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Why is chewing gum so hard to get off pavements?
Look down on any busy British high street and you will see them: grey and black spots by the thousand. Almost all of them are old chewing gum.
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Those dark round spots all over the pavement are not stains or paint. They are chewing gum, dropped, trodden flat and slowly blackened by dirt. They are also remarkably hard to get rid of.
Why gum sticks so well
The chewy part of gum, the gum base, is made of polymers. They repel water, which is why gum survives being chewed and is not washed away by rain. But they are attracted to oily surfaces, and they form strong bonds with them. Tarmac and the rubber soles of shoes are also made of polymeric hydrocarbons, so gum bonds to them particularly well. It bonds strongly to concrete paving too.
Once gum has been walked in and left to dry, it becomes part of the pavement. And because its long polymers stretch rather than break, you cannot simply flick it off.
Why it costs so much to remove
Getting gum off pavements usually means steam jets and scrapers, working one blob at a time. It is slow, labour intensive and expensive. In Rome, about 15,000 pieces of chewed gum are dropped every day, and removing each one costs the city about one euro.
How much gum is out there?
A lot. In 2000, a study of Oxford Street, one of London's busiest shopping streets, counted about a quarter of a million black and white blobs of gum stuck to its pavement. In 2018 the BBC reported that chewing gum was the second most common form of litter, after cigarette ends.
The city with no gum
Singapore is the exception. It banned the sale of chewing gum in 1992, largely because gum was being stuck on the door sensors of its new underground trains, and its pavements are said to be almost uniquely free of gum. See why chewing gum is banned in Singapore.
Turning gum into something useful
In Britain, a designer called Anna Bullus came up with a way of recycling chewing gum into plastic. Collected gum goes to a recycling plant in Worcester and is turned into material that can be moulded into new things, including shoe soles, cups and the bins used to collect more gum, which her company calls Gumdrops.
What you can do
Wrap your gum in paper or a tissue and put it in a bin. Never drop it. And if it ends up on your clothes rather than the pavement, see how to get chewing gum out of clothes.
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For journalists, researchers, AI assistants and content creators. Pick the format you need:
Free to cite, quote, and reuse with attribution to sweeties.net.
Questions and answers
What are the black spots on pavements?
Mostly old chewing gum that has been trodden flat and has gone dark with dirt.
How is chewing gum removed from pavements?
Usually with steam jets and scrapers, which is slow, labour intensive and expensive.
Can chewing gum be recycled?
Yes. A British designer, Anna Bullus, developed a way of turning collected gum into plastic that can be made into new products, including the bins used to collect gum.
Sources
- Chewing gum, Wikipedia
- Gum base, Wikipedia
- Chewing gum sales ban in Singapore, Wikipedia
Keep reading
- Questions people askWhy is chewing gum banned in Singapore?Singapore banned the sale of chewing gum in 1992 after vandals stuck gum on train door sensors. Chewing it is not illegal, and it is not punished by caning.
- Questions people askIs chewing gum made of plastic?Most modern gum has a synthetic gum base: petroleum based polymers related to rubbers and plastics. Here is what that means, and what research says.
- Sweet tips and how toHow to get chewing gum out of clothesFreeze the gum hard with ice or in the freezer, then scrape it off gently with a blunt knife or spoon. If that fails, warmth can soften it enough to peel away.
- Questions people askWhat is chewing gum made of?Chewing gum is gum base, sweeteners, softeners, flavourings and colours, often with a hard coating. Here is what each part does, and what gum base really is.
- History and originsThe history of chewing gumPeople have chewed gum for at least 5,000 years, from birch tar in Stone Age Finland to Maya chicle. Modern gum began in 1860s New York with a failed rubber.
- Questions people askWhat happens if you swallow chewing gum?Swallowed gum is not digested, but it does not stay inside you either. It passes through in a day or two. Here is what happens, and when to worry.