Sources of Recycled Glass

Question:
I want to use recycled glass in my concrete countertops, to make them more “green,” or environmentally friendly. Where can I find it?

Answer:
Crushed glass, also known as “glass cullet,” comes from used bottles and jars, broken windows and windshields, or waste glass produced during the manufacturing process of bottles, windows and mirrors. Generally glass bottles from bars, restaurants and homes get collected and sent off for recycling. Usually little or no processing or screening is done to the glass. The glass is often sorted by color, but not always, and sometimes the bottles are crushed to reduce the bulk volume for storage and shipment.

Glass collected in this way can be very inexpensive, with prices in some areas as low as a few dollars per ton for minimally processed, mixed-colored glass. However, the glass will not be clean, and some paper labels will still be stuck to the glass. In many cities, you can purchase the unwashed cullet either from the city recycling department or from a commercial collection and recycling company. Sometimes the cullet is available for free. Alternatively, you can get used bottles directly from the source: restaurants and bars. Processing the used bottles yourself takes time, energy, water and effort. Cleaning, crushing and screening can be a daunting task if large quantities of glass cullet are required.

Decontaminating recycled glass and crushing it to the right size is very important to making sound concrete countertops. Residual sugars from beverages can cause delayed setting and lowered strengths, and contamination from paper, adhesive and plastic can further degrade the performance and appearance of the concrete. For this reason, it’s vital to thoroughly wash the glass prior to use.

Breaking the glass into small enough pieces is also important. Because concrete countertops are thin, large pieces of glass can weaken the slab. I recommend the largest piece of glass be no larger than about ¾ inch in diameter. Exceptions to this are possible, but larger pieces reduce workability, can lead to internal voids, and can crack or chip if a struck by a heavy object.

Several specialty glass cullet suppliers, terrazzo supply companies and concrete countertop supply companies offer crushed, cleaned and screened glass in a variety of colors, sizes and degrees of processing. Typically glass of a single color that’s different from the typical bottle green or brown starts with remelted plate glass tinted to create new colors. While the original cullet may be recycled, the remelting process consumes energy, making this option less “green” than glass diverted from the waste stream and used more or less as is. However, the advantages are greater design flexibility and greater control of size and color.