How to make a Hyper Tufa Garden Ornament
Hypertufa is an interesting material widely used in the manufacture of planters and garden ornaments. It has a natural looking porous look and is easy to mould and shape. It is much lighter than regular concrete. Several additives can be incorporated to change the characteristics of the Hypertufa.
It quickly gets an attractive old mossy look if kept in a damp place.
I wanted to mould a sunburst in Hypertufa to use as a garden ornament.
I had made this mould to make a mask. It was originally sculpted out of clay and covered with white silicone mouldmaking material. It's a fabulous material that makes very detailed and durable moulds. It is unfortunately also a bit pricy. In this mould I covered the original clay pattern with a couple of coats of the silicone then used translucent aquarium grade silicone sealant to strengthen and stiffen the original mould. I then covered the silicone (both mouldmaking material and sealant) with a layer of plaster of paris. This mother mould backs the mould and gives it support when it is used.
I had used this mould for a papier mache mask and for plaster of paris ornament. It has no undercuts and is really easy to unmould.
After cleaning out the spiders and dust I placed it in its plaster mother mould and leveled it. Because hyper tufa does not flow it is not critical to be perfectly level.
Hyper Tufa Materials
There are several recipes for hypertufa. They all have portland cement and sand plus peat moss. Many add perlite or various stones. Some recipe add colour. These colours can be found in stores that specialize in mortar, concrete and brick. Occasionally you can find the pigments in hardware store. Usually pigment is added in powder form. The brown is usually some form of iron oxide and the black is often copper oxide. These should be handled carefully since they are toxic. Cement is quite corrosive and can give you a nasty burn. Its best to use gloves and goggles when mixing. If you are doing a lot, a particle respirator is not a bad idea. These are not awful materials but they can be dangerous if you are not careful
Peat moss comes packaged in compressed bales and can have a lot of little branches and chunks of plant materials. Large pieces should be removed and if you want a fine even textured hyper tufa you can screen the peet moss. In this project I just took out the big chunks. I know this will weaken my figure but that is not important to me.
Some recipes add an acrylic binder to increase strength. This can be found in the cement department of the Big Boxes. It is a milky liquid additive that is used instead of water.
Hyper Tufa Recipe
The Classic recipe for Hypertufa is 1 part Portland Cement to 3 part aggregate. The aggregate will be a mixture of sand, peat moss or sphagnum moss, perlite, rocks, etc.
In this project I am using 2.5 measures of sand, 2.5 measures of peat, and 1.5 measures of cement. I can get away with less cement because strength is not really an issue in this case. More cement and acrylic binder would make a stronger finished piece. Reducing the amount of peat also strengthens the mix.
The amount of water depends on how wet your moss and your sand is. In this case I used 2 measures of water. You would need less if your sand or peat is damp. As you mix, the peat will absorb water so you might have to add more. I like a mixture that will stand on its own and not flow and slump. If I squeeze it in my hand no water comes out.
Before making your final ornament you can experiment and make a few test chunks to see what look you prefer and what is strong enough for you. Let it sit for a few days in a damp spot to develop proper strength. You can then see if the texture is pleasing and if it is strong enough for you.
I had prepared a wire hanger from an old coat hanger. I made several bends in the wire so it would stay solidly in the ornament and not pull out.
Filling the Mould with Hypertufa Mixture
Using gloves I gradually pushed the Hyper Tufa into the mould making sure I did not get any large air spaces. Small bubbles are fine.
It is important to wear gloves when you do this or your skin will get quite raw. Cement is corrosive and will burn you. Keep the cats out of the way too.
Once the mould is filled even out the back so it can lay flat. Pay particular attention that the borders are tidy. The cement will start setting in about a half hour to 45 minutes so you have lots of time to work.
Gently tap your mould to make the mixture flow into any hollow.
You can add reinforcement such as wire mesh or fiberglass in the hypertufa. This is often done if you are making a flower pot.
Placing The Hanger in the Hyper Tufa Ornament
Push the hanger into the back and make sure that the Hupertufa has flowed around and sealed the hanger in.
Resist the temptation to unmould your ornament for at least a day. At first it is quite fragile and easy to break even after the cement has set. Over a week it gets harder and more resistant.
Keep the hypertufa moist for a few days at least since it gradually strengthens as crystal structure forms.
Unmoulding the Hypertufa Ornament
After a few days it is safe to carefully unmould the piece and clean up any flashing. Here I have supported the piece on a flower pot and I'm peeling off the silicone mould. There is a bit of flashing on the edges but otherwise the moulding is good.
If you want to texture or "weather" your piece you should monitor the hardness of the back and when the hypertufa is hard but can still be scratched then carefully unmould and texture. I like to use a stiff brush to smooth out and give the piece a worn look. Use water and go easy. You will be able to brush out pieces of peat and make your ornament look old and weathered. It is still very fragile so be careful.
Before and after light brushing and texturing. The piece as it came out of the mould has a cement glaze on the surface and slight flashing around the edges. After careful brushing it has more texture as peat is exposed.
The more peat you include the rougher and more weathered looking the texture will be but the weaker your ornament will be.
After a while the ornament or flowerpot acquires a patina and starts growing moss and algae. This old moulding of Pan has lived outside. It was very soft and is quite weathered.
It is over 10 years old and has survived with no particular care at all. I don't think I would leave standing water in a hyper tufa pot to freeze in the winter but otherwise it is quite strong.
Before moss and algae will grow the cement will need to be neutralized. It is quite alkaline when it is new. There are many recipes to neutralize the cement and get algae to grow. I like to use a mild vinegar solution and then rinse the ornament. I've heard of people using Yoghurt.
The ornament will gain strength for about a month if kept moist. It will get lighter when it dries. Once dry it can be hung up.