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.

How deep can waxes penetrate into the ski base?

Waxes penetrate into the ski base, however, the penetration depth is very small, according to many different research studies the penetration depth is max. 1 micrometer, 1.000 nanometers.

Regardless of research study results the value of max. 1 micrometer, 1.000 nanometers for wax penetration into the ski base material seems to be very realistic.

• the top surface of the ski base is created by NANO fiber-like structure where wax molecules are accommodated in free cavities, the normal length of the NANO fibers or depth of the NANO fiber-like structure is ca. 250 nanometers
• in this “open” top surface there is enough free space to accommodate wax molecules
• inside the NANO fiber-like structure which depth is ca. 250 nanometers are cavities and free spaces in the size of a few tens of nanometers whereas the size of individual wax molecules is amounting to a few of nanometers
• in this “open” top surface the most of wax molecules are accommodated
• some wax molecules can also penetrate a bit deeper into the ski base but only in so called amorphous regions inside the bulk polymer, crystalline regions cannot be entered by wax molecules
• below the open top fiber-like structure, i.e. in the bulk polymer the free cavities are - however - much smaller (typical range for UHMWPE is 5 to 20 nanometers)
• at the same time the crystalline region fraction is much higher in the bulk polymer (ca. 70 to 80 per cent) compared to the open top surface (50 to 60 per cent)

Most of wax molecules are accommodated in the open top surface which is not much deeper than 250 nanometers. Wax molecules can be retained between the NANO hairs. Wax molecules and NANO hairs of the polymer create the so called gliding surface.

What are the main weaknesses of waxes? Part no. II – wax softness

Waxes are normally soft, much softer than the material of the ski base. Even if ski wax manufacturers try to mix hard waxes for abrasive and aggressive snow conditions, waxes are normally softer than the ski base itself.

 

If softer waxes are mixed with the ski base material in the top surface of the ski base creating the mixture called gliding surface, the result is always softer surface of the ski base or softening of the ski base surface by adding the wax.

 

The hardest waxes offered currently on the ski wax market like Toko X-Cold Powder / Blue X-Cold, Holmenkol Ultra Base Cold, Swix CHX4 / HSX4 / PS4 (cold powder blue/green series), Maplus Race Base Cold – reach the hardness 40 to 50 shore D which is still below the hardness of the ski base which is normally 65 shore D.

 

If we consider that the wax absorbing capacity in cavities inside molecular structure of a ski base is ca. 5 to 30 % of the thin top layer of the ski base, we can say that on the surface amounting to max. 255 cm2 and min. 38 cm2 of the total 765 cm2 the hardness is reduced by ca. 23 to 38 per cent.

 

If we consider that especially the hardness is the most important factor influencing the gliding qualities or friction especially in cold, hard and abrasive snow conditions, then it could mean that wax application under these conditions is contra-effective.

 

Fortunately for ski wax manufacturers, the question is not as straightforward as it might seem at first glance. It is true that the application of soft waxes reduces the entire hardness at least in the extent where wax molecules are accommodated inside the ski base material. On the other side ski base is protected and intermolecular bonds between ski base surface and snow surface can be blocked thanks to wax application.

 

We need to apply waxes also under cold, hard and abrasive snow conditions to protect the ski base and block intermolecular bonds. At the same time wax application will always decrease the ski base hardness. Especially the hardness is the most important factor influencing the gliding in cold and hard snow conditions.

What are the main weaknesses of waxes? Part no. I - wax bonding to ski base

Ski waxes are for sure the most popular and most common agents to optimize gliding features for particular snow and weather conditions.

For each snow condition and for any temperature range there will be many different waxing options to be used.

What are - however - the main weaknesses of waxes especially in competition ski service?

The main weakness of ski waxes is the way how they connect with ski base.

Even if this statement sounds very theoretically, the consequences are practical and enormous.

Ski base consists of PE molecular chains enriched with different additives in NANO level. PE molecular chains create on the ski base surface a fiber-like structure with many small cavities and free spaces. If we consider that the normal length of NANO-fibers on the ski base surface is amounting to ca. 150 to 350 nanometers, the size of cavities can be estimated in the range of a few tens of nanometers. This is enough free space to accommodate wax molecules, especially if they are highly-mobile due to liquid state by ironing.

Fiber-like structure on the ski base surface and wax molecules accommodated in the free cavities inside the fiber-like structure create a new gliding surface on the top of the ski base which is a mixture of the fiber-like structure and wax molecules.

Already this new gliding surface is more a mosaic consisting of different PE-stones, wax-stones and additive-stones. Imagine what will happen if a second / third / forth etc. wax layer is ironed on the mosaic-like gliding surface... The diversity and variability of the gliding mosaic will be increased dramatically.

