What is the main difference between cold and wet ski base?

Competition skis or racing skis are normally offered with three different types of ski base: cold ski base for cold, hard and abrasive snow conditions, wet ski base for wet, soft snow conditions with water film in the interface and universal ski base for transmission snow conditions between cold and wet.

Ski base compositions differ in used additives to comply with different snow conditions.

Soot or carbon black in cold ski base types is used to increase hardness, wear-resistance.

Graphite in lamella form in cold ski base types is used to improve gliding features and electric / heat conductivity.

Metal oxides in cold ski base types are used to increase hardness and wear-resistance.

Molybdenum disulfide in wet ski base types is used to improve water and dirt repellency.

Wax like additives in wet ski base types are used to improve gliding features.

Are the different additives used in cold and wet skis the main difference between cold and wet ski base types?

I would say NO, they aren’t...

I would say that the main difference between cold and wet ski base types is the different ratio of crystalline and amorphous regions and the different wax intake capacity.

UHMWPE which is the main material used for production of racing ski base types is a semi-crystalline polymer which consists of crystalline - for waxes and any additives inaccessible - regions and amorphous regions where the most additives are allocated and where wax is connected with the ski base. Crystalline and amorphous regions are normally separated by transsition regions which are - compared to micron-sized crystalline and amorphous regions - in nanometer scale.

Cold ski base types have the majority of crystalline regions which are harder, compacter and more wear-resistant, but cannot absorb any additives and waxes (thus they are more or less pure UHMWPE), wet ski base types have higher fraction of amorphous regions which are softer, modified by additives, contain cavities to absorb waxes...

How does the wax stick to the ski base?

It is common knowledge that ski bases are waxed. Many wax manufacturers offer liquid waxes where the wax is dissolved in a rapidly evaporating agent. With a sponge you just apply liquid solution of wax and solvent on the ski base and after the solvent evaporation your ski is ready to be used with improved gliding features!

Is it really true?

To answer this question, we need to understand how the wax sticks to the ski base. Does it stick by chemical bonds or by mechanical retention?

The way how waxes stick to the ski base depends especially on the type and features of the ski base. Cheaper extruded ski base types do not have NANO fibril structure to retain waxes mechanically, thus they need to stick to the ski base by chemical bonds only.

 

Chemical bonds are – however – very weak, thus the abrasion resistance of such a wax layer is very low. In other words: a wax layer – especially liquid wax layer – applied on the cheaper extruded ski base will wear off in several hundred meters or max. kilometers depending on snow conditions.

 

More expensive sintered ski base types have NANO fibril structure on the very top surface to retain waxes mechanically, thus waxes are mixed with the base material to a new layer consisting of both wax and ski base material.

 

Mechanically retained wax molecules are protected against abrasion forces, thus their life time is relatively good. Mechanical retention is – however – supported by heat, thus hot wax application is recommended here. Cold liquid wax application will hardy penetrate deep enough.

Conclusions

Waxes stick to cheap extruded ski base types by weak chemical bonds only with very low life time of wax coating. Waxes stick to more expensive sintered ski base types by mechanical retention with good life time. Liquid wax application seems to be waste of money in both cases.

What is crucial to achieve a reliable kick? Part II.: the right ski base

In the previous article we explained that the right stiffness of the ski for classic cross-country skiing style is the first crucial parameter to achieve a reliable kick.

Today’s part is dealing with the ski base.

We know that the ski base consists of three areas in case of skis for classic cross-country skiing style. In the front and back there is the gliding area, in the middle there is the kick area. In the front and back gliding waxes and agents are applied, in the middle kick waxes or means are used. Alternatives for kick waxes are mohair, kick strip, zero ski base patterns etc.

Ski base is responsible for both gliding and kicking properties.

Kicking features

It can be very surprising but kick waxes or kick means decide not only about how reliable the kick is but also how well or badly the skis glide.

Why?

If a liquid kick wax is freezing or a hard kick wax layer is too thick, this bad kick quality is impacting the gliding qualities so significantly that any gliding wax can compensate this.

If you are a beginner skier or ski tourist you need to concetrate on the quality of the kick agents because they influence both gliding and kicking properties.

Gliding properties of kick waxes depend especially on

• correct position and length of kick area
• thickness of kick layer
• right kick wax needs to be chosen for specific snow conditions
• roughness of ski base in area where kick waxes are applied needs to be increased

Gliding features

If kick wax does not glide well, the ski does not glide well :-) You can improve the gliding features with the application of gliding waxes and agents, but they protect more the ski base than improve the gliding features in case of classic cross-country skiing style.

In addition there are ski base types which are able to absorb and “hold” gliding waxes and there are ski base types on the market which cannot absorb or hold any wax.

How often should be competition skis re-grinded?

There are two extreme positions related to the wear and life time of ski base structures existing next to each other.

First we need to define what is the ski base structure for the purpose of this article?

Ski base structure is any type of stone-grinded structure for the purpose of this article. We do not question that also other manufacturing methods exist to produce ski base structures as e.g. imprinting, belt-grinding, rilling... For us these methods are - however - so unstable and create so varied results that we do not want to discuss them here.

