Making concrete balls

After seeing industrial geometric accessories for the home and garden I wanted to make some for myself.  They are really easy and I'm sure you'll enjoy working with concrete too.  The possibilities are endless!  Thanks!
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Step 1: Getting organized

Picture of getting organized
Gather your supplies and tools together.  Tools include: safety glasses, rubber gloves, leather gloves, a hammer, old newspaper, a scoop (old yoghurt container).  The safety glasses and gloves aren't in the photo 'cause I'm wearing should too.  And, you should also be wearing closed toe shoes.

I also had a garbage can lid which made great trays for working - you'll see it later photos and most importantly, you need an assortment of forms to mold the concrete.  I also had a bucket of water for rinsing.  

The forms that I uses were salvaged glass light shades.  I had four different sizes and had them nearby and ready to use.   Materials include 'Quikrete' concrete mix and water.
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notimeoff made it!1 year ago
If you want to make a Really big one!...Go to your local craft beer bar and ask them for a empty and depressurised "Keykeg" it plastic ball in a box. remove the ball from the box,cut the top off ( Only if it is depressurized !!!!!!!) with a hacksaw and fill it, then just cut away the plastic "keg"
Here is what i do for fun with "Keykegs":

are these keykegs usually free?

hohum1 year ago
i am not a chemist-''alkaline solution'' could another chemical be added to this, to make the solution less injurious?
bcavaciuti hohum2 months ago

Yes anything acidic really...but it isn't really necessary as it wont be too bad in small quantities. Think of the amount of cement and concrete builders wash off and so you can guess that this tiny amount will really make little difference. Also is not hugely harmful to you but obviously don't be stupid and ruin your soils chemical make-up by chucking it in the flower beds. i would just wait until you are sure all the cement is set then pour it into the sewer drain (not down the toilet though). It would be easier just to put it in a patch of ground that you don't see like behind a shed or something.

firehorse (author)  hohum1 year ago
maybe, but I'm not a chemist either...maybe someone else will pipe up
Citrus juice or any other kind of acid will neutralize the alkalinity. Add until it stops reacting strongly.
Gardener75 made it!3 months ago

I made these and they are great. Surprisingly easy and straight forward. I used a tote full of potting spoil to dry them and dabbed the tops with paper towel periodically. These can be fragile! I broke one, but made the best of it(it had been a couple hours). I brushed it with a wire brush after about 20 hours and smoothed the cracks, which ended up showing the aggregate more. Happy accident, love this look too. To get a fountain run a copper pipe(any sturdy pipe, really) in the mold before pouring the concrete. Large enough to run a pump hose through when done.

tw2sheds11 months ago
For a round shape, you could use perhaps a plastic child's ball from a dollar store or yard sale, if it would regain its shape after having a hole cut in it and being filled with concrete.
fretted1 year ago

NEW plastic mold half sphere 4" W concrete plaster mold

NEW plastic mold half sphere 8" W concrete plaster mold

VIP1681 year ago
thanks for sharing this, i really appreciated it .
jmDCI1 year ago
I've actually done these before, and what I found to look nice is if you take a large leaf with relatively pronounced veins on the bottom, and you put it in the ball (some leaf crumpling required) with the veins facing in, then you pour in the concrete. When you break off the glass and peel off the leaf, a leaf impression will be left on the ball (as long as no concrete gets under the leaf).
firehorse (author)  jmDCI1 year ago
that would be a nice embellishment, thanks!
papito21 year ago
Nice Project. I would suggest replacing the glass by plastic/acrylic ones; you could cut them in half and use as re-usable negative molds. I will try that myself.

Thanks for sharing the project.

ArticAkita1 year ago
cool!!! now I want to fix up some of my own now! what a neat easy idea & I love this!
Nick705871 year ago
I've been thinking of doing something like this but cannot find a large enough sphere for my purpose. I'm curious, do you have any thoughts on where to find larger spheres that are strong enough to handle the weight of the concrete? Something about 24" in diameter?
firehorse (author)  Nick705871 year ago
what size are you think of making? Solid concrete balls are heavy!

