I have a feature set of x6 195mm glass blocks set in a vertical line within a stud wall. I have ran out of the glass block mortar after doing the first 3. It was left over from a previous project and I know the mortar isn't cheap. More to the point, I only need to set 3 more. My question is, is normal cement ok to use? I know the other stuff grips to glass but if I can manage with cement surely it'll be fine when set?