First here is a definition
Hypertufa From Wikipedia, the free encyclopedia
Hypertufa is an anthropic rock made from various aggregates bonded together using Portland cement.Hypertufa is intended as a manufactured substitute for natural tufa, which is a slowly precipitated limestone rock;being very porous, it is favorable for plant growth.Hypertufa is popular for making garden ornaments, pots and land forms. Hypertufa is relatively light compared with terracotta or traditional concrete and can withstand harsh winters, at least down to -30 °C (-22 °F). Hypertufa was invented for use in alpine gardens. Alpine gardeners formerly used antique animal watering troughs, which became rare and expensive.
I would also like to add making hypertufa can be fun and it can also be hot ,sweaty work.The temperature must be above 50 degrees for the cement to cure, so this is a warm weather project or moving you project into a heated building.
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Step 1: Making Your Mold
In this Instructable we are going to learn about sand mold. in the first example I made a box out of plywood which has no top or bottom. I got a square of plywood larger then the box and put it on the bottom.I the put in a egg shaped piece of plastic ,large side down (from a microwave egg cooker). I then packed it with wet play sand which is fine.For these it doesn't matter but if your doing anything with some detail you'll want a fine sand. I then put a piece of plywood on top and flipped it upside down.The removed the mold and lined the impression with a plastic bag.I like using plastic bags because they wrinkle and leave texture.The second example is is
some plastic bowls and cups I found at the dollar store for 2 dollars. I got a plastic dish tray ,put a garbage bag over it and filled it with wet sand.Then I pressed in the bowls. Since the bowls where a little flat on the bottom I then found a ball and smuched it (Yes smuched is a word ) around. With the ball in the hole I then packed down the sand around the edges.I then line the holes with plastic bags.For the bases I use a variety of cups and cones lined with plastic bags.
Step 2: Mixing the Tufa
Mixing the Hypertufa
Supplies Portland cement type 1/2, peat moss, bag of sand,gloves. I prefer play sand but a medium sand will probably be stronger. I've been making tufa for over 25 years,anything from pots to large sculptures .There aremany different recipes out there but this is the one I always used. There are many that call for vermiculite and perlitewhich is fine but the sand gives it strength,although it also adds weight.The formula is 1 part cement ,1 part sand and 1 part peat moss. For larger sculpture you can add acrylic admix ,nylon fibers for extra strength and mesh and rebar frames .
I use a variety of cans to measure .I also write down what Iuse for future reference. For example 1 coffee can (1 each of materials) = 1 small mushroom and base.
I first mix the sand and peat moss together, picking out the pieces of stems and twigs out of the moss. Then I mix in the cement. It probably helps to wear a mask. Then make a well in the middle and add the water .Be careful not to add to much. Add some and mix and then add some more till you get the right consistency. You do not want it to wet !! Just enough so when you squeeze a handful it will hold its shape. you don't want water running out.The wetter it is the weaker it will be.
Step 3: Forming the Tufaroom
I then take a handful and press it into the bottom,about an inch thick. Then using a handful at a time ,I start going around the mold pressing the tufa together,using my thumb to press down on the edges. I then take a already finished base in a plastic bag and push it in the center .Then I run my fingers around the top and smooth it out.Then I fold the rest of the bag into the mold to seal it and let it sit for 12-15 hours or more till it's firm enough to handle. But be careful it's still fragile.
The large mushroom was done with a commercial mold.Started the same as the small ones but about a quarter of the way up the side ,a ball was placed in the mold and handfuls of the mix where place around and then tamped down with a piece of wood.
Step 4: Trim and Cure
Now gently pull up the bag so you don't upset the sand to much .I then smooth the edges using a big file with a rasp on one side or a small trowel. Be sure to clean file with wire brush. Then I wrap it up in the plastic bag and let it sit for at least week to cure. This is the minimum.The longer the better. Then take it out of the bag and it will take about a week to dry and turn light gray.I didn't feel like waiting tp weeks so the small Tufarooms in the photo are not dry yet.
Step 5: Large Sculpture Examples
These were made using rebar and a mesh they use for applying stucco to walls.The mesh is a pain to work with.
Runner Up in the
Stone Concrete and Cement Contest