Paco has triumphed once again! I was sceptical about the amount of material available to him, although I had scoured every bit of the garden to rescue fragments of the 'piedra'.
Always confident of the result, Paco has even surprised Christian with his workmanship. He has effortlessly worked the un-yielding material around the curve of the stairway.
Once the mortar is dry the excess will be brushed away with a wire brush, before the surface is sealed with a silicone based sealant. I will add that to my list then!