Stone-grinding

If a ski base is stone-grinded, old structures, small defects and oxidated or thermally damaged layer of the ski base are removed first. Normally a few tens of micrometers are removed in this preparation steps.

In the second step the ski base is flattened with a very fine stone to achieve the best structuring result. In the last step the required structure is grinded in many movements depending on the shape, width and depth of the selected structure. Multiple structures are not considered here...

Best performance of stone-grinded ski base

If competition skis are stone-grinded, they need to pass another long trip before they achieve the best performance...

First the ski base needs to be cleaned to remove cooling and greasing agents, grinding residues and dirt. Then the ski base needs to be waxed several times to clean the cavities inside the ski base. After waxing, ironing, scrapping off excess wax and brushing the skis need to be used on - if possible - fresh crystalline clean and abrasive snow to remove the “unwanted” hair and homogenise the ski base surface.

Here we are already touching our main topic slowly...

Ski base wear

Crystalline cold snow is abrasive and can remove the unwanted hair which is the side effect of the grinding process where molecular chains of polyenthylen are cut and material is removed to create grooves of different shapes. If unwanted technological hair can be removed by abrasive snow, it means automatically that also “wanted” hair of the ski base is subject of abrasion and removal.

If both “unwanted” and “wanted” hair of the ski base is subject of abrasion, it means automatically that ski base wears when used. The more abrasive the snow condtions are, the faster the ski base wears off.

Two contradicting positions

Position I.

Even if ski base structure is protected by ski wax which penetrates inside the ski base, the ski base and the structure on its TOP wears quite fast. The optimal gliding features of a specific structure are less than ca. 100 km on abrasive snow. In other words: after ca. 100 km of use on abrasive snow the structre is worn so significantly that grinded structure loses its optimal gliding features.

Position II.

If skis with a specific ski base structure performes optimally for certain snow and weather conditions, they need to be protected with ski wax application but never re-grinded. Even if the ski base structure wears slightly after each use, the optimal conditions should not be changed. Re-grinding will never restore the original quality.

What do you think, what is true and what is superstition only?

WHY FRESH POWDER SNOW DOES NOT GLIDE AT ALL?

 Why skiing on fresh powder snow is so challenging?

Fresh powder snow or freshly fallen snow at temperatures below zero and low relative air humidity is extremely challenging for gliding and low friction coeficients.

Why?

Powder snow is crystalline, in other words: individual snow flakes keep their original sharp shape. If they brake during slope or track preparation by pisten bully new sharp edges, tips and forms arise. 

Powder snow contains a high share of air resulting in surface changes of the snow if skis are gliding over it. Such surface changes lead to brittle deformations of crystalls again.

Result:

Sharp, hard, brittle snow crystalls which brake and do not connect to snow pack. The surface of the snow is extremely fragmented - similar to a stone field resulting in few and very small contact points between snow and ski base surface.

Few and very small contact points between snow and ski base surface lead to high pressure in the contact spots. Small contact points, high pressure, sharp / hard and brittle crystalls create a combination responsible for very high friction between snow and ski base surface.

The lower the temperature, the higher the hardness of snow crystalls. At a certain point (for normal ski base types = HDPE at ca. -10 degrees C, for competition ski base types = UHMWPE at ca. - 15 degrees C) the hardness of sharp crystalls exceeds the hardness of the ski base resulting in ski base plowing effect.

Under such conditions you will not want to ski...

Conclusions:

If fresh powder snow is fallen deep below zero, stay at home instead of skiing! If you need to ski in fresh powder snow on a slope, protect your ski base with a hard and hot applied wax coating. If you are a nordic skier, protect your ski base and try to improve the gliding properties the best possible way otherwise your trip can turn in a nightmare - apply hard protecting wax hot with a hot powder coating and liquid speeder!

HOW TO SELECT THE CORRECT SKI BASE?

 How to Select the Correct Ski Base?

Most of normal skiers - does not matter if alpin skiers or nordic skiers - know the black ski bases which are the standard in the last ca. 30 years.

The black colour of the ski base is caused by soot which is added directly to the ski base material.

Why SOOT and what are the main advantages of the black ski bases?

• soot is cheap
• soot has the correct NANO size
• soot is a type of dry lubricant
• soot as NANO particles is hard
• soot is conductive
• soot improves grinding
• soot can help to repell dirt 

In other words:

• black ski bases are usually harder than the transparent ones
• black ski bases are more suitable for colder conditions due to higher hardness and lower electrostatic charge
• black ski bases can be grinded more efectively and precisely
• black ski bases can repell dirt better that the transparent ones

Special advantage of black ski bases:

If they wear due to intensive using especially on abrasive cold or man-made snow types, they change the surface colour to grey or white gradually. This is a clear sign that they need to be maintained / serviced.

Black ski bases have also some disadvantages

• they abrosb normally less wax than the transparent ski bases
• they can be less hydrophobic or water-repellent than the transparent ski bases
• dirt which is normally dark is hardly visible on the black surface

Conclusions

Black ski bases perform very well especially in cold conditions. They are more universal than the transparent ski bases. In wet and very wet conditions hydrophobity of black ski bases needs to be improved by water-repelling waxes. For normal alpin and nordic skiers the black ski base is usually the right choise.