Belaying a leader in a climbing gym with a Gri-Gri requires some skills you won't have learned if you've only belayed with ATC-type devices. Luckily it's not hard to make the adjustment.
For an overview, check the Petzl technical page: Belaying with the GRIGRI
The big thing to learn is how to momentarily allow rope to be pulled through the GRIGRI without blocking the cam's action.
- Hold the rope with at least three fingers.
- Use the index finger to support the GRIGRI
- The thumb presses on the cam.
The action must be momentary, and as soon as the leader has clipped return to the primary belaying position.
More of a visual learner? Have a look at the official Petzl video.
The GRIGRI is a belay device with assisted braking. The belay technique is very close to the generic technique, but has a few specifics. For a climber who is already familiar with using classic devices, it takes a little time to adjust. The technique described here is the only one that Petzl recommends. This technique offers real advantages in terms of safety: - the rule to never let go of the brake side of the rope is respected - it allows to transition between "giving slack" and "giving slack quickly" without letting go of the rope - in case of a fall, the belayer doesn't clench the cam A tip for easier belaying with the GRIGRI: keep the free rope stacked near you. More info about belaying techniques, on www.petzl.com/belaying