Originally developed in Europe during the 1800s as a substitute for heavy stone watering troughs, hypertufa is a man-made version of a natural porous rock known as tufa. This cement/aggregate blend is lightweight and easy to mix, shape and mold. All you need are a reliable recipe, a few basic supplies and some helpful hints from HANDY and you'll be able to create custom garden art for a fraction of what you'd spend at a retail center.
Although many variations of hypertufa recipes exist, all of them incorporate these basic ingredients:
- Binder — Portland cement (which is not the same as concrete mix) holds everything together. For color purity, use white (rather than basic gray) Portland cement if you plan to tint the mixture.
- Aggregate — Peat moss (aka sphagnum) and/or perlite help to keep the object from becoming heavy. Some sand (from a store, not a beach) may be included.
- Liquid — Water (in just the right amount) makes the mixture pliable; it also serves as a carrier for additives such as fortifiers and colorants.
Chemistry is the key to a solid outcome. The general proportions are one part binder (cement) and two to three parts aggregate. There is no measurement for the water because the amount varies depending on the moisture level in the dry ingredients and on the air's humidity and temperature. Add the water (cold is best) gradually to reach optimum consistency (a texture similar to that of stiff brownie batter).
If you're filling an intricately shaped mold, you may need to increase the amount of water to create a softer mix. Just remember that too much liquid compromises the object's strength and may cause the aggregates to settle in layers. Any liquid additives, such as fortifier or colorants, should be blended into the water before you mix the water into the dry ingredients.
Forms and molds
Be sure to have the forms ready to fill before you prepare the mixture. You can make custom shapes and sizes out of 2-in.-thick foam board, or use boxes, bowls, buckets or other sturdy containers. To ensure that the finished piece releases from the form, line the container with plastic or coat the surface with cooking spray. Depending on the size of the project and the finish you want on the outside of your piece, you can pack the wet mixture on the inside or the outside of a container. Another option is to sand-cast a piece (which releases very easily from its sand-bed form).
A mild day is ideal for working with hypertufa because the material will not dry too quickly. Once the piece has set up (after 24 hours), you can remove it from the mold and set it in a damp, cool place to cure for several weeks. The longer the cure time, the stronger the piece will be. By spring, you'll have planters and ornaments that have completely cured and are ready for the garden.
Work outside on a nonwindy day to prevent the dry ingredients from becoming airborne – and to keep the project's inherent messiness out of the house. Be sure to wear grubby clothes, heavy waterproof gloves, eye protection and a dust mask.
- Combine equal parts of Portland cement, peat moss and perlite in a mixing trough or wheelbarrow. Thoroughly blend the dry ingredients before adding the water.
- Continue to stir the mixture as you gradually pour water into the trough. Add water in stages until the mixture holds its shape in a ball. Allow the mixture to set for about five minutes; then stir it again.
- Set the mold container on a flat, solid surface and scoop the mixture into it, packing it down as you go. (A scrap of foam board makes a good tamping tool: It's gentler than a piece of wood or metal.)
- Wrap plastic over the entire piece and place it in a shady spot to dry.
- After 24 hours, remove the form and cover the piece again with plastic to retain moisture and generate condensation. Maintain high humidity (mist water on the piece if needed) and allow the piece to cure for several weeks. A slow, cool, damp cure increases the strength of the finished object -- especially important for stepping stones.
The tufa bowl
You can replicate the shape of a bowl by pressing the mixture along the bottom and sides of a greased or plastic-lined bowl. Form an even thickness of 1-1/2 to 2 in., shaping the piece with your fingers – just like pressing a graham cracker crust in a pie plate. If available, a smaller bowl can be pressed inside the form to help create a more uniform shape and thickness. For a larger finished piece, you can press the mixture over the exterior of the bowl. In this case, the inside of your hypertufa piece will be smooth, and the outside will look more rugged.
With the piece still inside the form, wrap it in plastic and set it in a cool spot to dry overnight. The piece will be firm but still vulnerable, so remove it carefully from the mold. If the outer surface is too smooth, you can create a more rustic look by scraping it with wire brush. Wrap the piece in plastic and leave it in a cool place.
Once you've mastered the basics of hypertufa, the possibilities are endless. Go ahead and adjust the recipe a bit. Be creative with various molds and shapes (lantern, leaf impressions, etc.). You can even play Michelangelo and do freehand sculpting of the wet mixture. Inset embellishments, such as decorative stones, colored glass and ceramic tiles on the surface of the piece. Once the piece is completely dry, you can sand the surface smooth. Become an artist – or tap into your inner child and form a castle that won't wash away with the tide.
Large mixing bin
Portland cement, sphagnum peat moss, perlite, water)
Fortifier (optional) for adding strength, such as in stepping stones
Molds (box, bowls, bucket, bin, sand, etc.)
2-in. foam board and marking/cutting tools
Release agent (plastic bags or cooking spray)
Heavy-duty waterproof gloves
Grubby clothes and shoes
You can form a mold by pressing an object into damp, firmly packed sand. Moisture in the sand is important because it helps to retain the contours that you form and because damp sand will not rob moisture from the hypertufa blend, which would cause the piece to dry too quickly. Here's how to make an impression:
- Pack moist sand into a sturdy container (bin, trough, box, etc.) that is slightly larger than the piece you want to form. (If you plan to move the container before the hypertufa piece is dry, be sure that it is well supported and will maintain its shape when lifted.)
- Press a mold form into the sand, jiggling it slightly as you push it down. Gently lift the mold away and check that the shape's details have appeared in the sand's contours. If not, just smooth and pack the sand; then try again.
- For this method, you need to mix a softer, almost pourable hypertufa blend. Gradually add water until the consistency is similar to soft brownie batter. Carefully scoop the mixture into the sand and lightly jiggle and tamp the container to help the mixture settle into all cavities. Spray a light mist of water on the sand's surface and cover the container with plastic until the hypertufa is set (at least 24 hours).
- When you remove the piece, you can brush off all or part of the sand to achieve the finish you desire. Store the piece in plastic for a few weeks for slow curing.