I am just writing as I have always laid most natural stone on a full mortar bed with sharp sand 5:1 mix and painted the back of the slabs with a slurry. This is how I was trained to install slabs and also taught this at university with building sand being a big no no.
Recently we have had some issues with builders laying slabs on one of our schemes using the '5 spot' method and clearly causing all sorts of problems.
I have just been on some of the stone suppliers we use (Pavestone, Marshalls, Stonemarket and Bradstone) and all but Bradstone reccommend a 5:1 mix using building sand!! Why on earth are they reccommending building sand to install their pavers, it is way too soft and causes all sorts of structural problems?!
Look forward to hearing anyones thoughts!