Tutorial ~ How To Make a Hollow Concrete Sphere

Posted by @rcn48 on
Concrete statuary in some of the gardens I've visited has always captivated me. Unfortunately most statuary I've priced is quite expensive and with my tight budget the chances were slim that any of these creations would ever find themselves in my gardens. However, several years ago I was intrigued when I stumbled upon instructions for making "hollow concrete spheres". I was pleased to learn the cost of materials is fairly inexpensive and last year successfully completed my first sphere. I'd like to show you how easy it is and hopefully inspire you to create your own hollow concrete sphere!

Some of you might ask, “what is a hollow concrete sphere”? I had no idea what they were until I read the book: A Garden Gallery ~The Plants, Art and Hardscape of Little and Lewis and saw their magnificent concrete creations. I was fascinated with their unique hollow concrete spheres and after doing some research discovered they're simply a thin-walled sphere constructed with concrete. Displayed in the landscape the spheres can either be planted or filled with water. Now that you know what hollow concrete spheres are let me show you how easy it is to make one and then you can develop your own distinctive style with paint, plants, or decorative accents.

I embarked on my first attempt to make a hollow concrete sphere last summer. With temperatures soaring I escaped to the shade under my deck and in just a few days had completed my first sphere. The steps to make the spheres are simple enough; however, I've been told my descriptive instructions are "lengthy" so bear with me. After all the research I've done before (and after) making my first sphere, I hope you’ll agree the additional information and tips provided will be helpful when making your first sphere.

Choosing the size of your sphereLocation of sphere in the gardens

I always recommend choosing a location where the sphere will be displayed in your gardens, before deciding what size sphere to create. Obviously larger spheres will be more difficult to move but also keep in mind that smaller spheres will sometimes get 'lost' in the landscape.

I used this photo to help determine the size and location of my first sphere. With a rough 'sketch' I was able to quickly determine that my sphere should have an approximate diameter of 16".

Work area

Since most of you will probably be working outside for this project try to choose an area in the shade. Sun exposure and wind are your worst enemies when properly, and successfully, curing concrete. Use a table or anything which helps to lift your work space off the ground. You'll find it's much easier working at this height to prevent bending, stooping or sitting during each session. It's also helpful if your work space has a 360 degree access. This allows you to move around the sphere versus rotating the pot supporting your sphere. 

Estimated time to complete a hollow concrete sphere

The preferred method is to plan a block of 4 - 5 days to complete your sphere. However, it is possible to spread the days over two weekends or more if necessary. You will need to take extra precautions, though, to guarantee the concrete retains moisture during this time to prevent cracks in the sphere between applications of each layer.

LIST OF MATERIALS
   
Materials
  • Inflatable ball
  • Large and small bowl to mix concrete
  • Gloves
  • Dust mask
  • Vegetable oil spray or petroleum jelly
  • Large pot to support ball
  • Large trash bag and tape to cover sphere
  • Paper towels
  • Spray bottle filled with water

Inflatable ball: Exercise balls are recommended but the play ball I purchased for $2.00 from Walmart has endured the creation of three spheres without a problem. Soft beach balls cannot be used because the ball needs to be rigid enough to support the weight of the layers of concrete without sagging. Whichever ball you choose to use, it's imperative the ball stays fully inflated during the whole process. 

Bowls: I use large stainless steel or plastic mixing bowls for easy cleaning. You can usually find plastic bowls and large sturdy plastic spoons for mixing cement at a dollar store, a steal at a $1.00 each!

Gloves: Make sure you have at least 6-8 pairs of disposable gloves available. The fibers in QuikWall may tear the gloves and cement is caustic and not skin friendly! After making several spheres I purchased Nitrile coated gloves and found them superb for working with concrete.

*Tip: There is nothing more frustrating than floppy fingertips on gloves when you're working with concrete. If using disposable gloves, coat your hands with petroleum jelly before slipping on the gloves. This not only prevents the gloves from sliding off your hands but also provides some protection from cement burn if the gloves should tear.

Dust Mask: Because cement is caustic remember to wear a dust mask to protect your lungs and avoid breathing in the fine particles. Once the cement has been mixed with water it is safe to remove the dust mask. 

Vegetable oil spray or petroleum jelly: Vegetable oil spray (PAM) or petroleum jelly (Vaseline) are used as a "release agent". Using either of these agents to coat the ball before applying cement guarantees the ball will easily release from the sphere's interior when it is deflated.

