[Cob] Why soak lime?

[Lance Collins]

I've got my experimental wall up inside my shed.  It's a bit rough where 
I've laid blocks so I've started rendering.

For the scratch coat I have mixed sieved sub-soil, sawdust and powdered 
hydrated lime (9/9/2) with water to give a slightly sloppy mix.  It sticks 
well to my wall and the worst cracks are about 1 mm where the cover is 
about 5 mm.  Now I've made a wash of 3 parts soil to 1 part lime and 
brushed this over the scratch coat.  The cracks have closed nicely and a 
wet cloth rubs up a smooth finish.   It all looks pretty good  for a first 
attempt.

The wall is not professionally flat  but it looks OK for a mud wall.

So what problems can I expect from not using lime putty and sand?

Lance