One basic recipe can be used as the starting point when working with hypertufa. It can be altered to provide different textures and strengths to suit the individual project. A general guideline is that the more portland cement added, the stronger the final object. However, too much portland cement increases the weight of the object. Good strength is achieved with the following recipe:
1 part portland cement
1 part screened peat moss
1 part perlite OR 1 part vermiculite OR 1 part sand
Dye to color the mixture
Fiberglass fibers or acrylic hardener
All measurements are made on a per volume basis, not per weight basis. For example, a mixture would be made of 1 cup of portland cement, 1 cup of screened peat moss and 1 cup of perlite, not 1 pound of each. If mixed on a per weight basis, the mixture would contain too much peat and perlite compared to portland cement because these ingredients are much lighter in weight than the portland cement.
Peat moss usually is available in compressed bales of varying sizes. It will break apart into clumps, and contains small sticks and other organic materials. For hypertufa use, the peat moss needs to be passed through a screen to break up the clumps and remove the other materials. If these other materials are allowed to remain, they will cause voids in the final object as they decay and fall out. Peat moss is easily screened by passing it through a piece of 1/4" hardware cloth. Hardware cloth is a fencing material made of galvanized wire. The wire is woven together to form squares of different sizes. The 1/4" size will remove most of the debris and break up the clumps. The ½" size allows too much to pass through.
When mixing a batch of hypertufa, begin with the peat and the perlite/vermiculite/sand (Fig. 4). Thoroughly mix equal volumes of both ingredients to obtain a homogenous mixture Fig. 5). Add an equal volume of portland cement, and again mix together thoroughly (Fig. 6). The mixture will be extremely dusty.
|Figure 4. Begin by mixing equal volumes of peat
with either perlite, vermiculite or sand.
|Figure 5. The first 2 ingredients should be
mixed before adding the portland cement.
|Figure 6. The portland cement should be completely
with the other ingredients before adding water.
If desired, fiberglass fibers can be added with the portland cement. They will be difficult to mix and instead will tend to clump together. The amount added will be between ½ and 1 part of the volume of the other ingredients.
Water is added slowly to the mix. The final volume of water added may be between 0.5 and 0.8 part by volume. The exact amount of water added will depend on the moisture content of the peat moss and/or sand. The desired consistency is that of modeling clay (Fig. 7). Too much water will make the mixture difficult to work with. If the mixture is too watery, additional amounts of portland cement, peat moss and perlite/vermiculite/sand must be added. Once water is added, the fiberglass fibers will disburse more easily through the mixture. After mixing the ingredients thoroughly, allow the hypertufa to stand for about 5 minutes. The peat moss will absorb some water during this time and additional water may be required to maintain a workable consistency.
|Figure 7. After mixing, hypertufa should have the
consistency of modeling clay.
Dyes and acrylic hardeners are added at mixing in liquid form. The desired amount is mixed with water and added to the dry ingredients before the plain water. Do not add the dye or hardener without first mixing with a small amount of water, because it will be too difficult to distribute through the mix.
Any suitable container can be used to mix a batch of hypertufa. The container should be large enough to mix up enough hypertufa that can be used within 30 minutes. Beyond 30 minutes the hypertufa mixture begins to set up. Five-gallon buckets and wheel barrows are often used. A large, shallow container allows for easier mixing than a tall, narrow container (Fig. 8).
|Figure 8. Hypertufa is easier to mix in a large,
container than a tall, narrow one.
Mixing and using hypertufa is a messy process. Wear old clothing and work in an area than can be hosed down once the project is complete. Clean any equipment and mixing containers immediately because the cement will be difficult to remove once it dries.
Gardening with Hypertufa
Final Curing and Aging