Hot bitumen (or asphalt) is still the advised solution to install cellular glass on a roof. A movie of GLAPOR shows how the plates are almost submersed in the viscous liquid. The result is a vapour tight thermal insulation, avoiding any internal condensation and resisting large wind loads. For cellular glass roofs, typically bitumen 85/25 is used, which is an oxidized bitumen. These bitumens have superior characteristics, which are important for a flat roof. Most bitumen originates from crude oil and can be considered as waste during the production of gasoline, diesel, … .But it has also important disadvantages:

• In order to liquefy, we have to heat it above 180°C, which induces always a fire risk on the job site.
• To heat it up, we need a heating equipment on the roof, which needs always attention.
• The hot liquid can of course induce severe injuries on the skin when hot.

But there are also serious heath risks. Oxidized bitumen is by the IARC, part of the World Health Organization , classified as “probably carcinogenic to humans” (Group 2A). The other bitumens, namely the ones for mastic work and road paving have a lower classification: “possibly carcinogenic to humans” (Group 2B).

It is now the target to find an alternative, which is liquid without heating during installation of the cellular glass boards and hardens very fast to allow the installation of the next layer. On top of that, it has to be cheap like bitumen. Personally, I doubt that the joints can have a lot of internal condensation and for that reason, I suggest to consider a ceramic alternative based on natural hydraulic lime.