In reply to TobyA:
Hey Toby,
Maybe check the product info on the grigri....
1. Field of application
Belay device for 10 to 11 mm (9.7 mm is acceptable) CE (EN 892)
and/or UIAA certified dynamic single ropes (core + sheath).
The GRIGRI is designed for indoor wall climbing or for rock climbing
on well-protected routes where anchors meet the EN/UIAA standard
(25 kN). It can be used to belay and lower a leader or a second.
It should not be used for mountaineering or adventure climbing.
All new ropes are slick with a grigri and my 9.7mm rope after breaking it in now works perfectly with a grigri.
Cheers
Craig