The following is the process we underwent to make the concrete/glass bench currently installed in the cabin. After a few semi-successful trials, it was time to attempt the full-scale 2’x4’ panels. It was definitely still very much an experiment, but I think we were all very satisfied with the outcome.

Here it is.

1. Collect and crush recycled glass.

I work at an Italian restaurant that does not recycle glass. Instead of tossing away the many wine bottles we go through on a daily basis, I began to collect them. Once we got the okay to explore this as a product in the final design, my collection grew, overpopulating my studio… and the trunk of my car. Time to break them. I first soaked them to remove both the labels and any remaining wine, as the sugar may interfere with the adhesion of the glass to the cement. Then, using just a hammer and a pillowcase, each bottle was crushed until the shards were at a decent size. We later used a small fitted bed sheet over a sheet of scrap plywood which allowed more glass to be broken by multiple people- much more efficient.

2. Experiment.

With small molds, we first experimented with different ratios of glass, cement, concrete, mortar, floor leveler, latex additives, bonding adhesives, etc., etc… Working on a smaller scale allows you to test out the right mixture, without wasting a lot of materials. We found combining glass with just cement, water and a little bit of play sand worked best. When using glass as an aggregate replacement, the gravel and sand in concrete becomes too much.

3. Making the mold.

Carefully measure the desired dimensions. To make our molds, we used scrap pieces of wood lying around the build site. The depth of each panel is 3 inches on the front edge for added strength, 2 inches elsewhere. ½” rebar was cut to size with a hand grinder for reinforcement. Two pieces of ½ ply underneath the thinner area to help with support and to decrease overall weight.

4. The Mix.

The exact amount of each ingredient is hard to say because we used various empty containers around the site as our unit of measurement. Roughly- we used 7 parts glass, 4 parts cement, 2 parts H2O, and a handful of sand. We used a drill attachment for the mixing process. Mixing the concrete wet allows for more working time.

5. Pour.

Fill the mold with the cement/glass mix. Make sure rebar is fully covered and far enough beneath the surface to not interfere with the grinding process. Use a hand trowel to ensure mix is spread evenly. Bull float to smooth surface- we used a 2×4.

6. Vibrate.

Lightly vibrate to consolidate the concrete. We used hammers and lightly tapped the sides. There are more effective and less labor-intensive ways to vibrate the beds, so I would not recommend our method. Do this until air bubbles are no longer on the surface.

7. More Glass.

Next, seed glass on top of the concrete bed and lightly tamp and trowel, avoiding pushing glass too far beneath the surface. This way you can better control the composition of your final surface.

8. Cure Time.

Allow concrete to cure for the appropriate amount of time. We waited 8 days. Cure time varies with size of project.

9. Grinding.

Purchase the necessary equipment. You will need diamond impregnated grinding disks. The grits we used ranged from 50 to 3000, eliminating our need to polish the surface. The disks attach to your stand hand grinder. We had access to some heavy-duty equipment called the StoneMedic, which made shortened the grinding process. It is possible to do it by hand, just make sure your surface is level.

10. Finish.

Depending on the use, there are many different ways to finish the end product. Our bench, we did not finish because the depressions left (from the concrete not being fully consolidated) were not an issue for us. If it were to be a countertop, I would recommend using a concrete sealer if the surface is completely smooth or a heat resistant epoxy/resin to fill in the imperfections and help with sanitation issues.

11. Installation.

DONE! Provide appropriate support and install.

-Pictures on their way…