Bought some glass blocks from Wickes to fill an opening near the ceiling. Given than the height of the opening is 410mm, each block is 190mm I had hoped to fill the opening 2 blocks high. Problem is getting spacers in. Theoretically it should be possible with a 10mm spacer between and 10mm on the base and ceiling but it seems impossible in practice. Any one experience of this sort of thing? Or any one any advice?