Using Hypertufa

Once a batch of hypertufa is prepared, it can be used in several ways. The most common method is to use molds or forms. The hypertufa is applied to the mold or form and allowed to dry. When the mold is removed, the dried hypertufa retains the shape of the mold.

A common method of molding hypertufa is to construct 2 boxes, one slightly smaller than the other so it fits inside with 3/4" to 1" clearance on all sides. The inside of the larger box is lined with a plastic drop cloth available where painting supplies are purchased. The plastic assures easy removal of the mold later. The hypertufa is applied in a 1" layer to the bottom of the inside of the box. It must be pressed firmly to increase the strength of the final container. Drainage holes are added at this time. The smaller box is covered with a plastic drop cloth and inserted inside the larger box on top of the hypertufa. The spaces between the sides of the boxes are filled with hypertufa (Fig. 9). A wooden dowel can be used to pack the hypertufa. No voids should remain in the sides. The mold is covered with plastic and allowed to cure for a couple days.

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Figure 9. A box within a box can create a form.

After the initial curing, the mold can be removed for reuse by pulling out the inner box and flipping the outer box upside down, allowing the hypertufa to slide from the mold. Use caution at this stage because the hypertufa is still soft and can break. A natural look can be obtained for the container by removing sharp corners with a wire brush. Be sure the drainage holes are not plugged. If they are, they can be opened with a screw driver. The container is now ready for final curing.

An alternate method is to use a single box or other suitable object as a mold. Buckets, nursery pots, and StyrofoamŪ coolers all make suitable molds. The mold is set upside down on a suitable, sturdy work table. It is covered with plastic and the hypertufa is applied to the mold. Firm pressure is used to compact the hypertufa and stick it to the sides of the mold. Begin at the side closest to the work surface and progress upwards. Apply the bottom of the container firming it to the sides. Be sure to leave drainage holes in the bottom. Loosely cover the container with a piece of plastic and allow to cure for a day or two before removing the mold (Fig. 10).

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Figure 10. A hypertufa planter after removal from mold.

The single box or pot method can also be used by placing the mold right side up on the table and lining the inside with plastic. The hypertufa is applied to the inside of the mold instead of the outside. The mold can be lined with bubble wrap or similar material to provide interesting textures to the finished product.

Stepping stones, lightweight rocks and similar garden art can be constructed by forming a mold in the ground. A hole is dug slightly larger than the final desired shape of the object. The hole is lined with damp sand and then filled with the hypertufa mixture (Fig. 11). When constructing stepping stones or rocks, interesting effects can be added by pressing leaves, flowers, fern fronds, or small pebbles or tiles into the wet hypertufa. The pebbles or tiles will remain, but the plant pieces will be removed leaving their impression in the surface. The hypertufa is allowed to cure for a couple days before removing from the ground. Excess sand can be brushed off and the object is ready for further curing.

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Figure 11- A simple form for stepping stones can be made by digging a hole in the
ground and lining it with damp sand before filling with hypertufa.

Instead of using removable molds, hypertufa can be applied to a form, completely covering the form (Fig. 12). The hypertufa is allowed to dry with the form inside where it remains to add rigidity and strength to the container. StyrofoamŪ coolers are especially adaptable to this method.

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Figure 12. Hypertufa can be applied directly to a form, completely
encasing the form, and allowed to dry.

Hypertufa does not stick easily or permanently to objects like wood or StyrofoamŪ without proper preparation. Before use, the surfaces to which the hypertufa must stick are prepared by painting them with a bonding agent. The bonding agent, available with cement supplies, resembles white glue and allows the hypertufa to grip the surface. It is applied to clean surfaces with a paintbrush and allowed to dry to the tacky stage or beyond. Once tacky, the hypertufa can be applied to the surface.

Foam coolers make excellent trough gardens. The foam inner core adds additional insulation to protect the roots from rapid temperature changes. Construction begins by removing the lid if one is attached and drilling drainage holes in the bottom. A 1" wood spade used at low speed can be used to drill the holes. High speeds will cause the foam to break off in chunks resulting in a ragged hole.

The cooler is turned upside down and placed on a sturdy work surface. A bonding agent is painted on the bottom of the cooler and approximately up 1/4th the way on each side. As the bonding agent dries, a batch of hypertufa is mixed. When the bonding agent becomes tacky, the hypertufa is applied like plaster to the bottom of the cooler. The hypertufa layer should be about 3/4" thick. The layer should be uniform and level. It is also applied over the corners of the bottom, progressing up the sides of the cooler 1" or 2". The drainage holes are lined with hypertufa but care should be taken not to close up the holes. At this stage, the entire cooler is covered with plastic and allowed to set up overnight.

After drying overnight, bonding agent is applied to the rest of the cooler inside and out. The bonding agent also should be applied to the surface of the dried hypertufa where the fresh hypertufa will be applied. Just as cement will not stick to StyrofoamŪ, it also will not stick to dried cement.

The cooler is placed right side up and hypertufa is applied to the surfaces beginning with the outside where the previous application left off. Rubbing the hypertufa into the joint will make an invisible seam. The entire outside is coated with a 3/4" layer followed by the inside. When coating the inside, cover the bottom first (taking care to keep the drainage holes open), followed by the sides. Finally, the rim of the container is covered. After the application cover with plastic and allow to cure for a day before final curing.

Hypertufa has the consistency of modeling clay and can be treated as such. Garden objects can be sculpted into various shapes while moist and then allowed to dry. After final curing, the object can be placed in the garden as landscape art.

Gardening with Hypertufa

Final Curing and Aging

Horticulture Projects