To set the slope of the mortar bed, the author created mortar screeds. The one on the left will help form a drainage swale. A third screed (not shown) runs along the left side of the path, all the way to the gate.
After sweeping the grit from the slab, sponge the site of the mortar screed with clean water to remove dust and to dampen the slab.
While the Portland cement slurry is still wet, pile on a stiff mortar mixture that's four parts sand to one part cement with just enough water to combine them. Compact the mortar to the correct height and slope by tapping on a 6-foot straightedge laid along the top of the pile.
Rest one end of a 6-foot straightedge on the part of the screed that has been compacted, and tap the other end down until the uncompacted part of the screed is at the proper slope and height.
The process for floating the mortar bed is similar to that of creating the screeds. After dampening the dry slab with clean water, apply a thin coating of slurry to the slab and to the side of the screed.
Using a wood float, compact the mortar to about 1/4 to 5/8 inch above the top of the screeds. Smooth it using a flat trowel.
Holding the narrow face of an aluminum straightedge against the tops of the screeds, jiggle it from side to side while gradually pulling it to “saw” off or strike off the excess mortar.