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Do-it-Yourself Stone Pots: Hypertufa


Do-it-Yourself Stone Pots: Hypertufa

By Ken Schultz

For our January meeting we hope that you will join in making a Hypertufa pot that you can use for the forest planting that we have planned for our April Meeting. Pots large enough for a forest planting can be quite expensive. A hypertufa pot that you make yourself can be an economic alternative.

What is hypertufa you asked? You may have seen troughs made for alpine or miniature conifers that when planted are fairly expensive. Even the empty trough pots for these uses can be expensive at your local garden center. However, the cost is in the labor. If you are willing hypertufa pots can be made for a few inexpensive ingredients; Portland cement, peat moss and mason's sand. Some formulas call for the use of perlite rather than sand to make them even lighter, but some strength is sacrificed in doing that.

The Club will bring pre-mixed Hypertufa to the meeting. Tobe Conn offered to provide some latex gloves, as cement can be very drying to your hands. What you will need to do in preparation is to think about the style of your pot. Look through your bonsai books for do-it yourself projects that show making containers. Your container can be square, oval, irregular, island shaped, it can have a stream channel or a cave. One book I have even shows putting a water pump in the base and creating a pond with a waterfall. The book features Chinese styles not Japanese. Another book showed making a mountainside. Remember forests grow in a variety of locations.

Will you need a prepared mold to spread the hypertufa mix on? It is possible to spread the Hypertufa mix like plaster over a screen mold. One article suggested using a piece of screen on the bottom to improve strength. Your screen or wire may need to be cut so bring your snips; you won't want wire poking out of the cement when the pot is dry. I have seen dowel rods used for lateral strength while the mixture dries. The sides and bottoms will need to be at least 2" thick for strength. If you are planning to use boxes for your molds the smaller one should be 4" smaller than the larger one to maintain the thickness you need for strength of the finished pot. One thing you should definitely bring is a bucket or plastic dishpan to put some hypertufa mix in to work from like the hod of a brick mason.

You will also need a piece of plywood or tray (some may be available) to make your pot on to carry it home and a piece of visqueen (we may provide) so that you will be able to separate your pot from the board after it dries. The mixture will take several days to dry, especially in cold weather. Actually this is good, because slow drying reduces cracking and makes the pots stronger. You can use short pieces of dowel rod to create drain holes or you can drill the holes with a masonry bit after the pot dries. The holes will need to be about 3//4" to an 1" in diameter, spaced 3"-4" apart. While dry to the touch, it will take a month or two for the hypertufa to "cure" all the way. When it is completely dry it will make a slightly "hollow" sound when tapped. So be patient, this is why the Forest Planting workshop will be April 23. Some of the "tooling" of the surface should wait until your pot has dried for a day or two if you want it to look rougher. If you want a smoother surface you should bring a water spray bottle to wet the material while you trowel it.

The dry color will be cement like. Because of the craggy surface algae or moss can be grown on its surface. If you want a different color - bring some mortar dye to mix in. One ounce of dye per gallon of mix is the ratio. Because cement has a good deal of lime in it, the pots will leach alkaline; this is not good for conifers, azaleas or any acid liking plants. So after your pot cures you have a couple choices. Put it out in the yard to let the elements leach the alkalinity out, or douse your pot with vinegar or a light solution of muriatic acid (4 parts water to one part muriatic).

If you want a rougher surface or you want to "carve" the pot bring tools like a wire brush, chisels, trowels or just a large nail. The hypertufa mix will have the consistency of cookie dough or as one article said - "the consistency of moist cottage cheese." The mixture used to make troughs is a bit thinner since it has to be pressed into a mold.

You should also bring an old dry cleaning bag or piece of plastic to cover your creation on its ride home; that will protect your car and your clothes. While dry hypertufa is lighter than stone or concrete remember that a 15 " square pot will have about 3 gallons of mix, and a wet gallon will weigh about 8 pounds. ~ Ken Schultz

I have seen a variety of formulas - we will probably use one with perlite, and or one with Masons Sand. Also one of the recipes calls for adding 2 cups of Acrylic bonding agent to the water to improve strength

Here's a recipe: Makes a trough 8"x12"x12"
2 parts Portland Cement (30 pounds)
3 parts sieved peat moss (1 cu ft)
3 parts vermiculite, or sand (1.5 cu. ft.) - Mason's sand makes it look more like stone.
1 cup color
1-2 cups acrylic bonding agent (Gardenweb recommended)

Add liquid until it is like stiff cookie dough. - Allow mixture to "rest" 10 minutes after it looks "right".

Here's another: Makes 8-9 containers 12"x14"x6"
1 bag portland cement
1 bag sand
2 cu ft peat moss

One container takes 3 quarts Portland cement, 3 quarts of sand and 6 quarts of peat moss. 1:1:2. For a sandstone texture - change the ratio to 1:1.5:1.5. Add water to a cottage cheese like texture. This one says let it dry for 24 hours then see if its dry enough to handle - and work to give it a stone texture.

Formula #3:
3 parts perlite
3 parts peat moss
2 parts Portland cement
concrete colorant - 1 oz/gallon of mix
one handful of fluffy Fibermesh per gallon of mix

This one says 3 gallons of mix makes a 15" square trough. This one also says to coat your mold with linseed oil as a release agent. However the fibermesh fuzz has to be burned off with a torch. I favor the acrylic bonding agent - I can pick up a few gallons at the Tile store on Morse Road. It makes tile grout and motar flexible so that it resists cracking.

Other tools needed:
Steel chisel, file, or nails to carve with
Mason's trowel
wire brush
Mixing trough
rubber gloves
dust mask (Doc says he has old surgical masks)
dowel or pill bottle to make drain holes.
a dishpan or large pot
plastic drop cloth or old dry cleaning bag to line your mold
chicken wire - 3/4" mesh or screen/hardware cloth - Dan B. said he would have some screening.
spray mister - to keep your work from drying to quickly
linseed oil, or cooking spray
Vinegar will help keep your hands from drying out if you get any on your skin.