Built a small wall section in multiplatta (smooth lightweight concrete), 800(b)*1000(h), which I then continue up to the ceiling with glass blocks as a shower wall. I had PL400 lying around which I used to glue the blocks to the floor and wall, as well as between the blocks. Was it foolishly stingy to use PL400 or is it necessary to use the recommended tile adhesive? They seem to be holding firmly at least.