I am building a decorative wall in my backyard with seating height(~20"). The contractor has built the wall with 6 inch cement blocks and put 12 inch red brick bullnosed tiles as caps. We are going to do a flagstone facade on the wall, but I am still apprehensive about the 12 inch tile on top of 6 inch wall. I am not sure why he chose 6 inch blocks since 8 inch blocks are more common. I do have a lot of curves in the wall, I am not sure if that is why he choose 6 inch blocks. Anyone have any comment on this? Am I worrying in vain or should I not accept this and get it rebuilt?