How Olive Oil Might Save Our Oldest Buildings

When the builders of York Minster—a huge gothic cathedral in a northern U.K. city—set to work, they weren’t thinking about the road traffic that would pass feet from its front door, spilling exhaust fumes onto its magnesian limestone walls. After all, when work began in 1230, even a horse-drawn cart was a luxury few knew.

And they weren’t thinking about the slowly corrosive rain caused by the Industrial Revolution of the 18th century, either. Water, and the acidity in rain (about half of each month the city sees more than 0.1 millimeters of rainfall) can wear on even the best-built buildings. Those charged with building preservation try to keep moisture out of old buildings while allowing them to air from the inside to prevent decay. That’s easier said than done.

Conservationists need to ensure they don’t compromise the building’s look or structure; to do either would be to defeat the point of preservation in the first place. It’s easy enough to drape a waterproof tarpaulin over our oldest buildings, but that hides them from view. Something that keeps the building looking as it did when first built is the end goal of those involved in the preservation of historical sites, and those involved in York Minster’s upkeep have hit upon a novel solution. It’s likely to be found in your kitchen cupboard.

Virgin or extra virgin?

Olive oil drove the Greek and Roman empires. The remnants of ancient amphorae that once held the stuff have surfaced in all four corners of the world, showing the vibrant trade that existed thousands of years ago. Throughout history it’s been a medicine, a sacred liquid and a cooking ingredient—and we produce 3.4 million tonnes (3.75 million tons) of it every year.

Its chemical construction is what makes olive oil so useful for those trying to save buildings from disrepair. The liquid we use to cook with contains between 55 and 83 percent oleic acid, a key ingredient that has the unique quality of being able to let water out from the limestone it covers, while preventing water coming in with a coating a single molecule thick.

Oleic acid is a long chain fatty acid, with a great number of hydrocarbons all lined up in a row—the perfect hydrophobic (water-repellent) chemical construction.

The natural solution

Other solutions had been tried before: The Minster had been coated in other laboratory-made hydrophobic solutions, which stopped the water coming into the stone, but weren’t porous enough to let any pollutants already embedded in the walls come out. Before that, those charged with keeping the Minster healthy had tried linseed oil, though they stopped when they realised they were staining the bright white frontage.

For all it discolored the Minster, linseed oil did work. Which is why Dr. Karen Wilson, a reader in physical chemistry at the University of Cardiff, began experimenting with olive oil-based solutions to the problem of natural decay. By combining oleic acid with a Teflon-like compound called 1H,1H, 2H,2H-perfluoro-decyltrimethoxysilane, Wilson and her team think they’ve managed to find the perfect preservation tool: something that makes the Minster watertight while ensuring its architectural beauty isn’t compromised.

And it’s all because of olive oil.

Wilson’s excited about the solution’s potential. “Such coatings could have a significant impact on stone conservation,” she writes in her academic paper (check it out here), “affording readily applied, conformal barriers able to protect historic limestone from weathering by gas phase and particulate sulfur oxide pollutants.”

The people who built York Minster likely thought their handiwork would be protected by God and stand forevermore. Simple science—and the relentless march of technology—caused it to begin tarnishing. Now the advancement of scientific research might be able to stay the decline in our greatest buildings, using one of the world’s oldest commodities (and cooking ingredients).