Harry, I have spoken to the president of Airkrete wall insulation where they use Magnesium Oxide cement. I tried to make a portland based foam concrete as stiff as shaving creme to use as insulation but was unsuccessful. It is always a very runny mixture. I am interested what your results were with the Magnesium Oxide Cement and did you have a mixture that could be used to fill a wall cavity for insulation? Where did you buy the Magnesium Cement and how much did it cost? Thanks Stephen Williams