The UK’s two biggest airports have discovered the type of concrete that led to recent school closures, piling pressure on Prime Minister Rishi Sunak as he grapples with fading public faith in the Conservative government.

Heathrow and Gatwick, which together handle almost 100 million passengers a year, said they are aware of the use of Reinforced Autoclaved Aerated Concrete, known as Raac, the Times reported. The porous material, used between the 1950s and mid-1990s, is prone to corrosion as it ages.

It comes amid separate revelations from the Financial Times that the UK government ignored independent advice in 2020 to identify buildings that contain the potentially dangerous lightweight concrete that’s recently been found in more than 100 schools.

The presence of the Raac at the airports adds to a growing list of aging public buildings and infrastructure in need of maintenance following years of underspending. It’s another headache for Sunak, whose Conservative Party trails Labour by some 20 points in recent polls ahead of a general election that’s widely expected in 2024.

Various government departments are trying to assess how prevalent the lightweight concrete is across UK buildings. Sunak has faced accusations that he personally approved cuts to capital spending on school buildings when he was Chancellor of the Exchequer, despite warnings of the risk posed to pupils and teachers.

Read more: UK Sets Aside £700 Million to Fix Crumbly Concrete in Hospitals

Heathrow has known about the presence of Raac in Terminal 3 since last year and has already put measures in place to mitigate any risk, the Times said. It’s not thought that the concrete at either airport will cause the same level of disruption as it has in schools, it said.