Millions being invested to replace bubby concrete at several Hamilton Catholic schools

The Hamilton-Wentworth Catholic District School Board (HWCDSB) will spend almost $22 million removing bubbly concrete at some of its older schools.
The porous material, known as reinforced autoclaved aerated concrete (RAAC), has reportedly weakened over time from water damage, making it crack more easily than alternate materials because of its air bubbles.
As explained in a 2024 white paper commissioned by Infrastructure Ontario by consulting group Rimkus, between the mid-1950s to the mid-1970s RAAC products were commonly used in the construction of buildings in Ontario for wall panels and planks for both roof and floor systems.
“These products have been found to be susceptible to degradation over time, leading to failure, especially when exposed to moisture and adverse structural loading.
“The primary use with RAAC is that it is known to undergo permanent creep deflection over time.”
The Rimkus report defines RAAC as “an accelerated blend of sand, Portland cement and aluminum powder.
“During the curing process the aluminum powder reacts with the lime constituents in the cement along with water creating hydrogen gas. This gas forms air bubbles in the mixture resulting in a lightweight and relatively uniformly porous structure.”
The HWCDSB received provincial funding to remove and replace the RAAC – the same material used in panels at the Ontario Science Centre (OSC) that was abruptly closed in June 2024 due to safety concerns of the roof on the 55-year-old structure that was at risk of collapse.
On the heels of the OSC closing due to RAAC-related risks, the Ministry of Education issued a memorandum in late 2023 requiring all school boards to implement investigation, assessment and management strategies for buildings containing the material.
“The board has received approximately $21.9 million in one-time Ministry (of Education) funding specifically dedicated to the replacement of RAAC through the School Condition Improvement program,” said Debbie McGreal-Dinning, HWCDSB media and communications manager.
The funding will support seven RAAC replacement projects across identified school sites as part of the HWCDSB’s capital renewal plan. All projects utilizing the funds are required to be substantially completed by Aug. 31 pf this year.
McGreal-Dinning said, “The work involves significant building system remediation and the replacement of aging concrete components used in older construction.”
The Ministry of Education has allocated $300 million specifically for the removal and replacement of RAAC at approved school sites. The HWCDSB is one of 18 Ontario school boards across the province receiving funding for these projects. In total, approximately 360 Ontario schools are being monitored for RAAC. That equates to about eight per cent of Ontario’s 4,800 schools.
In the Rimkus report, it’s stated the lifespan of RAAC panels is lower in comparison to other common roof deck types, including steel decks or traditional precast concrete panels.
As a result, roof assemblies constructed with RAAC panels require closer monitoring by facility maintenance staff and more frequent assessments for both the roofing assembly and RAAC panels.
Contractors have not yet been assigned to the HWCDSB projects and according to McGreal-Dinning, “the identified roofs have undergone assessment, and no immediate safety concerns were identified.”
The Hamilton-Wentworth District School Board did not seek provincial funding for RAAC removal as it has reported no replacement of the material is currently required for its buildings.




