For Antoni Gaudí, completing the Sagrada Família was always a matter of time, not imagination. He knew precisely what the six central towers should look like. What he could not have foreseen was that, more than a century after his death, an industrial adhesive would prove essential to realising his vision.
The towers have now been finished, just ahead of the centenary of Gaudí's death. But behind this architectural milestone lies an unexpected protagonist: Loctite EA 9497, a product from the German chemical company Henkel. This adhesive has made it possible for stone and steel to behave as a single material, solving structural challenges that would have baffled Gaudí's contemporaries.
Engineering a Cathedral with Glue
The scale of the task was immense. The towers were built using a modular system of prestressed stone panels — 826 in total — incorporating more than 2,100 stone elements bonded to metal structures. Each panel required around 30 kilograms of adhesive. In all, 24 tonnes were applied in liquid form, filling every cavity and securing the joint before a curing process of roughly 24 hours.
The result is not only aesthetic but structural. The bond can withstand loads equivalent to 100,000 people per square metre — the full capacity of a stadium like Camp Nou, or the weight of 1,600 African elephants. This explains how the Tower of Jesus Christ, the tallest of the ensemble, can support the large cross that crowns it without compromising a single millimetre of stability.
The environment adds further complexity. The basilica stands just over two kilometres from the Mediterranean, exposed to constant salinity and a permanent risk of corrosion. Underground, two metro lines transmit constant vibrations through the structure. The adhesive had to resist all of this.
The collaboration between Henkel and the Sagrada Família has been ongoing for more than a decade, with testing that goes beyond usual standards and a logistical supply chain adapted to a rare funding model: the project is financed solely by visitors' contributions, with no fixed timetable or closed budget.
The upshot is already part of history. At 172.5 metres, the Sagrada Família is now the tallest religious building in the world, surpassing Ulm Minster in Germany. Pope Leo XIV recently blessed the Tower of Jesus Christ, its central spire, marking a spiritual milestone for the basilica.
"This project shows how innovation and collaboration continue to drive progress," says Adrián Orbea, president of Henkel Ibérica. It is a sentiment that Gaudí himself might have endorsed, had he lived to see his masterpiece completed.
The completion of the central towers also offers a rare glimpse into Gaudí's hidden symbols. A recent tour of the basilica revealed intricate details that had remained concealed for decades, adding layers of meaning to the already rich iconography.
For Barcelona, the Sagrada Família remains a living monument — not just to faith, but to the marriage of tradition and technology. And for Europe, it stands as a testament to what can be achieved when imagination meets engineering.
