How to create a large-scale mosaic sculpture using EPS foam (expanded polystyrene) and Quikrete

How to create a large-scale mosaic sculpture using EPS foam (expanded polystyrene) and Quikrete

Before starting this tutorial, I would love to give a huge “thank you” to the Salt Lake City Arts Council for providing an Arts Learning Grant so I could create this project, and to Quikrete for graciously donating the Repair mortar and Fast-setting concrete mix used in the construction of the form. Thanks also to Artists for Local Agriculture and its partner organization the Utah Arts Alliance for hosting this sculpture in the Utah Arts Alliance Community Art Garden.

Materials needed for form:
– Large blocks of EPS foam *
– Foam adhesive
– PVC Pipe / connectors / adhesives
– Rebar
– Self adhesive fiberglass mesh tape for concrete (Fibatape works great)
– Metal Lath
– Quikrete Fast-Setting Repair Mortar
– Quikrete FastSet Concrete Mix
– Large cardboard tube for concrete
– Acid stain *
* Available in specialty stores or online. ACH Foam is my local supplier of large EPS blocks. Alta Paints is my local supplier of concrete stains.

Tools needed to create form:
– Handsaw
– Sandpaper
– Particle mask
– Tin snips
– Wire cutters

Materials needed for mosaic:
– Tiles (Porcelain and/or glass) – be sure that your ceramic tiles are high-fired so they can withstand the elements. When in doubt, ask!
– Thinset mortar
– Grout
– Grout sealer

Tools needed for mosaic:
– Compound tile nippers (regular tile nippers work as well, but require much more effort for basically the same result)
– Hammer (another basic tool for breakting the tiles)
– Safety glasses
– 1/4″ notch trowel
– Drill
– Concrete mixing bit
– Tarp
– Grout float
– Grout sponges
– Buckets
– Vinyl gloves

Step 1: Design
Having a plan can make a big difference. As you can see from the sketch below, as compared to the final results, major changes to the original plan were made based on practicality and weight of the finished form. That said, the sketch still served as a vital starting point to determine how the sculpture would come together.

Step 2: Form shape
Deconstruct your design into its simplest parts, and determine how many pieces will have to come together to make your sculpture. Preferably it should all come from the same block of EPS; based on my design, however, I determined that three separate shapes would generate far less waste.
The EPS foam blocks were not quite large enough to create the forms I wanted, so I started by using foam adhesive and gluing blocks together.
Next, I used the handsaw to carve off large pieces of the form, and then smaller pieces until I had thee separate forms (head, torso, tail) that looked like the ones in my sketch.
Finally I used sandpaper to smooth out the form.
Note: Cutting and sanding EPS is very messy and creates a lot of dust. This can be avoided by using expensive hot-wire tools, or it can be embraced by wearing a particle mask and simply getting messy (as I did on this project). Be sure to do the cutting and sanding on a floor that can be swept. If a vacuum needs to be used at any point for the EPS debris, use a shop vac, as the particles of EPS can easily clog a normal vacuum.

Step 3: Inner structure
The inner structure of your form serves two purposes:
1. Keeps the pieces of the sculpture together.
2. Provides strength to the form to protect it from damage
Knowing that this sculpture was going in a public garden, and guessing that despite common sense someone would likely climb on it, I chose to use a combination of PVC pipe and rebar as the skeleton to hold the form together.
Because the skeleton ran through the middle of the form I needed to saw the form in half and create crossbars in order to hold the two halves of each section together.

Step 3: Outer structure
Once the form has been created, with an inner structure, it is ready to wrap. First, use self adhesive fiberglass mesh to mummify the sculpture. This will allow for the rapid set mortar to hold tightly to the EPS.
Depending upon the size and use of the sculpture, fiberglass mesh may be sufficient. To prevent possible abuse in a public setting, I decided to use metal lath as an additional layer of protection to the sculpture. I cut pieces of metal lath and used thin wire to tie it together around the sculpture. Since this project I have changed my technique a bit, and I usually either use garden wire stakes or simply bend “U” shapes out of thicker wire and push them down to hold the metal lath flush with the sculpture.
Next I used a concrete mixing attachment on my drill to mix the fast-setting repair mortar to a peanut butter consistency. I rested the sculpture on a large tarp and applied the mortar using a trowel and my hands (wearing vinyl gloves). I set mortar to about a third of the sculpture at a time, and gave that section sufficient time to set before turning, so gravity would be on my side.

Step 4: Mosaic
One the rapid set mortar has a few days to set, I took the sculpture to the Downtown Arts and Crafts Market in Salt Lake City to recruit a small army of random kids to help assemble the tiles onto the sculpture.
Hats off to Mark Brody and his team of helpers at the community project of the Society of American Mosaic Artists 2013 summit who taught me the following trick for direct method application in a community mosaic setting (adapted to my sensibilities):
1. Use a large plastic cooking spoon to scoop out dry mortar
2. Use a trowel or a gloved hand to mix the mortar to a creamy peanut butter consistency in a small bucket
3. Scoop the mortar out of the bucket into a Ziploc bag
4. Use a cable tie to seal off the zipper-half of the bag.
5. Cut a hole in the bottom of the bag large enough for mortar to escape
6. Voila! You have a mortar “frosting” bag!
One of the main advantages of the mortar-frosting-bag method is that the mortar stay moist and active much longer, and thus gives more time in between mortar-mixing sessions.
Before each child began helping, I went over a quick safety lesson and had them put on vinyl gloves (which were open far too large). I usually began by using the frosting bag to create lines of mortar on which they were to assemble tiles. Once they appeared to have a knack for it, I could then feel confident handing them a mortar bag so they could work more independently.

Step 5: Mounting the sculpture
Once I has the tiled sculpture at a level of completion I was comforable with, I transported it to the community garden. I dug a hole two feet deep so the sculpture would be anchored into the ground and placed a large cardboard tube for concrete in the hole.
Then I somehow balanced the bee, then weighing hundreds of pounds, on its tail and directed the rebar attachment into the cardboard tube. I used wood to balance the sculpture at the angle at which I wanted it. I then mixed fast-set concrete to a sloshy consistency and poured it into the carboard tube until it was overflowing.

Step 6: Finishing the sculpture
Now that the sculpture was mounted, I finished tiling the form, attached the wings (which were completed separately), waited 24 hours, and then grouted between the tiles.
Using fast-setting repair mortar and metal lath I created a transition form from teh body to the wings. I also used additional repair mortar to add drip lines to the post to give it more of a natural, organic feel. Once that had set I used acid stain to give it an earthy reddish-brown tone.
Finally I used grout sealer and a rag to polish off the finished product, added the decorative landscape around it, and celebrated its completion at a community party (which also celebrated the opening of the garden).

Concrete sculpture is definitely no piece of cake, but it’s a very physical and real art process, working against dry times, gravity, and other basic laws of physics. In other words it’s a lot of fun :)

Thanks for reading!