Why grind in the first place?
For skiers that race, this can be a big performance booster. In general, stonegrinding removes a thin layer of damaged base material, reexposing clean polyethylene. This results in the best wax retention.
As well, a stonegrind etches a series of lines/broken lines onto the ski base producing a purposely designed, structured surface to better control snow crystal shape and moisture content. These two elements left unmanaged can produce excessive friction, inhibiting glide.
*Keep in mind, a stonegrind will not improve the performance of a poorly fit ski. As well, a stonegrind will not improve the performance of an incorrectly flexed ski chosen for a given snow condition. Ie soft shovel for a hard track or stiff hinge for soft track.
How often to stonegrind is contingent on your waxing skill and frequency as well as the kinds/quality of snows your skis are exposed to. A skier/racer able to recognize the optics of base damage and other factors will on average have their skis ground every one or two years.
How many times can a pair of skis be ground?
The answer to this is a moving target. Some skis come in highly heat damaged or excessively out of true—most frequently base high found on specific areas of the ski base. These skis require a high amount of material removal (up to a point) thus significantly reducing how often they can be ground.
Assessing the ski before grinding will give the grind tech a general impression of the work needed to be done. But once the ski is put over the stone, only then can the tech truly know the amount of work needed to flatten and reveal clean polyethylene.
A full grind for a typical pair of skis, on average, from start to finish, will require up to 10 passes, each ski, over the stone. Doing the math for how often a typical pair of skis can be stoneground is plus/minus 5X’s ish.
Why grind touring/non-racing performance skis?
For these groups of skiers, a stonegrind serves to clean up a battered base making it easier to apply and scrape glide wax. In the case of a non-racing performance skier, a stonegrind provides the same ease of waxing and, like a racer, greatly improved glide.