Tom’s Musings | Stonegrind 101, Polythene Pam

It’s late December in Minnesota. The high school XC race season has begun, masters racing is not far off, and touring skiers should be finding consistent snow soon. XC racers are a driven bunch, some anal to a fault. Nevertheless, for any committed XC racer, stonegrinding their race skis is an understood tool used to create fast skis. For those confused or unaware of the need for stonegrinding, I can take you by the hand and walk you through.

What is stonegrinding?

Stonegrinding is a three-step process:

i. Flatten and remove damaged base material

ii. Polish the base

iii. Structure the base

One at a time, your skis are manually fed into this machine, sandwiched between a rotating water fed stone from below, and a feed wheel from above. The feed wheel, with a programmed amount of pressure and speed, draws the ski over the stone, whose surface has been etched using a diamond bit programmed to produce a specific arrangement and depth of lines for each step. These etched lines can be continuous, broken, angled, layered on top of each other, or left on their own. Each step is also influenced by the stone and feed wheel’s rotation speed.

All of this can kinda get wordy and leave a person looking like a deer in headlights. I’ll turn off my headlights and try to answer the next questions without too much tech speak:

Why do I want to put my skis through this to begin with? Why do I want to stonegrind?

Over time your ski base takes a bunch of abuse skiing over abrasive snow, dirt, and goo. In your basement wax room, you torture that same base with a hot iron over and over. All of this eventually adds up to a ski base that’s no longer particularly flat or maybe unacceptably scratchy, contaminated with dirty snow stuff and now sealed. Glide wax no longer adheres to your bases very well. Your skis don’t want to glide like they used to. The bases will look fatigued and dull. They’ve lost their dark deep shine. For a XC racer in particular looking to maximize their race performance, this is a big deal. By reconditioning your ski base with stonegrinding, you can eliminate these issues from your go-to list of excuses for why your Mora Vasaloppet race stunk.

As the guy that’s going to bring your skis back from the brink, the amount of polyethylene (ski base) removed to get the ski to where I want is based on the goldilocks rule—not too much, not too little, just enough. Your base only has so much polyethylene. An FYI: some skis come in with significantly convex (high) spots in the bases. I can only run those skis so many times across the stone and still leave enough base. Meaning, I’m probably not going to get them completely flat, but good enough, and better than they were.

Any other telltale signs my skis should be stoneground? Like did I burn them?

A burnt base—an over-ironed or incorrectly ironed ski base—reveals itself when holding the base up to good lighting and seeing significant shiny smooth puddles. Or significant shiny smooth swathes running parallel to your ski groove, surrounded by your normally etched ski base. Sometimes you can also see an over-ironing effect when applying powders. This effect manifests as perpendicular smooth lines on your base resulting from the edge of your iron pressing powders onto your base. All of these effects, shown minimally, may not require immediate stonegrinding. But understanding how these effects happen and how to minimize them goes a long way towards keeping your skis prematurely out of my hands.

How often should I stonegrind my skis?

A consistently sliding slippery ski is a lot of fun, especially in a XC ski race. How often a particular pair of race skis have been used during the season can influence when they should be brought in for stonegrinding. Racers with one pair of skis used for all training and races will see me maybe once a year. Other racers with a quiver of skis (multiple pairs) used for specific snow conditions might follow a two-year cycle, or bring them in and ask for advice. Most dedicated racers stonegrind their skis every two years or less—certainly waiting no more than three years. With skis that I have previously stoneground during a two-year period, I can offer a “refresh” stonegrind. I need to see the skis to determine if a refresh stonegrind is appropriate, meaning that the bases are not so beat up as to require a full stonegrind. A refresh grind requires less passes over the stone, meaning less labor. This is generally enough to clean up the bases to ensure good wax adhesion (i.e. like before a big race). You can have a ski stoneground right up to a day or so before your race, and the usual turnaround time for a stonegrind is four working days, not including weekends. Emailing or calling me is best if a quicker turnaround time is needed—I am flexible depending on my current workload.

What is the prep process after stonegrinding?

I do a bunch of it for you in two different ways: after a standard stonegrind, I brush out and apply Rex Glide Cleaner to rid the base of any fluid residue and stuff from the stonegrind process. After brushing out the glide cleaner, I finish with a coat of soft base prep paraffin wax. Your job then, is to harden the base using green and blue paraffin or liquid waxes. A couple coats each, and then apply the wax of the day. If you ask for a stonegrind with prep, I do the same as above, but also do the base hardening using liquid hard waxes. Your job is to simply apply the wax of the day—liquid or paraffin.

Can you stonegrind touring skis? Or even rock skis? Or waxless and skin skis?

Heck yeah! I can stonegrind most any pair of skis. You just have to decide if the cost and stonegrinding outcome is practical. Truth be told, for the most part, stonegrinding skis is exclusive to the racing and fitness ski community, but certainly feel free to come in and ask us what we think.

— Tom Novak, Head Stonegrinder at Finn Sisu

Tonttuwerks, LLC.