White Patches on Ski Bases: What are they?

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General

Frequently we are asked about "white patches" appearing on ski (or snowboard) bases. These are not a figment of imagination. People are often puzzled by them appearing. The white patches most often appear during colder weather or after a very long ski (say, 40+km). When consulting others most people are given one answer. However, there are several possible answers.

Here's a point form list of possibilities in no particular order or likelyhood that it matches your "white patch".

Note also, please, that you can experience more than one of these possibilities at the same time (e.g. base burn and excess wear).

We cover these points below and at the end describe some possible solutions.

Base Burn

Base burn is when the base material is transformed. (You may be interested in reading our Tech Page on Base Material too). For racing and better recreational skis the base material is a form of polyethylene known as UHMW-PE (Ultra High Molecular Weight PolyEthylene). "Entry level" skis and the most snowboards use another form of PE called HD-PE (High Density PE). The most oft used name for UHMW-PE is the brand name "P-Tex". There are a couple other brands. Depending on the mix used to make the P-tex the melt point can be as low as 125°C and as high as 138°C. Easily within the temperature range of the iron when most waxing happens. But most of this iron heat gets absorbed by the wax or core of the ski before the P-tex temperature rises enough to reach its melting point. This is one of the reasons to keep the iron moving and not skimp on wax. When UHMW-PE does melt it is transformed into HD-PE. The two materials, though both PE, are formed differently at the factory. UHMW-PE is formed using pressure rather than (direct) heat. UHMW-PE leaves enough space between the PE strands for wax to flow into it for a small distance (small in human terms). HD-PE allows virtually zero flow penetration.

Since UHMW-PE is not perfectly uniform across the entire base and cumulative ironing actions over time are not consistent, base burn usually appears in small patches. HD-PE can only be surface waxed -- none of the wax penetrates into the base as it does with UHMW-PE. And surface wax is the first wax to get completely worn away. In abrasive snow conditions (very cold snow or man-made snow) the wear will happen much faster. With the wax removed from these patches the patches turn a light grey to white colour.

The majority of ski bases are a black colour because of the graphite (which is black) added to the base mixture. Base burn can happen to clear bases as well. But it is much more difficult to see.

You cannot "undo" base burn any easier than turn back time. However, in most cases the base burn is not very deep. The shallowness of most burns means there are work-arounds. The worst base burn I've ever seen was so severe that the base had melted away from the ski and formed a large bubble! It was jokingly referred to as a "racing bubble". If you too have formed a racing bubble then there is no workaround.

The principal fix/workaround is to remove a thin layer of the base surface not only for the area of the patch, but around it as well. You can do this with a sharp steel scraper, with sandpaper or with a base grind. Which to choose is up to you. Using a steel scraper requires some deft skill. Using sandpaper is easy and requires less skill, but is more time consumptive. Base grinding can be quick if you have immediate access to a grinder but is the more expensive solution. Of course you are always free to decide that these skis are now your training or "rock" skis and go buy a new pair.

You can help prevent base burn by:

Excess Wax

Having excess wax is the best result of any of the choices. If you take a brush and polish the white area and the whiteness goes away then this usually indicates that it is wax. If the whiteness remains then it would likely be the "hairies" (raised strings of P-tex) or base burn. With wax there are several possible reasons:

  1. You may not have brushed this area enough. This is pretty common with the harder, colder waxes. Hard waxes are longer molecules and can spin out of the base form white patches. Try brushing the area lightly with a brass or copper brush to 'break' the surface before a long brushing with the nylon brush. For help with waxing cold waxes please refer to our web page on Cold Glide Waxing.
  2. You may not have scraped/brushed this area well enough because there is a dip in the base. Looking at this area with a steel square at several different angles should show you if this is the case. In this instance a "good" grinding of the base can level the base out. A poor to bad grind of course could make things worse. You can do this repair with a steel scraper and some skill too.
  3. You may have an area that is really amorphous. The P-tex has lots of these areas that are often small. You may have a large area there. These areas absorb more wax. The P-Tex expands and contracts as the temperature changes. On really cold days the base contracts more. With the colder wax being of larger molecule size than warm wax it will be squeezed out more in cold conditions. The wax will be more visible because it spins out (similar to cotton candy). This relates to (1). So with cold and very cold wax it's recommended that the skis get brushed, set outside to get cold (shrink the base) for a good while and then brush again (as suggested with (1)). Can grinding help? By removing the amorphous area it might help because there is potentially less ability to absorb wax in this area into the base.
  4. The wax, particularly the colder waxes, may not be held to the base very well. So the wax is sitting mostly at the surface with little to anchor it to the base. So it pulls off and spins and wears away more easily. You may need to be doing better base preparation (read the Tech Page on Base Preparation for more information). If the conditions are very cold it is also possible that you are not using a wax that is tough enough for the abrasive conditions. For example, if you are skiing at -18C then Toko Blue is not a good choice by itself. Toko Blue just isn't tough enough for -18C. A hardener overtop (such as Toko Xcold) or another brand (Ski*go C380 or Vauhti 30F) of wax is what is needed. You should read the Tech Pages we have on glide waxing, cold weather waxing and base preparation. These have links off the SkiWax.ca main Tech Page (near the bottom).