Large pot to support ball: The size of your sphere will dictate which type of pot you choose. I used a sturdy 3 gallon black nursery pot saved from a tree purchase for my larger spheres and clay pots work well for smaller spheres. You'll need to add sand or rocks for weight to prevent the pot from tipping when the ball gets heavier with the weight of concrete. Although it's usually not necessary with a heavier clay pot, I add rocks anyway to guarantee its stability.

QuikWall and FibaTape

 

  • QuikWall Surface Bonding Cement
  • FibaTape for Cement Board

Cement and fiberglass mesh (FibaTape) are the two major components used to create a hollow concrete sphere. The information I've compiled regarding these two components is always the boring part of any presentations I've given. I know you're anxious for the instructions to make a hollow concrete sphere, so I'm not going to include this information in the tutorial. However, I'd like to share what I've learned and will post a "Technical Info" thread for anyone interested in the specific cement and fiberglass mesh I've chosen to create my spheres.

INSTRUCTIONS


Day One:  Gather all materials before starting

  • Cut 6"-8" strips of FibaTape and set them aside.
      (Approximately 20-30 strips should cover a 16" ball) 
FibaTape strips

  • Fill bottom of large pot with rocks or sand for weight
  • Confirm ball is fully inflated and set on pot with inflation tip down.
  • Cover exposed surface with PAM or Vaseline
Fill bottom of pot with stones or sand

  • Determine how large an opening you'd like for the sphere (red dotted line indicates the size of my opening)
  • Apply FibaTape strips to the exposed surface, making sure to overlap each strip
Overlap strips of FibaTape
  • Wearing gloves and dust mask, measure 6-8 cups of QuikWall into the large bowl. Avoid making the most common mistake of adding too much water. Slowly add small amounts of water, mixing after each addition.

When your mix is the consistency of peanut butter you're ready to apply it to the mesh covered ball. If your mix is too wet (soupy), small amounts of QuikWall can be added to achieve the desired consistency.

Cement = consistency of peanut butter
  • Take a handful of the cement mix, make a pattie and use the palm of your hand to apply to the ball surface. For lack of a more sophisticated description, "smoosh" the mix into the FibaTape until it completely penetrates the mesh. Continue this process until the entire surface is covered with a thin layer of cement.

Don't be concerned if the surface isn't "smooth as silk" because you'll be adding two more layers of cement.

  • Loosely cover the entire ball with a large trash bag. Gather the ends of the bag around the base of the sphere and close tightly with tape to eliminate any gaps. Leave for 24 hours
*Tip: If the cement appears to be drying too fast when you're covering the surface of the ball, use the spray bottle of water to lightly spritz the surface as you work. A light spritzing keeps the cement moist for spreading but be cautious ~ too much will cause the cement to slump! To help retain moisture for proper curing and to prevent cracking, lightly spritz again before covering with trash bag after each session.

Day Two:

  • Repeat the process of cutting more strips of FibaTape and mixing cement.
  • Using the small bowl, take 1/3 of the cement mix and add more water to create a soupy mix, i.e. "slurry".
[Slurry is a wetter mix which helps the strips of FibaTape adhere better to the first layer of cement and create a better bond with the second layer.]
  • Remove the trash bag and cover the entire surface with slurry.
  • Repeat the steps for applying the FibaTape strips and another thick coat of the cement mix.
  • Lightly spritz the surface before loosely covering the ball with the trash bag. Secure with tape and leave for 24 hours.

Day Three:

  • Mix more cement, again dividing 1/3 of the mix to add water for slurry.
  • Apply slurry to the surface. (This time it won't be necessary to add another layer of FibaTape.)
  • Add one last coat of the thicker mix and spread over the entire surface. This will be your final layer so strive for a smooth finish before covering. Cover again and leave another 24 hours.

Day Four:

  • Remove trash bag. Rotate sphere to expose opening and place it back on the pot for support. 
  • Carefully cut away and remove any excess FibaTape before deflating the ball.
Remove excess FibaTape

Deflated ball is ready to remove

Slowly deflate the ball. Remove the ball when it is completely free of the interior wall.

 

Once the ball is removed mix more cement to smooth the rough rim of the sphere.

Rough rim

  • Mix small amount of cement and slurry.
  • If you discover tiny cracks on the interior of the sphere use an old paintbrush and 'paint' the cracks with slurry before working on the rim.
  • Work slurry into the rough edges of the rim and then apply cement to form a smooth, rounded edge.
Poultry wire and FibaTape added to rim
  • [Optional] For additional reinforcement bend poultry mesh around the rim and cover with FibaTape before applying the slurry and cement.

