Dear Glass Detective,
I am tired of seeing glass bottles and jars not getting recycled. I am wondering two things—first, is there an R-value for broken glass, such as gabion glass or broken bottles? Secondly, I want to build a fence made of broken or whole glass bottles and would like to know if you have any suggestions.
Thank you for making contact with the Glass.com Glass Detective regarding your concerns about glass recycling. Your comments were that you are tired of seeing glass bottles and jars not getting recycled and you were wondering if they perhaps could be used for fencing or maybe even other types of structures. You further asked about possible “R-Values” for broken glass or broken bottles. While this is a bit of an unusual question for us, it is a relevant topic in today’s society where reusing and recycling is very important. While our experience is a bit limited in this area, we have some knowledge. So with the understanding that a little knowledge on any given subject can be a bit dangerous, here we go:
Glass recycling is very difficult for a number of reasons. While glass manufacturers like to mix in broken glass with the raw product mix at the time glass is made, they only want to recycle “clean glass.” This clean glass, called cullet by glass industry people, is typically broken glass that came from a previous batch of manufactured glass—either trim pieces or over-runs. It is only used because it helps raw materials melt and form more readily. For the most part, the manufacturers would hardly ever consider using any outside (recycled) glass for new architectural glass manufacturing.
A few years back, I was running a large reglazing project at the University of Chicago and one of the job requirements was that we recycle at least 30% of all the materials removed from the jobsite. Most of the removed product from the job was very large pieces of clear plate/float glass. After a great deal of effort, I was able to find a company in Michigan that would take the old glass but only on the condition that all of the edges (which would have some caulk residue on them) be trimmed off first. Then these large pieces of glass had to be cut down to a size that would fit into the recycling containers that were sent to the job site. Last but not least, these recyclers would not pay for any of the old glass. Because we could not find anyone else that would even talk to us about this project (from a glass recycling perspective) we complied with the requirements and learned a lesson from all of this. And where, you might ask, did our used glass go? It went to a company in Michigan that manufactured highway paint. They ground the glass up and mixed it in with that yellow highway paint that is used throughout the country. There’s a good chance that I have driven next to or maybe even over that very glass during these past few years.
Bottle manufacturers are a better choice for glass recycling because most bottles are tinted and the glass does not have to be as perfect as for other products. But even here, glass that is going to be recycled typically cannot be coated. Most architectural glass has a coating of some type (usually low-e coatings) and most of the time cannot be reprocessed. On a more encouraging note, there is some progress being made with recycling windshields and we are actually in the process of trying to get a better handle on what the future might hold in this arena. Windshield recycling poses particular issues because windshields are made from laminated glass. Laminated glass is basically a glass sandwich of two layers of glass with a polyvinyl layer in the middle. In order to recycle the glass, the polycarbonate interlayer must be separated.
Lastly, you asked if perhaps old glass bottles could be used in construction projects. You specifically mentioned fencing. You wanted to know what the R-value might be for such bottles. The R-value refers to the level of thermal resistance a product has. How well it insulates. If a bottle were sealed (not open at any point) it would have some thermal resistance because we know that dead air, or air that is not circulating, has some value for insulation purposes. I would guess that if you found out what the R-Value of a glass block is, you could compare that to a glass bottle or jar for the sake of having some type of an R-Value estimate. Glass block is typically set with a mortar mix so why not set glass bottles and/or jars the same way? You’ll probably need some structural support of some kind to make sure the thing doesn’t fall over but conceptually, it could work.
Your question is truly of interest to a lot of people because there is no doubt whatsoever that tons upon tons of used and broken glass is being dumped into landfills around the country every year. I called a friend of mine who is in the waste hauling business and asked him what percentage of glass put out by consumers trying to be resourceful actually gets re-used. He made me promise not to use his name or his company’s name if he provided an answer. I promised him that he would forever remain anonymous. Given that assurance, he told me that he sincerely doubts if as much as 15% of all glass put out by consumers is ever actually recycled. His prediction is based on the assumption that it is often far cheaper to use new raw materials (in most applications) than to deal with recycled glass products. I’m not sure how accurate that assessment might be, but having seen what I have seen, I think there is a good chance that his estimate is correct. We have a long way to go here.
Thank you again for contacting the Glass.com Glass Detective and I truly hope this information is of some value to you.