Hypertufa Spheres- Part 3

Cast as half-spheres and mortared together.

Child's ball was used as a mold.

Today I'm posting the first photos of my Hypertufa (pronounced Hyper-too-fuh) spheres.  I've learned a lot from making the spheres, and I hope you can learn from my experiences.  It was not a difficult project, but there are some things that are worth knowing before you get started.  Before beginning this project I had read a number of articles and posts around the web.  I found a bit of useful information on each site, but not a site that had all the information in one place.  I hope that people who view this site will be able to get a lot of the information here that I had to search all over the web for.  And of course, I've learned from my mistakes, so there is always something to add in that area.

The first picture is of the ball made from the ten inch diameter half-sphere concrete mold.   It is cast in two parts and then put together using thin set mortar.  The Hypertufa mix I used was 1 part Portland cement to 1.5 parts Pete Moss, and 1.5 parts Vermiculite.  The mold is sprayed with Pam cooking spray for a mold release.  I mixed this mixture with acrylic liquid Mortar Ad Mix and water.  The first half-sphere had a little too much water in it.  It allowed a little of the cement mixture to leak out underneath the mold when it was flipped over, resulting in a slight lip forming on the ball.  I could have removed it easily using a putty knife or razor scraper if I had dealt with it after it had sat in plastic for a week.  At this point, I'll probably remove it with an Angle Grinder.  One of these days I'll get around to it. 

The Hypertufa mixture is much lighter than using cement.  On one website, someone had calculated the weight of this ten inch mold using concrete.  That ball weighed in at ninety pounds.  I weighed my Hypertufa ball yesterday.  It only weighed twenty pounds.  That is a workable weight.  The half-sphere mold would only weigh ten pounds, so it is easy to flip it over.   A twenty pound ball is easily lifted.

You can see a center line where I stuck it together with the Thin Set Mortar.  I count this as one of my mistakes.  I purchased a bucket of premixed Thin Set Mortar.  I thought it would be easier to use it on two counts.  First, I would not have to find another bucket to store the rest of the remaining mortar.  At this point, I would have had to purchase one.  The second consideration was that by using premixed Thin Set Mortar that I would have less clean up, as I would not have to scrub out the mixing trough.   Well, there was less clean up because I did not have to clean the trough, but using that premixed mortar was a real mess.  It had so much plasticizer already mixed in it that the mortar was like tar.  It was sticky and stringy and difficult to use.  It did not clean off the ball well.  (One of the web sites had said that the mortar
wiped off easily with using regular tissues.  It might have if I had not used this plasticized premixed stuff.)    Because the mortar mix was so sticky, I did not do the best job of getting the rim completely smooth.  The mortar was sticking to the ball, everything I had on, and everything it touched.  I finally decided to quit while I was ahead.  I had used a silicone spatula to spread the mortar and the stuff did wash off that easily.  However, I ended up throwing my rubber gloves away.  The mortar would not wash off of them at all.

The ten inch diameter mold is a true sphere shape.  It rolls very easily.  When you get ready to mortar the halves together, make sure that you have the half-sphere braced well so that it won't be rolling around while you are adding the other half.  Because it rolls so easily, the slightest imbalance is going to cause the top half to slide around on top of the mortar.  I had to keep moving it back into place until I had the ball balanced just right.  In other circumstances, I would probably have done a better job of it.  In the middle of the recovery from the plumbing disaster that befell my home, some of the things that I might have used to make the job easier were inaccessible and I was working in less a than ideal place.

As it is, this ball could stay outside all year.  I've read that if you treat it with a white vinegar and water solution to remove alkalinity that it could be encouraged to have moss grow on it.  This ball could also be used as the base of a mosaic gazing ball.  I would recommend bringing it inside in freezing weather if you add tiles and grout.  Or, the ball could be painted. 

I had some extra mix left over, so I experimented with another method of making a Hypertufa ball.  This ball used a child's ball as a mold.  I purchased this ball at Walmart.  Right now they are everywhere, but as soon as they sell out you won't see anymore for months.  So buy them now if you want them.  I don't have a picture of the ball itself, but it was the size is about eight inches in diameter when purchased, but the material is stretchy, so after the air was let out it became significantly smaller.  It made a ball somewhere between five and six inches in diameter. You cut a hole in the top large enough to get your hand into so you can add the hypertufa.  (Note, once you cut the ball, it will reduce in diameter. as it deflates.) Spray the inside of the ball with Pam cooking spray as a mold release.   Add a little hypertufa tap it down firmly.  If it is not firm, it will leave air pockets that are voids in the ball.  Fill it full, seal the ball in a plastic bag.  On the internet, it said to leave the ball nestled in sand to help keep it from flattening out on the bottom.  (See last Sunday's blog post for a picture of the ball nestled in a bucket of shavings.)I did not have sand, but I had wood shavings, so I used that instead.  For the most part, it worked.  The bottom was slightly flattened, but not so much that you would notice without a close inspection.  The opening at the top was more problematic.  It was hard to get it completely rounded. 

I was concerned that the  top of the ball would stick into the concrete mix and not come off, but that did not happen.  What did happen was that the ball formed a slight peak at the top.  This had to be shaved off once the ball came out of the mold.  You can still see a slight circle around the ball in the second picture.  I used a putty knife to shave the excess concrete from the ball. 

Again, there is something to be learned from a mistake.  From my reading on the internet, the instructions for making these balls said leave them in the mold for one day and then remove the mold them and let them sit in plastic for a week.  That is exactly what I did for the 10 inch diameter sphere mold.  However, with the mold created from a child's ball, that is not how it worked out.  Due to pouring rain and trying to get things back into some semblance of order after the plumbing disaster (see previous posts for info on that), this mold set in the plastic bag for a week.  I feared that this part of the project would be a total loss.  As it turns out, it was not. 

Once I was able to get to work on the mold, I cut into the top edge of the rubber ball.  Once started, the ball pealed away in a spiral around the concrete ball.  The ball was still quite moist from being sealed in a plastic bag.  I was able to use a putty knife to pare down the part of the ball that was above the top of the ball mold.  It was firmer than if I had tried to take it out after only one day.  I count this as a good thing, because some people had said that sometimes their balls fell apart when trying to remove them from the mold.  So, this was a happy accident that has added something to the conversation.   Even after leaving it in this type of mold for a week, it was no problem whatsoever to unmold it or to shave down the raised areas. 

Due to the mold having to sit on something, it is not a true sphere. It is somewhat flattened on the bottom.  However, it is not so badly flattened that the casual observer would pay much attention to it.

This post is getting long, so I will blog about the other experimental molds on Sunday.