Brushing skis is mostly done with the glide zones of the ski. This page only covers brushing the glide zones of a ski.
Brushing can be done at a number of different stages during the ski waxing process. At all of these stages the purpose of brushing is to expose the macro and micro structure of the ski base. A ski base waxed properly with the ski base's structure exposed will go faster.
There are a number of different structures that can be placed into a ski base. These structures can be added by stone grinding, sanding and rilling. Different structures work better than other structures for certain conditions. So a ski with a "coarse" structure with large rills is best for a very wet snow. In contrast a very fine structure with no rills is best for very cold fresh snow.
With these structures there are "macro" structures that you can see easily with the naked eye. There are also "micro" structures that are more difficult to see with the naked eye; a magnifying glass of reasonable power can usually allow you to see the micro structure. These micro structures can best be described as little mountains and valleys in the ski base.
Different brushes' bristles have different diameters and different stiffnesses. All brushes have no problem removing wax from the tops of the structural mountains. But how far down into the valleys each bristle can go is determined, primarily, by it's diameter. The smaller the diameter of a bristle the less stiff it becomes and the less effective it is for removing wax. This becomes more obvious as the wax to be removed is harder. To balance the smaller diameter versus stiffness different materials are used for bristles. Nylon is often used since it is low cost and has a long lifespan. But nylon is only stiff enough at larger diameters. Horsehair has a natural diameter than is quite small and is reasonably stiff. Both nylon and horsehair are good at not altering the ski base structure. Brass or copper is the next material that can maintain it's stiffness at a diameter smaller than nylon or horsehair. However, brass/copper tends to be more aggressive than horsehair or nylon. As such it can slightly alter the structure of the base if the waxer is too aggressive brushing. The final material is steel. There are different types of steel that can be used. By using steel bristles the diameter can be reduced even further while not losing stiffness. This results in the deepest brushing; the brushing that's closest to the valley bottoms. Steel brushes are not all alike. There are large diameter steel brushes that are designed for placing a structure into the ski base. The finer steel brushes will only affect the base structure if used too aggressively.
When you go to apply fresh glide wax to the ski to match the conditions you are going to ski you want the result to work well and last as long as possible. The closer the "wax of the day" gets to the ski the better because the wax will not as easily be worn off and expose a different wax underneath. Therefore brushing the ski before wax is applied is very important. The brush to use is one that is stiff with very small or fine diameter bristles. The brush of choice is usually a copper or brass hand brush, or brass roto-brush. There is also available a fine steel roto-brush and an ultra fine steel roto-brush which have finer diameter bristles than the brass brushes. By brushing the ski before the wax is placed on the base older remaining wax is removed and the structure of the base is exposed. By being freshly exposed the new wax will be as close to the base as possible -- even in the smallest, deepest, narrowest valleys.
Wax is now applied, allowed to cool and scraped when appropriate. It is usually best to allow the ski to rest after scraping. Especially if you have scraped a very hard, cold wax while it still had warmth. This resting period will help the ski base take up more wax.
The inital brushing is usually done with a nylon brush. This gives the swift removal of the bulk of the wax sitting on the ski base surface. The hard brown roto-brush performs the same job. But the micro structure at this point is usually not exposed unless a very coarse structure has been put been put on the base.
The next brush used is the horsehair hand brush or a finishing roto-brush (grey, white, 7mm black or fine horsehair). With the finer diameter bristles they are good at working excess wax out of the valleys. You may have heard skiers talk about how they need to "ski in" the wax job for 5 to 8 kilometers before it's effective. What these skiers are doing over these kilometers is brushing the ski bases with the snow crystals! So for 20 to 40 minutes they are brushing their skis in a very energy intensive manner. Just 3 minutes more hand brushing or 20 seconds more roto-brushing would have saved them a lot of time and effort.
Some waxes are harder than others. Ski*go Violet and Green are examples of harder waxes. These waxes are too hard for the horsehair bristles to work effectively on. With these waxes the brass/copper brush or the ultra fine steel brushes are used lightly to remove the excess wax. Their additional stiffness helps them be effective. Further cold waxes are applied to skis with a fine structure. A fine structure means the valleys are narrow which means the brush bristles need to have a small diameter.
Here is a short summary of when to use which brushes:
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with e-mail to "Askus at SkiWax.ca" (replace 'at' with '@') or
telephone (519) 747-5293.