Thanks for your question.

The maximum recommended slopes for Natural Paving:

CLUTA-Garden grade

Max slope with:
Round pebbles 1 in 5 or 11 Degrees
Crushed gravel 1 in 4 or 14 Degrees

WAIAU-Car grade

Max slope with:
Round pebbles 1 in 6 or 9.5 degrees
Crushed gravel 1 in 5 or 11 degrees