I've also got a book on concrete decorations, including instructions on making hollow concrete balls (with chicken wire mesh). It kind of looks like paper mache with concrete.
I was thinking about 24" diameter for some lawn decorations. I thought about using some salvaged naval buoys but they are still too expensive. Maybe one of those exercise balls reinforced with fiberglass would work. Or I could just make smaller lawn ornaments.
You could use cellular concrete to keep them light.
I make foam cement down to about 20-25 pounds / cu ft.
using a foaming agent .
Impress the girls playing catch with your concrete balls.
Or you can easily make them so they float.
Concrete balls that size would weigh about 630 lbs. after curing. Vermiculite concrete is said to weigh 15% of what normal concrete weighs, and that would get you down to 94 lbs. If I were you, I'd coat a 24" exercise ball with expanding foam insulation (a.k.a. "Great Stuff") to about 8" or 10" thickness, except around the nipple. Build a 30" plywood box, and trim the foam so that the ball fits inside tightly, with the nipple-side up. Cut away the ball at the nipple. I'd either hang the ball from the nipple somehow, or attach the nipple loosely to a piece of plywood so it's at the bottom. (It's not critical, as long as the area around the nipple stays uncoated.
Will the foam melt the ball? Will the foam stick to the ball long enough to expand around it? Will differential expansion distort the ball? I dunno.
firehorse (author)  Nick705871 year ago
I would think that 24" diameter forms would take an awful lot of concrete and would be extremely heavy.
Get a big cheap plastic ball and cut a hole in it. Cut it off when the concrete is set. If you cut the hole so that there is a piece left for a hinge, you might get the "sprue" to be spherical rather than flat.
I've seen a few molds for sale online for making "Atlas stones" for strongman training. They're usually thick plastic hemispheres that bolt together, with a hole in top for pouring. The ones I've seen are pretty expensive though, so if anyone knows of a cheaper alternative, that'd be great.
mrpesas1 year ago
How heavy are they when done? I was thinking they might be a good door stop for my classroom.
bo88y mrpesas1 year ago
It would be good to have a large flat spot on the bottom for that application. An 8" ball would weigh about 23 lbs. School kids can do a lot of damage with a 23-lb. ball rolling around. And they'd be tempted to roll it around, if they could.
The volume and the weight increase with the cube of the radius.
bluumax1 year ago
There's an instructable I saw a while back that uses light bulbs to make coat hangers, I thought they looked pretty nice too.
I wonder how well the expansion stuff would work, it could make it easier if it breaks the glass off or expand too much and trash the metal screw contact...
paqrat1 year ago
Interesting instructable. I wish you had come up with a way to make them that didn't destroy light fixture globes.
bobalbury1 year ago
Love your creativity.
I wonder if a massager would help eliminate some of the voids, if you didn't want any?
For the last concrete ball that I made, the concrete was pre-mixed and then placed in the form. The finish is substantially smoother. I actually like the rough texture for the first two tries. For other projects and depending on what you like, viibrating the filled form would likely result is a smooth finish.
rverlohr1 year ago
vibrate it and you'll have a smooth finish
you've got brass-I mean concrete balls
gmyers21121 year ago
so essentially, the instructions are, "Find a hollow round thing. Fill it with concrete. Break the thing off. Here's your concrete ball."
firehorse (author)  gmyers21121 year ago
that's essentially it, but you forgot to add work safely, plan ahead for clean up and different ways of mixing results in different finishes.
Work safely is implied, clean up is something I have to do if I want to stay married and though there are many ways to mix concrete, this is one correct way. Something you may consider, before you let the concrete set up, take a stick or a plunger and "vibrate" the mixture to reach a more homogeneous consistency.
lclaiborne1 year ago
Wonderful! Running out for glass shades...

Balloons won't stand up to the weight of wet concrete trying to slump. You need a rigid mold.
eyebot1171 year ago
I wonder if anyone has tried using balloons for the concrete molds...
jsan6181 year ago
I would like to use the Idea to make a the ball spin via water on a pillar. I ha a small desktop that uses a small water pump. Do you or any readers have suggestions on rounding to opening? Over fill and sand it down i guess. I have no concrete experience other than post holes.
jsan6181 year ago
If you reread the first page picture annotations, Wet gives smooth finish, dry is rough finish. He likes rough finish
dreamers1 year ago
I haven't tried it yet, however thank you for your idea. I love it.
wcable1 year ago
before breaking wrap that newspaper loosely over the top several layers thick then hit with the hammer, this is better protection for you and even easier clean-up.
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