Many thanks all for the replies. Exactly what I was hoping for!

@skillwigee: I'd never thought of that approach for building boat hulls. I can also see that coming in useful for stone steps and possibly dry-stone walls (or garden-bed retaining walls)..

And any tips on speeding up renders are always welcome! (unless they interfere with my all too regular tea/ciggie breaks)..:-)

Cheers,
Diolma