After wax application - especially if more wax layers are applied - a unique and original surface is created on the top of ski base. This gliding mosaic-like surface is so unique that it cannot be repeated twice. Most probably on each ski of one ski pair a different mosaic-like gliding surface is created. This is very probably the reason why competition ski service is more magic and spells than science! Results can be hardly repeated!

What is crucial to achieve a reliable kick? Part III.: correctly defined kick area of the ski

In the article "What is crucial to achieve a reliable kick? Part I.: right stiffness and length of the skis” it was explained that skis base for classic cross-country skiing style consists of three parts / areas, two gliding areas (one in tip and one in tail of the ski) and one kicking area (in the centre of the ski).

If the skier is standing on both skis, in other words skier’s load is transferred to both skis equally, the middle area (kicking area) should not touch the snow surface and the skis should glide on the snow surface in the tip and tail areas (gliding areas).

In the opposite if the skier concetrates his/her load on one of both skis, the middle area is pressed down and get in touch with snow surface enabling the kick.

For a reliable kick is thus responsible stiffness and length of the skis (they must correspond with the weight and height of the skier) but also the length and position of the kicking area.

If the kicking area - where kick waxes are applied - is A. wrongly positioned along the ski or B. too short or too long no reliable kick can be provided.

If the kicking zone is correctly positioned, but too short the consequence is missing kick but still good gliding properties.

If the kicking zone is correctly positioned, but too long the cosequence is A. a reliable kick but bad gliding properties or B. freezing wax with no kick and horrible gliding properties or C. skis do not enable any movement.

If the kicking zone is incorectly positioned, the result is normaly too long kicking zone with consequences A / B / C depending on other factors as snow conditions, wax type etc.

Conclusions

Define the kicking area where kick waxes are applied carefully before you start to ski. If you do not know the kicking area, apply the kick waxes in a short window which can be increased with insufficient kick. In direction to ski tail the kicking zone ends latest where the ski boots end. If you need to improve kick properties by enlarging the kicking zone, go direction to tail first and stop at ski boot end. After you have reached the ski boots end, enlarge the kicking zone in direction to tip.

How the wax application changes the ski base structure?

Especially competition skis are structured for better gliding performance. After the ski base grinding process has been highly automatised, the structuring is booming. There are various structures for any snow conditions and temperature range. Each parameter of the structure to be grinded can be set up, endless shapes, depths, pitches, angles are possible. Structures become more and more complex and highly specialized. Any detail, any parameter is important and counts...

Is it really true?

It is true that the modern grinding machines can produce almost any structure form and shape which you can even imagine. The grinding machines are extremelly precise and fast. Fine and high-quality stones are formed with diamant pins with accuracy to hundredths, pressure, feeding and revolutions can be controlled and regulated so precisely and stable that structures can be perfectly cut.

On the other side each ski base material is a bit different even if it was produced in the same production batch, but these differences are quite small.

After ski waxes - in multiple layers - have been applied on the structured ski base, a new story beginns to be written. Frist ski waxes and ski base material connect or are mixed on the molecular level to a new material which is a mixture of both wax and ski base material creating a new layer which can be called “gliding surface”. This new gliding surface is created on the molecular level chemically but in daily ski service reality it is created on macro or micro level. Thin wax layers in different forms are applied on the ski base, ironed, excess wax is scrapped off and brushed out of the structure...

Excess wax is brushed out of the structure, structure is restored by brushing, original grinded structrure is revealed again with help of brushing...

Is it really true?

Let us analyze a common case: grinded linear grooves with the pitch distance 0,5 mm which is normally called fine to middle coarse structure.

The pitch distance 0,5 mm which is 500 microns will correspond to ca. 50 microns deep structure, the ratio width / depth is ca. 10 due to technological reasons. Standard linear grooves are V-form grooves, the pitch distance between the tops amounting to 500 microns will correspond to a width amounting to few microns in the bottom (depth ca. 50 microns).

If excess wax is removed, it is first scrapped off by scrappers, later brushed out of the grooves (V-form of grooves is restored by brushing again. Which brush is used to restore the structure / grooves filled with wax?

Standardly steel or bronze brushes are used to clean the wax out of the structure. Both steel and bronze brushes consist of bundles of bristles. Bundles have normaly circle-shape with diameter ca. 5 mm. Each bundle consist of equally long and thin bristles. Standard steel and bronze brushes used to reveal structures have bristle length of ca. 20 to 25 mm and diameter of 100 microns (0,1 mm).

Let us have a look at the situation when the excess wax is brushed out of the grooves a bit more detailed: we have grooves 500 microns wide and 50 microns deep, we have brush with bundled bristles 25.000 microns long and 100 microns wide.

