Hypertufa Spheres

Hypertufa half-sphere.

We are still recovering from the plumbing disaster, so I haven't been in my studio.  However, the plumbing disaster has spurred a craft project in a new area: Hypertufa.   I have had an interest in working with the stuff for a while, but had not done so because I would have had to purchase some concrete working items.  Hypertufa (pronounced hyper too fuh)  is a mixture that is similar to concrete, but much lighter.  It is made from a mixture of Portland cement, Pete moss, and Vermiculite or Perlite.  It dries as hard as concrete and is frequently used in making garden ornaments and planters.

Same item, just flipped over.

Field 4-27-2014

How I came to be working on this project in the middle of a disaster recovery is a bit of a story.  I have been wanting to work on a paper mache' project in my studio for some time and was not having much success with the way I was working on it, so I decided to purchase a spherical mold.  I found a half-sphere mold for concrete on sale online at Lowes.  At about the time that I purchased the mold, we had to purchase a concrete mixing tub because we were replacing concrete where they had jack hammered up the floor across two closets, the master bedroom, and the laundry room of our home to repair a plumbing problem.  While we were purchasing the concrete and mixing trough, Bill asked if I wanted to purchase the items we would need for the hypertufa.  So I said sure.  And that is how things got started on this project in the middle of all our home repair project.  It was a diversion to keep us occupied while waiting for the concrete to dry.  Watching concrete dry is akin to watching paint dry, only worse.  It takes about twenty-eight days of curing before we can put down the new laminate flooring.

Field 4-13-2014

I'm documenting my experiences with hypertufa in case anyone is interested in using it to make some garden spheres.  Here is a three question test to see if you really are interested enough in the project to make it worthwhile to go to all the expense.  1.  Would you enjoy vigorously hoeing in your garden while wearing a face mask and eye protection? 2. Do you have a tolerance for garden tools that do not wash completely clean?  3.  How much weight can you lift?  If the first two answers are no and the third answer is not a lot of weight, you might want to hit the reject button on this project now.  If you are still interested, read on.

The Portland cement comes in 90 pound bags.  The Pete Moss is pretty heavy as well.  The vermiculite or perlite is not heavy.  You can probably  have someone load it at the store, but plan on how you can deal with it once you get home.  My husband moved it for me.  My Plan B was to roll it from the edge of the van into a wheelbarrow.  My Plan C was using a bucket and shovel.  You also need to plan on what to do with the rest of the cement, because you are only going to use a small portion of the bag to make a sphere.  The cement comes in a plastic coated bag.  Once you open it, humidity will start to harden it.  We used to buy laundry detergent in forty pound buckets.  We saved the buckets, because you never know when you will need a giant bucket.  I lined some buckets with plastic trash bags, filled them with the remainder of the cement, tied off the bags, and sealed the container with it's tightly fitting lid.    It was either that, or buy a whole lot of concrete molds.

There are a couple of hypertufa recipes out there.  The basic recipe is one part of each: Portland cement, Pete Moss, and either Vermiculite, or Perlite.  The other commonly used recipe is one part of the cement to 1.5 parts of the other two ingredients.  Some people just use water to mix it.  Others use a mixture of water and acrylic ad mix.  Some people add polyester or nylon concrete fibers, but most people say they aren't necessary.  That is a distillation of most of what is on the internet about hypertufa.

Aside from the recipe, a trough, and some tools to mix with, there are a few other things you will need.    Unless you have a workshop dedicated to mixing cement or plaster, you will need to do this outside.  A dust mask and eye protection are essential.  Portland cement is a very fine powder.  It is going into the air while you are measuring it and dumping it into the mixing trough; the slightest breeze will send it wafting up into the air. You will need some waterproof gloves.  Thin latex or vinyl gloves rip easily, so I recommend something like the rubber gloves available in the cleaning section, such as Playtex gloves.  You will also need a release agent for the mold.  Many web sites recommend the original Pam cooking spray.  I used it and it works great.  (A word to the wise:  In some other craft projects I have read that the crafter had used an off brand cooking spray and had not had good results.  The binding agents vary between cooking sprays.  While it may not matter in cooking, it does seem to have an effect on craft projects.)  You also need a board cut to the size of the outer perimeter of your mold, and some plastic trash bags.  So armed with this information, we set about on our hypertufa experiment.

