Lay the First Wall
Prepare premixed mortar according to manufacturer's directions. Beginning closest to the house, trowel a bed of mortar along the marked lines where the cinderblocks will sit. Lay the first block by pressing it gently into the mortar. Make sure it is plumb and level.
Apply a layer of mortar to one end of the next block before butting it against the first and pressing it into the mortar (Image 1). Remove excess mortar as you work. Before completing the wall, insert sections of 1" PVC pipe intermittently between the blocks and through the wall to provide drainage.
Tip: Patio slabs typically slope away from the house, so subsequent cinderblocks may require more mortar below them to keep them level with previous blocks (Image 2).