The books stress having the slab flat, grinding the high spots and filling the low ones. But just how flat does it really have to be? Can't I just use a little thicker layer of mortar to fill the known low spots as I lay the tiles, especially if I "beat" the tiles into the mortar to assure good contact as some books recommend?
Some books and websites also stress the importance of a level slab. What's so bad about it not being level to within 1/4" per 10 feet?
My slab is at grade.
Thanks,
Ray