I did not have a plywood board that I could cut to size to cover the mold while it was being flipped over (more on that in a minute).   So rather than purchase a whole sheet of plywood when I only needed a small piece of one, I made a board out of multiple layers of cardboard layered across the grain.  Laying them crosswise to each other added strength.  This cardboard came from a heavy moving box used for packing dinner wear.   The edges of the stack were taped with duct tape, and then the whole thing was covered in duct tape.  I slipped this support into a plastic bag to help keep it dry and tied it off.  Plastic was needed not only to keep the support dry, but also because Hypertufa will not stick to the plastic.  This support worked as well as a board, and was lighter than a board. 

First off, I measured the volume of the half-sphere mold. It held eighteen cups of water.  So I thought I would have the amount figured out of what I needed in materials.  Wrong!  The moss and vermiculite have a lot of air space between the granules.  When the liquid was added it collapsed the air spaces and the volume decreased.  Secondly,  the space between not enough water and too much water is just a hair.  You have to mix in a little liquid with the cement mixture, move it around with a hoe to mix it, then add more water until it is just right.  Of course on my last water addition it was a case of "oops, too much".  So I added more material in each proportion until I no longer had a soggy mud.  As it turned out, it ended up working out that I had just enough to fill the mold once I added the extra material.   For the record, mixing hypertufa is almost as strenuous as mixing concrete.  The material is slightly lighter, but mixing hypertufa is a lot of work.  I was sore the next day.

The mold was sprayed with the Pam Original cooking spray and filled with the hypertufa mix.  The cardboard support with the plastic bag over it was placed on top of the mold, and the mold was flipped over.  (You flip the mold so that you can remove it the next day without disturbing it too much.  It also gives you a flat bottom when you are mortaring the halves  together.)  Then this whole setup was slipped inside of another plastic trash bag, tied off and left for 24 hours.  After twenty-four hours, I removed the mold.  It slipped off easily.   Then the ball is left inside the sealed plastic trash bag for a week.  After that, it can be set outside to dry the rest of the way.   It takes a long time for these half spheres to dry completely.  It is still very wet, even though it has been outside for a week.

In theory, once you removed the mold, you would cast the second mold they next day.  However, we were going out of town, so I could not cast the other one until after we came home.  I did not buy two molds, because of the cost.  The mold I purchased as $29.95 and free shipping.  It is a sturdy hard plastic mold.  I also found a less expensive silicone mold for $15.00, but by the time you paid the shipping costs, bought sand to support the mold and a container to hold the sand, you probably spent close to the same amount.  Anyway, once both pieces are cast and dry, you put them together with thin set mortar mix.  I'll blog more on that once I get that far.

I feel I should also mention the clean up, because that is a lot of work as well.  The concrete we used to patch the floor washed out of the mixing trough much better than the hypertufa.  It may be that the trough was smooth initially, but after it gets nicks and scratches from the mixing implements, things change.  The vermiculite from the hypertufa got into those scratches, and vigorous scrubbing would not remove it all.  We finally settled for getting it as clean as we could.  The concrete also dried on the tools to a certain extent.  The crevices around the handles will never be the same.

Right now, I have one half-sphere setting outside, and the other half-sphere ready to come out of the mold.  I will blog more on my hypertufa sphere once I get it put together.  I want to do some more reading to see if anyone has posted on if or how long they let the pieces cure before they mortar them together.

Today's blog also has a photo for my field project.  I did not take a picture last week because I was out of town.  I am also posting the previous picture so you can see how much difference there has been in two weeks.  So far the farmer has not plowed the field.  The neighborhood is speculating as to whether he is waiting until the frost date, leaving the field fallow, or just not planting anything because he has put the field up for sale.  Time will tell.