FYI: I'm always asked how I achieved a "flat" edge on the rim of my sphere. (Note: this option requires at least one additional day)

  • Pieces of wire (hardware cloth) were cut to form the desired opening. Thin wire was used to connect the pieces and hold them together before applying more cement.
At this point you're almost done!
Hardware cloth added to extend rim
  • Cover with trash bag and secure tightly with tape to form an airtight seal. It's recommended to wait 30 days before painting or staining and sealing to waterproof the sphere. If you're experiencing really hot weather you may want to uncover the sphere daily and spritz with water to prevent the cement from drying too rapidly and then cover again.

*Keep reading to learn how you can finish in just one week!

Sphere is ready for paint!

Painting:

Any exterior latex paint can be used. Patio paints, which are recommended for painting terra cotta pots, are a popular choice because they don't have the tendency to fade in the sun.

Acid stains are another popular choice because they have the ability to create truly unique finishes resembling aged concrete or copper patina. The specific formula used for these stains etches itself into concrete and provides a durable, long lasting finish without fading. However, they're somewhat tricky to use and fairly expensive.

I had hoped to simulate the look of granite with a flat latex paint on the textured surface. The gray base coat failed to meet my expectations, so I added an additional coat of 'faux stone' spray paint in order to achieve the look I wanted.

Sealing:

It is necessary to seal the exterior and interior of the sphere. It's also recommended that you re-apply sealer at least every two years to prolong the life of your sphere.

'Faux Stone' Paint

While any waterproofing sealer (i.e. Polyurethane, Thompson's Water Seal, etc.) may be used they merely form a coat on the sphere and won't provide long lasting protection. It's highly recommended to use a penetrating sealer specifically designated for concrete or masonry. These water-based acrylic sealers are paintable, penetrate the concrete to form a bond with the cement, and actually promote the curing process by retaining moisture.


* Good news! Your sphere can be ready to display in your gardens in just one week! Because penetrating sealers can be applied to fresh concrete you don't have to wait 30 days to paint your sphere. After curing a week the sealer can be applied (preferably two coats) and you're ready to paint!

Most sealers dry within two hours so it's possible to seal your hollow concrete sphere with the recommended two coats quickly and apply your choice of paint all in one day!

Hollow concrete sphere displayed in the garden
Hollow concrete sphere

That's all you'll need to make your own hollow concrete sphere! Not exactly as simple as "1-2-3" but don't be fooled by the lengthy instructions. It's really a piece of cake! Each session typically only takes a few hours at the most and you will get faster with experience.  I was a total "newbie" when I tackled working with concrete for this project and I'm positive you'll be successful as well! All you need is a block of time, a few materials, and in one week you can have your very own hollow concrete sphere to display in the garden. Let your imagination run wild and create your own unique touch with decorative accents or plant your hollow concrete sphere to use as a water garden!

As promised, I'll post an "Info" thread for anyone interested in the technical aspects of the cement and fiberglass mesh chosen for my hollow concrete sphere.

Stay tuned for Part 2 of this tutorial! You'll learn how to make a "closed" sphere with just a few additional steps!

  

 
Comments and discussion:
Thread Title Last Reply Replies
"Technical Info" by rcn48 Aug 24, 2018 6:42 AM 3
Making a sphere by orchidgal Aug 24, 2018 6:33 AM 3
re: Concrete Spheres by EscondidoCal May 15, 2018 1:50 PM 3
Untitled by IrvingLomon Feb 24, 2018 3:13 AM 0
Untitled by laplantemp Feb 3, 2016 9:28 AM 0
Untitled by Allabtdogs Oct 19, 2015 2:55 PM 0
Untitled by bitterswee3 Sep 21, 2015 7:31 PM 0
Untitled by triciacars May 14, 2015 7:53 AM 0
Hollow Concrete by JWaskow Apr 12, 2015 1:30 PM 1
Wonderful! Base instructions? by Charleysmom Mar 9, 2015 12:36 PM 0
Sphere by JudyG Jun 29, 2014 9:53 AM 3
This is perfect! by gg5 Feb 10, 2013 11:01 PM 0
Beautiful! Thank you for this tutorial. :-) by SongofJoy Aug 21, 2011 5:38 AM 7
Neat! by Aguane Aug 19, 2011 1:11 PM 7
Wow!!! Loved it by Ridesredmule Aug 19, 2011 7:24 AM 15
Tutorial Photos by rcn48 Aug 17, 2011 9:24 PM 7
Wonderful tutorial! by plantladylin Aug 17, 2011 2:00 PM 4
Awesome Debra!!!! by Sheila_FW Aug 17, 2011 1:36 AM 1

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