow container or wheel barrow for mixing the ingredients together
- Watering can
- Plastic garbage bags or plastic liner
- Short dowels with at least ½ inch diameter
- Wire brush
- Old paint brush
- Optional: fibermesh, or ¼ inch hardware cloth, wire, and tinsnips for reinforcement basket
- Optional: decorative stones
- Cement: Use Portland cement rather than pre-mix cement to eliminate the gravel that comes in the premix cement. This will result in a more natural texture in the finished container.
- Sand: Use Mason’s sand rather that coarser grades of sand because it bonds stronger to the cement. You can also substitute perlite for the sand because it is much lighter. However, this will give a bumpier texture to the finished container.
- Peat Moss: Use milled peat moss and sift out any unmilled chunks or sticks of wood.
- Concrete Colorants: These are powders that can be purchased at building supply stores and come in various shades of brown, black, yellow, and green. You can use just a pinch of colorant (per batch of mixture) or a combination of a couple colors to warm up the cold gray color of the cement.
The proportions of cement, sand, and peat moss affect the texture of the finished hypertufa container. You can experiment with different proportions of ingredients to find your preferred texture. Always measure the materials by volume rather than weight.
For instance, for a porous texture like tufa:
- 1 part Portland cement
- 1 part mason’s sand or perlite
- 2 parts milled peat moss
Or, for a denser texture like sandstone:
- 1 part cement
- 1 ½ parts mason’s sand or perlite
- 1 ½ parts milled peat moss
Mixing and Molding
- Cover the molds with thin sheets of plastic, such as garbage bags, wherever they might come in contact with the hypertufa mixture. This will keep the mixture from sticking to the mold as it dries.
- Mix the milled peat moss and sand (or perlite) together. Then, add the cement and mix well. Add any colorants you desire at this point and mix well again.
- Once all the dry ingredients are mixed together, you can start adding water, a little at a time, stirring the mixture thoroughly after each addition. The mixture needs to be fairly dry, just wet enough to bind the materials together.
- Fill the bottom of the mold up to 1 ½ inches deep. Firmly, press the mixture down to eliminate any air pockets. Using the dowel, carve out several drainage holes. Then, continue adding the mixture to build up the sides of the mold. Firmly pack the hypertufa to make the walls approximately 2 inches thick.
- Let the container sit and dry 21-48 hours (or longer if the mixture was more moist) until it is dry enough to handle but not too dry to “weatherize.”
- Weatherizing gives the hypertufa the texture and character of an old, worn stone. Remove the semihard container from the mold and take off any plastic that might have stuck to it. Take a blunt object, like a chisel or stick, and gouge and bash the container. Then, take a wire brush and scour it. Finally, brush off any dust or debris with an old paintbrush. Set the container in a place where it can cure undisturbed for 4 to 6 weeks. Do not set the container in the sun or in freezing temperature until it has fully cured.
- After it is fully cured, you need to neutralize the chemical before it can be planted. You can do this by placing the empty container outside for several weeks where it can be washed by the rain. Or you can speed up the process by using potassium of permanganate crystals (available at industrial-chemical supply stores) mixed with water to make a solution that can be brushed over the surface of the container and allow to sit for several hours before being hosed off. Dispose of the used solution away from plants and animals.
- Not it is ready to be planted.
Extra Tips & Ideas
When making large trough-size hypertufa container, you may need to use reinforcement for extra structural strength. You can use hardware cloth to make a “basket” slightly smaller than the mold. Fill the bottom of the mold with the hypertufa mixture about 1 inch deep. Then place the hardware cloth basket in the mold. Add more of the mixture and press firmly to form the bottom and sides of the container at least 2 inches thick. Or you can use a polypropylene product called fibermesh, which you mix directly into the dry mixture. Use a mixture of equal parts cement, peat moss, and perlite, then add ¼ cup of fiber mesh per gallon of mix and stir thoroughly. Add water as in step 3 and continue to make the container following the directions in steps 4 through 7.
If you desire to make stepping stones, you can use plastic pot saucers of a desired size (lined with a plastic garbage bag so the mixture won’t stick) or you can make a reusable mold out of a 2 inch wide fiberglass strip about 52 inches long and formed into a circle. Overlap the end of the fiberglass about 4 inches and secure with wing-nut screws that can be tightened when the mold is filled by the hypertufa mixture and then loosened when the mixture is dry. These can be made on a portable piece of plywood covered by a sheet of plastic. For either mold, use a fairly dry mixture of 1 part cement, to 1 part sand, to 1 part peat moss. Fill the mold at least 1 ½ inches deep. You can trace designs or place decorative stones into the mixture at this point. Let the stones dry, remove them from the molds, and then cure for several weeks before walking on them.
To make a birdbath, you can use a plastic pot saucer or a trash lid or any other form that has the desirable shape. Cover with the plastic liner, fill with a fairly dry mixture and press firmly to shape of the mold. Cure and weatherize as you would a hypertufa container.
To create a water basin, use a small container (about 12” x 13”) for the mold. Line with plastic, and then form the bottom and walls at least 3 inches thick with a rounded inner opening. After drying, weathering, and curing, sink the basin about 2/3 of its height into the ground and fill with water.