Hello people. I am intending to lay a natural stone slab in my patio. At the moment there is a horrible 2" thick grey slab with concrete patches in between (ex-council). Can i lay over the top of this and do i have to use sharp/concreting sand for the mortar bed? Is it possible to use building sand as i have this in abundance? The new slabs are natural stone and vary in thickness between 18mm - 35mm. I have about seven inches at the highest point to my damp course. Any help would be mightily appreciated!!! javascript:emoticon('')