Conclusions: standard steel brush will remove the excess wax out of the upper half of V-shape grooves with pitch distance 500 microns. The bottom area of V-shape grooves with pitch distance 500 microns and depth 50 microns will remain “filled” with wax. In addition the bristles with the diameter of 100 microns will work as a rammer and will compact the wax inside the bottom area of the V-shape grooves resulting in shallower and more rounded groove forms.

Application of ski waxes does change the ski base structure, waxes make the structure shallower and more rounded compared to the status after fabrication.

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.

For whom is mohair the right choice?

Background of Mohair - alternative for kick waxes

Kick waxes are used for classic cross-country skiing style enabling forward movement on skis in the ski track. Unlike the skate style, the classic cross-country skiing style requires the use of an agent enabling the “kick”. To enable the “kick” and thus the forward movement in the classic cross-country skiing style kick waxes - as hard waxes or liquid waxes - were used for many years.

Problems with kick waxes

Kick waxes - especially the liquid ones - are hard to be applied on the ski base. There are plenty of kick waxes for different snow types and temperatures ranges. Use of kick waxes was connected with many troubles = they did not enable the “kick”, they froze and rubbed off while sliding...

Skate style

All these problems of kick waxes accelerated the development of the skate style where no kick waxes need to be used. We could also say that popularity of the skate style originates in the problems of kick waxes.

Problems of skate style

Skate style can afford advanced skiers only and skiers in a good physical condition. If you are skiing uphill in skate style, you have no support of the kicks, you need to skate and glide up to the top of the hill which can be very challenging especially for untrained skiers.

Other alternatives for kick waxes

Especially the high requirements for physical condition and skills in the skate style re-started the search for other alternatives for kick waxes as it was clear and obvious that skate style is not the right option for ski tourists. Beginner skiers and especially ski tourists need for their cross-country skiing trips the kick to move slowly and comfortably in the country. They are ready to give up some of the gliding qualities - if skiing downhill - for a reliable and easy kick - if skiing uphill.

Mohair as a modern alternative for kick waxes

Mohair seems to be the right solution for these tasks. It worsens the gliding qualities of the skies acceptably and in the most of snow conditions it provides a more or less reliable and easy kick enabling an easy and comfortable forward movement on skis uphill.

Mohair limits and problems

Especially in cold and icy conditions and in very wet spring snow conditions mohair cannot provide a reliable kick because there is nothing to catch the hair on. In cold and abrasive snow conditions mohair can be worn quite fast. In moist snow conditions close to zero mohair can have the tendency to freze and needs to be protected by anti-freze agents.

Despite the limits and possible problems mohair seems to be a very good alternative for kick waxes especially for ski tourists and beginner skiers.

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!

WHY MAN-MADE SHOW IS EXTREMELY ABRASIVE?

 Why Man-Made Snow is Extremely Abrasive?

You noticed for sure that the so called man-made snow is much more abrasive than the natural types of snow. Man-made snow is used in alpine resorts (on ski slopes) more often than in nordic areas (XC tracks) but currently it is the most common snow type especially in lower regions.

Especially if the temperature is deep under zero, the man-made snow is so hard and so abrasive that you can have the feeling “it is cutting into the ski base”... And your feeling is almost literally correct.

Man-made snow consists of ice grains which are small, rounded and extremely hard. Thanks to small size or diamter of individual ice grains the man-made snow is also extremely compact and dense - it contains small share of air compared to natural types of snow. Shortly after production man-made snow is moist to wet even if it is freezing.

What’s the reason why man-made snow is so abrasive?

The correct answer is hidden in the hardness. We mentioned that individual ice grains of man-made snow are small, rounded and extremly hard. Especially the extreme hardness of the snow grains connected with the very compact surface of the snow pack are the main reasons why man-made snow is much more abrasive than natural types of snow.

Why are the ice grains of man-made snow so hard?

The extreme hardness of ice grains of man-made snow is caused by freezing direction which is opposite to natural snow types. 

Natural snow types freeze from the center to the edges. Air humidity condenses on a snow flake nucleus (most often a dust or dirt particle) and starts to develop from the center to the edges in various forms and shapes.

In case of man-made snow a small water droplet is flying out of the snow cannon and meets the cold air, at the moment as the water droplet gets in touch with the cold air, a thin ice shell develops on the outside perimeter of the water droplet, while the middle remains filled with water. Ice grains of man-made snow freeze from the outside to the center gradually. Liquid centre is locked in a ice shell.

If water changes from liquid to solid state its volume increases slightly. Water locked in a ice shell cannot increase the volume resulting in the increase of density. Increased density means increased hardness.

Increased density = increased hardness of ice grains of man-made snow is the main reason why man-made snow is so extremely abrasive.

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.