CSR’s aluminium operations have tumbled to an annual loss of $29 million because of high energy costs, posing a problem for French giant Saint-Gobain, which is poised to become CSR’s new owner in a $4.3 billion buyout.

CSR has a 25 per cent stake in the Tomago aluminium smelter in NSW, which has been a serious drag on the overall results for the building products company for decades as it battled volatility in aluminium prices and soaring electricity costs.