Ask the Expert
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In this regular column, Consultant Barry Hunt answers reader enquiries. If you have a question, email it to: nss@qmj.co.uk marked for Barry’s attention
Q: What is the best way to get rid of chewing gum from stone surfaces?
Every public space seems to be blighted by chewing gum. In a recent Lords debate on the problem, Lord Selsdon referred to it as “gum turd”, it being an excrement that is potentially full of respiratory pathogens, blood, viruses and bacteria.
A fortune is spent on dealing with this litter as it is so difficult to remove, which, it might be argued, gives good grounds to tackle the problem head on at source and ban the stuff altogether. The latest figures from the Department for Environment Food and Rural Affairs state that some authorities spend as much as £200,000 a year dealing with the problem and that about £5million is spent across the UK.
When chewing gum is relatively fresh it sticks to everything and makes large scale removal difficult as it clogs the implements trying to scrape or scrub it away. When it is older it goes harder and while it becomes brittle to some degree, also becomes more difficult to remove. Where stone is concerned, chewing gum tends to be pressed into the stone’s surface texture by foot traffic, making it even harder to remove completely .
There are no chemicals that could be used easily and safely to remove chewing gum, and even if there were, the costs of using them would be prohibitive. Freezing gum to make it brittle for easy removal is a well known process but is not practical in large streetscapes where, again, the time and cost would be prohibitive.
By far the most effective process I have seen used is high pressure, hot water jet-washing, using water heated to between 80°C and 90°C. The hot water softens the gum while the force of the water peels it from the stone surface. And as the released gum and surrounding area is wet, the gum is unable to stick back down and is simply vacuumed up. This process has proven effective in several towns, including Stratford-on-Avon where hordes of gum-chewing tourists create an immense problem.
The process cannot be used where the construction is unbound as jointing will be rapidly washed away – a good reason for favouring the use of bound construction in public areas.
The force of the water-jet needs to be controlled. In one particular instance, inappropriate water-jetting actually excavated sandstone paving up to 25mm below the gum it was removing.
To avoid this, trials to determine the maximum pressure are essential and a 10-20% safety factor should be included before damage can occur.
The removal of chewing gum is thus a specialist operation for a competent contractor and cannot be undertaken easily in any other way at the present time. If the problem is small, you could try one of the chemical treatments that are available, though most of these are for use on fabrics.
Finally, let’s hope that the recent Clean Neighbourhoods and Environment Act 2005, which enables fixed penalty notices to be issued to gum-dropping individuals, will be taken up and enforced by all local authorities. I fully support local authorities such as Leicester City Council, who were prepared to fine those who chose to discard gum in an inappropriate fashion well before the legislation came into being.
Reference
Hansard. House of Lords Debates, Tuesday 31 October 2006.
Barry Hunt is a Chartered Geologist and Chartered Surveyor who has spent 20 years investigating issues relating to natural stone and other construction materials. He now runs IBIS, an independent geomaterials consultancy undertaking commissions worldwide to provide consultancy, inspection and testing advice. Tel: 020 8518 8646
The advice offered in answer to readers’ questions is intended to provide helpful insights but should not be regarded as complete or definitive. Professional advice should always be sought with all stone-related issues as each problem will inevitably have its own unique set of circumstances.
Q: What is the best way to get rid of chewing gum from stone surfaces?
Every public space seems to be blighted by chewing gum. In a recent Lords debate on the problem, Lord Selsdon referred to it as “gum turd”, it being an excrement that is potentially full of respiratory pathogens, blood, viruses and bacteria.
A fortune is spent on dealing with this litter as it is so difficult to remove, which, it might be argued, gives good grounds to tackle the problem head on at source and ban the stuff altogether. The latest figures from the Department for Environment Food and Rural Affairs state that some authorities spend as much as £200,000 a year dealing with the problem and that about £5million is spent across the UK.
When chewing gum is relatively fresh it sticks to everything and makes large scale removal difficult as it clogs the implements trying to scrape or scrub it away. When it is older it goes harder and while it becomes brittle to some degree, also becomes more difficult to remove. Where stone is concerned, chewing gum tends to be pressed into the stone’s surface texture by foot traffic, making it even harder to remove completely .
There are no chemicals that could be used easily and safely to remove chewing gum, and even if there were, the costs of using them would be prohibitive. Freezing gum to make it brittle for easy removal is a well known process but is not practical in large streetscapes where, again, the time and cost would be prohibitive.
By far the most effective process I have seen used is high pressure, hot water jet-washing, using water heated to between 80°C and 90°C. The hot water softens the gum while the force of the water peels it from the stone surface. And as the released gum and surrounding area is wet, the gum is unable to stick back down and is simply vacuumed up. This process has proven effective in several towns, including Stratford-on-Avon where hordes of gum-chewing tourists create an immense problem.
The process cannot be used where the construction is unbound as jointing will be rapidly washed away – a good reason for favouring the use of bound construction in public areas.
The force of the water-jet needs to be controlled. In one particular instance, inappropriate water-jetting actually excavated sandstone paving up to 25mm below the gum it was removing.
To avoid this, trials to determine the maximum pressure are essential and a 10-20% safety factor should be included before damage can occur.
The removal of chewing gum is thus a specialist operation for a competent contractor and cannot be undertaken easily in any other way at the present time. If the problem is small, you could try one of the chemical treatments that are available, though most of these are for use on fabrics.
Finally, let’s hope that the recent Clean Neighbourhoods and Environment Act 2005, which enables fixed penalty notices to be issued to gum-dropping individuals, will be taken up and enforced by all local authorities. I fully support local authorities such as Leicester City Council, who were prepared to fine those who chose to discard gum in an inappropriate fashion well before the legislation came into being.
Reference
Hansard. House of Lords Debates, Tuesday 31 October 2006.
Barry Hunt is a Chartered Geologist and Chartered Surveyor who has spent 20 years investigating issues relating to natural stone and other construction materials. He now runs IBIS, an independent geomaterials consultancy undertaking commissions worldwide to provide consultancy, inspection and testing advice. Tel: 020 8518 8646
The advice offered in answer to readers’ questions is intended to provide helpful insights but should not be regarded as complete or definitive. Professional advice should always be sought with all stone-related issues as each problem will inevitably have its own unique set of circumstances.