Hairies

"Hairies" is technical slang used by skiers to describe very fine bits of base material hanging off of the base. Since the PE material is tens of millions of atoms long it is pretty easy to have material hanging out. The "average" length of a single PE strand ranges from 1 to 1.5 km. You are unlikely to be seeing at the molecular level with your naked eye, but you can see hairies with the naked eye or low powered magnifying glass because the PE strands clump and weave together.

With hairies you can cut them off with a sharp steel scraper or a razor. Follow up with a good fibertex'ing. Fibertex is designed to cut rather than pull material. You want to cut hairies off because they will drag in the snow. A small amount of hairies can significantly slow a ski.

Before deciding that your condition is hairies, check that the cause is not excess wax by brushing the area with a nylon brush. If the white patch goes away then it is excess wax. If the white patch stays then it may be hairies or it may be excess wear. Excess wear over a long time period can create hairies. So while cutting the hairies off solves the problem in the immediate sense, the underlying cause will not be corrected.

Excess Pressure or Wear

Excess pressure at one of more points on the ski will mean an increase in wear in this area. The wax will be worn away faster. Typically this is seen on the base just under the skier's heel or mid-foot. With Nordic classic skis and the diagonal stride ski technique this is commonly seen because of the longer amount of time spent gliding on one ski with all of the skier's weight on that one ski. Excess wear can also be typically seen on the edges of skis (Alpine and Nordic) and snowboards. At the edges this is usually a reflection of very abrasive snow conditions that occur with man-made snow, very cold/hard snow or very aged (corn) snow.

The cause of wear just under the foot is usually weight. If you are carrying more weight than usual you may be over pressing the ski's camber (negative camber). You should test the camber of your skis with the weight that you will be skiing. So if you are doing the Canadian Ski Marathon with a backpack you should get skis to match. Otherwise you will use a lot more energy to go the same distance. Even an occational skier will benefit with skis match their weight because it will make for a more enjoyable ski. A ski that was bought some time ago may not match a skiers current weight that has snuck up over the past several years. Potential solutions are to reduce weight or use skis that match better to the weight you will be skiing. Having a ski that matches your skiing weight (you plus all your gear) will result in a ski that is easier to control.

Excessive wear on the edges usually is a reflection of the snow conditions. Typically there is nothing wrong with the skis. You do want to do something about it though. The longer your wax lasts the better ski you will have. As mentioned above the cause is abrasive conditions. When snow is very cold it is much harder and unyielding than at warmer temperatures. This results in the wax being worn away more quickly. Snow that has aged will have lost its nice snowflake structure and now look more like a small ice crystal. Aged snow is thus more dense than a snowflake and is more abrasive. Man-made is not the same as natural snow. Natural snow forms over tens of minutes or hours; man-made snow is formed in seconds. The resulting crystal is similar to aged snow, but with the crystal having sharp edges. This makes man-made snow the most abrasive of all until aging take the sharp edges off.

Solutions

Stone Grinding

One solution mentioned above is stone or base grinding. Stone grinding is a service. The quality of a stone grind depends on the machine, the grinding wheel and the operator. Clearly I won't know who you are considering (I'm a web page, not a psychic). In the same shop different operators will have a different level of skill. If you talk with the operator, draw him out on the technical details more about grinding, waxing, structure choices, etc. If he can't "talk" in tech I'd get shy. Ask for references (just like for a reno contractor for your house; your skis are not cheap) and follow up with several of the references. Check out several technical sources for grinding. Check out www.engineeredtuning.net for some info before talking more with the grinding fellow (no we're not affiliated; it's a useful site).

Steel Scraping or Sanding

As mentioned before, using a sharp steel scraper takes some skill. For many people this make stonegrinding more attractive. With sanding there is more time needed than deft skill. For more information on both of these please refer to our Glide Structuring Tech Page

New Skis

New skis are always an option. (No, I won't write a note to your spouse or significant other explaining that this is why you need new skis). Depending on the age of your skis and the abuse you put your skis through they might be getting near the end. Or your skis may just no longer match you due to weight or skill changes over the years. A weight change of 5kg may enough to cause a ski to no longer function well because it was already near it's limit earlier in its life.

So, are you skis too soft? too hard? maybe. Test the camber of the skis, wearing all your ski gear, to see.

Better Waxing Techniques

When snow is colder and/or abrasive the choice of wax will have a direct effect on the durability. A hardener wax is the best choice to toughen the wax on the base to resist wear. Proper application is key to getting a wax job that will last a long time. The SkiWax.ca Tech Page on Cold Glide Ski Waxing should be read.



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