Traditional Masonry Archives

Removing Graffiti from Stonehenge
Removing graffiti from any from Stonehenge is not just scary to contemplate,
it's positively nerve-wracking.

Removing graffiti from any historic stone structure is scary to contemplate. Removing it from Stonehenge, one of the oldest stone monuments on the planet, must be positively nerve-wracking. Screw it up, and the whole world knows.

Luckily, England boasts a few hardy souls who have proven equal to the task.

Bob Bennett, MBE, sole proprietor of The Lime Centre, and his co-worker Juliet Stevenson were called into service in the early 1980s when vandals hit the famed structure with oil-based paint, daubing the phrase "Save The Ponies" onto the monument with one large letter per stone. "During a very cold winter the wild ponies that inhabit the forest start to starve and some die," explains Bennett, 73. "Young girls and some animal supporters want to make the situation as public as they can."

Bob Bennett used delicate aluminum oxide crystals and lumps of a homemade dung mixture to restore Stonehenge to its traditional glory after the monument was defaced with paint in the early 1980s.

Once the press got hold of the story, contractors from across England offered to clean the stone free of charge. But English Heritage (officially known as the Historic Buildings and Monuments Commission for England), which helps the British government manage the site, asked Bennett and Stevenson to help instead. "She was already renowned for her expertise in cleaning a variety of masonry," Bennett says. "I'm one of the first people in the country to get involved with caring for historic buildings."

The pair's first priority was to not damage the stones further. The big rough-hewn stones are hard granite that originated in Wales. To clean them, the pair rejected all graffiti removal chemicals, settling instead on a pen-sized gun that would fire aluminum oxide crystals at very low pressure.

As Bennett himself admits, most any kind of abrasive will damage the masonry underneath the offending marks. But aluminum oxide crystals are as fine as talcum powder. They are so gentle that you can use them to clean your own skin, Bennett says.

Even so, would scouring with crystals, no matter how small, really be able to remove paint from the ancient surface without damaging the surface itself? You'd better believe it. "With multicoated paint I can remove each layer by one micron at a time with this method," Bennett says.

He demonstrates the sensitivity of the instrument with a chicken egg. "Using the pen-sized gun I cut a small hole at the top and bottom. The yoke and albumen is blown out, leaving the fine membrane clinging to the inner wall of the egg. Using the same pen-sized gun I cut doors in the side of the egg. On three sides I also cut through the membrane, but on the fourth side I cut the shell but stop when I get to the membrane. I now have a door on the side of a chicken's egg that will open and close on the membrane hinge."

The pen gun worked, and the paint was successfully scoured off the stones. But the rescuers were immediately confronted with another problem. The stones are covered with centuries of lichen and moss, and most of the paint had soaked into the growth, with very little making contact with the granite. When the pair removed the paint, they removed the growth, creating a ghosting effect. "After having removed the graffiti without marking the stones, the offending message could now be seen as clean stone," Bennett says.

At this point, Bennett and Stevenson got their hands dirty — literally. To promote quick regrowth of the lichen and moss, they had to apply some sort of fertilizer to the faces of the stones. They worked up a solution of cow, chicken and pig dung mixed into sour milk. Bennett cheerfully calls it a "s--- cocktail."

"I tried applying it gently with a brush, but Juliet was far more effective just throwing handfuls of the mix in an apparently random way," Bennett says. "The clever thing was that there was not a visually obtrusive pattern to her work, whereas mine looked too formal."

The pair startled a couple of tourists, Bennett remembers, who were not immediately clear as to why the rescuers were hurling excrement at the internationally beloved landmark. But the nasty stuff did the job. "Within about three or four months the stones were back to their former appearance, complete with algae," says Bennett.

In general, Bennett says, The Lime Centre follows a simple regime when commissioned to deal with graffiti.

First, he says, stand back from the job and take a long look at what has happened. "People rush in and do silly things. Time spent quietly looking at it can make a difference. Just one stupid act can ruin it."

Then determine the nature of the background onto which the graffiti has been applied. Is it stone, brick, render, plaster or a form of plastic? Pay particular attention to the surface's tendency to absorb water.

Take a very small sample of the offending material and define its chemical structure. Is it oil paint? Emulsion paint? Aerosol material pencil?

Having determined the chemical structure of the offending material, identify the solvent or product that will render the material water soluble and easy to remove. On a typical graffiti removal job, a substance like sodium hydroxide will do the trick.

If the surface is too porous, large pores will absorb the loose, saturated paint into the masonry. In these cases, Bennett soaks the stone surface with water before applying the paint loosener. A poultice of attapulgus clay will draw the contaminated water out of the pores.

Porosity wasn't a factor with the granite of Stonehenge, Bennett notes. "The stones are very hard, not very absorbent. They have a fine capillary."

It was another complication, weather, that drove Bennett and Stevenson away from paint looseners. "Had we used a solvent during the severe winter and tried to wash the dispersed material away, we would have got into serious problems with water freezing within the first millimeter or so of the stones," he says. "When water freezes, it expands by up to 9 percent, and the surface of the stones could have been damaged."

Finally, he says, only work with people who have been trained and know what they are doing. "NEVER go for the cheapest quotation."

TM