“Bubbly” concrete, pioneered in Sweden, swept Europe through the middle of the last century. Known as “aerobar”, “aircrete” and Raac (reinforced autoclaved aerated concrete), the cheap lightweight alternative to traditional concrete mixes was used in thousands of UK public buildings from the 1950s to 1990s. By the 1980s it had started to fail and buildings had to be demolished. This is a timeline of who knew what and when. 1980s – With an estimated 30-year lifespan, failures among Raac roof panels in 1950s buildings were inevitable. Engineers also discovered some panels were too thin for the distance they were used to span, some lacked enough steel to anchor them to vertical structures, and leaky roofs triggered a “rapid worsening” of steel corrosion. 1996 – The UK’s Building Research Establishment (BRE), an executive agency of the government, issued an “information paper” about Raac concrete roof planks installed before 1980 that warned of “excessive deflections and cracking”. There was no evidence “so far” to suggest they posed a safety hazard to building users, but it said Raac could not be expected to have a useful life of much more than 30 years. A proposal was made to remove the reference to Raac from the British Standard for structural concrete as it gave it “an unjustified respectability” and “the impression that it can be used for permanent structures”. 1999 – The Standing Committee on Structural Safety (SCOSS), chaired at the time by the distinguished chemist Jack Lewis, a crossbench peer, urged those responsible for schools with pre-1980 Raac-plank roofs to arrange inspections. The level or threat appeared to be low and a report by the engineering profession body said that “generally, the deterioration of Raac planks does not jeopardise structural safety”. It also warned: “Complacency can preclude recognition of increasing risks.” 2002 – The BRE, now privatised but still working closely with the government, issued a review of Raac’s “rather mixed” behaviour which highlighted “excessive in-service deflections and cracking” in pre-1980 buildings. July 2018 – A period of calm about the risk from Raac ended when the ceiling of the staff room at Singlewell primary school in Gravesend, Kent, collapsed on a Saturday evening having shown signs of structural stress the previous day. No one was hurt but the images of the destroyed room suggested people could have died. The school had been rebuilt in 1979 using Raac after a fire. December 2018 – The Department for Education (DfE), then led by Damian Hinds MP, joined forces with the Local Government Association to contact all school building owners in England about the Kent collapse. They advised them to “check as a matter of urgency” for roofs, floors, cladding or walls made of Raac. Schools were told two recent failures meant the working assumption that Raac planks gave adequate warning of failure through visual deterioration “can no longer be relied upon”. 2019 – The Ministry of Defence (MoD) issued its own alert to UK estates staff highlighting the school collapse, which was preceded by “little to no warning”. It also highlighted a partial shop collapse. May 2019 – SCOSS issued an alert for government departments, councils, NHS leaders and building professionals highlighting the “significant risk” of failure of Raac. “Sight must not be lost of the fact that the 2018 collapse was sudden with very little noticeable warning,” it said. An Institution of Structural Engineers (IStructE) study group was tasked with investigating. April 2020 – SCOSS published findings from surveys of buildings that revealed Raac beams suffered noticeably from water ingress, cracking, spalling and surface corrosion. The expert who assessed the buildings said they “require rectification” but there was not “an enhanced risk of sudden shear failure”. February 2021 – The DfE published a Raac guide for the education sector in England. In the same year the Cabinet Office’s property team issued a formal warning notice stressing Raac was “now life-expired and liable to collapse”. March 2022 – Raac problems aside, demand for money to rebuild crumbling schools in England far outstripped available funds. This month, 1,105 projects were nominated for funding but only 61 were successful. In 2021-22 capital spending by the DfE was about £4.9bn, the lowest recorded since 2009-10. IStructE said 1960s and 1970s Raac was showing “structural deficiencies”, citing “sudden failure of panels”. Amid mounting concern, the DfE issued a questionnaire asking schools, councils and academy trusts about Raac in their buildings. September 2022 – the Cabinet Office’s property arm told all Whitehall property leaders: “Raac is now life-expired and liable to collapse.” October 2022 – The education minister Lady Barran chased councils in England for responses to the March questionnaire saying it was “of the greatest importance” and that buildings with Raac must be monitored “to ensure they remain safe”. December 2022 – The DfE’s annual report clearly warned: “There is a risk of collapse of one or more blocks in some schools.” March 2023 – The MoD gave military officials until the end of July to check buildings for Raac in the UK defence estate, with fixes to be carried out by December. Loughborough University, which had been earlier commissioned to investigate Raac for NHS England, said seven health trusts had buildings predominately constructed of RAAC. May 2023 – The DfE identified that Raac might be present in 572 schools in England, but at this point more than 8,000 schools had not been checked. August 2023 – The Health and Safety Executive announced: “Raac is now life-expired. It is liable to collapse with little or no notice.”