Technical Aspects

The requirements of equestrian riders demand high technology surfacing solutions that can only be realised by serious materials science development. We were scientists first, equestrian people second, and we understand the necessary scientific elements that must be applied to the development of a high tech riding surface.

We've invested in continuous research and development to provide riding surfaces with the best possible physical properties. These include optimum shear strength, minimal concussion, and rebound. We have also developed scientific tests that characterise these properties so we can use objective assessment, rather than simply rely on 'feel' like our competitors.

In this section we give you an idea of the science and technology that goes into designing, installing and maintaining Attwood's unique equestrian surfaces. This is just a snapshot of what we know, and more importantly what we're prepared to share with the 'outside world'. We feel our scientific knowledge gives us the edge over our competitors, many of whom might know all there is to know about horse riding, but know very little about materials science.

Types of Footing

Equestrian surfaces or footings, come in a myriad of forms. A simple classification will identify a number of groups.

At the low performance/low cost end is Wood Chips which are pieces of wood, usually waste from a lumber process or 'recycled' natural wood products. It is considerably cheaper than sand-based surfaces but in our view significantly inferior. Disadvantages are very low levels of grip (bordering on the dangerous at times!), the chips can biodegrade very quickly, and when dry can easily be displaced from the arena.

Also at the lower performance/lower cost end is Rubber pieces. These surfaces consist of various sizes of rubber pieces, sometimes with other materials attached such as fabric backing. Recycled rubber pieces, particular from recycled tyres offers a cheap method of imparting some shock absorption and rebound properties to the surface. However, rubber contributes very little cohesion, otherwise known as shear strength, so footings can feel slippery and lack support on cornering, jumping and landing.

A second disadvantage is that an uneven surface can very quickly form which can be quite damaging to a horse's joints (not to mention humans who can suffer twisted ankles!).

Sand-based surface is by far the most popular, and if formulated correctly, highest performing surface. These surfaces can be classified into two types: coated sand to be used without water,& uncoated sand to be used with water. Each of these types usually has some kind of additive incorporated.

Coated surfaces rely on the coating to stick the sand grains and any additives together. The level of adhesion is critical because too much adhesion and the surface is hard and can't be levelled and harrowed, whilst too little adhesion and the footing is loose and unsupportive. Many of our competitors supply a coated surface in which the coating is a petroleum wax. Attwood's Pinnacle, Ameritrack and TerraNova footings are coated with a polymer, and in fact we believe Attwood is the only company supplying surfaces that incorporate a polymer coating. Our competitors use wax because it is a reasonably cheap by-product from the distillation of crude oil, and is fairly simple to apply. This is because the wax melts like a candle, and this is exploited to coat the sand more easily. However this melting is a severe disadvantage because in hotter weather the wax coating re-melts, turns into a liquid and the footing properties change significantly, with the surface losing cohesion and riding deep. The polymers used in Attwood's coating do not melt in this way and so properties do not significantly change with temperature. We discuss this aspect in detail later.
A significant theoretical advantage of coated surfaces is that they are dustfree. In other words, even in the driest of weather they should not generate dust.

Uncoated surfaces rely on water to bind the particles together. It may seem strange that water is used to 'glue' together sand and additive particles, but it really works if the correct sand, additives and amount of water are used. The adhesion mechanism is based on hydrogen bonding, a phenomenon chemists have known about for many years. Its effect on sand is dramatic. Consider the difference between dry sand in the dunes at the seaside, and that at the shoreline. The dry sand is free flowing whilst the wet sand is hard and compact. Any child soon learns that the sand needs to be wet to make sandcastles!

For both types of sand-based footing, coated and uncoated, various additives are usually blended. These are usually textile in nature, although rubber and plastic, and wood pieces are also used. The technical reason for adding an appropriate additive is to improve cohesion in the surface, and to improve impact resistance and rebound. However many of our competitors have a different reason - they use cheap, often recycled additives to reduce their costs. We discuss this in detail later.

Sand

The key to a good surface is the sand. Many footing manufacturers and installers consider all sands to be the same and simply choose the cheapest available, which can be disastrous. At Attwood we understand sand, & know how sand contributes to the properties of equestrian riding surfaces.

The Oxford English Dictionary describes sand as: "a loose granular substance, typically pale yellowish brown, resulting from the erosion of siliceous and other rocks and forming a major constituent of beaches, river beds, the seabed, and deserts." The key word here is siliceous which means silicon in origin, and in the case of sand refers to silicon dioxide, or silica. This is a very hard material that gives good quality sand its hardwearing properties. But notice also that sand can be derived from other rocks, and this is where lower quality sand comes in. A common alternative rock is calcium carbonate which is a significantly softer material than silica and will easily crush to form finer and finer particles.

Scientific measures of Absolute Hardness give a value of 100 to silica, whilst calcium carbonate has a value of only 9.

Typically, sand is a mixture of minerals, but the highest quality sand is composed mainly of silica - usually greater than 95%. Other minerals can give sand its colour such as iron oxide which yields a yellow/ brown colour.


A second characteristic of sand is the grain size distribution. Grains can vary in size from around 2mm, down to 0.063mm - particles smaller than this are classified as 'silt'. Particle size has a profound influence on footing properties.

For instance bigger grains tend to drain well because the spaces between them are large, and the route down through a layer of sand is less tortuous. However large grains can drain water so well that a footing will dry out too quickly and require excessive watering. Also clearly not all grains will be the same size and the spread of sizes also influences surface properties.

A third characteristic is the grain shape. A classification based on the visual appearance of grains under a microscope is used to describe average grain shape . Two attributes are checked, the sphericity, i.e. how round the grain is, and the angularity, i.e. how smooth the surface is.

The shape of the grains also has a large bearing on the way a footing behaves. This is because the grains rub against each other as the surface is compressed by the hoof, and so frictional properties are important in providing the correct level of support and cushioning.

At Attwood Equestrian Surfaces we are experts on sand, and only specify sand that will impart the desired properties and lifetime to a surface.

Additives

Additives include recycled tIre pieces, carpet pieces, wood chips, electrical cable insulation, woven and nonwoven felt/fabric, and a multitude of fibres. These materials are blended with sand to provide volume and add further cohesion/shear strength to the footing.

As we mentioned in the Types of Footing section, many footing manufacturers and suppliers do not understand the role additives play, and merely use the cheapest additive they can find to include as a cheap 'filler'. But additives serve a number of important purposes.

In uncoated sand-based surfaces, moisture is required to bind the sand grains together. In coated surfaces it is not moisture that bind grains together but the adhesive coating. However the strength of this binding between sand grains is not sufficient to give the footing the required level of cohesion to provide the necessary shear strength - the surface would not provide a stable enough footing for the horse. So materials should be included that increase the cohesion in the surface. Small fibres are particularly good at providing this cohesion, acting like a root structure in natural turf. Some footing manufacturers rely on the fibres from shredded carpet to 'knit' together the surface, but often the fibres are still bound to the carpet backing and are not free enough to do their job. Only if fibres are added in a loose form will they bind the footing together sufficiently. And non-fibrous additives like rubber impart very little, if any cohesion to the footing.

One important point on the economics of fibrous additives: be aware that additives are purchased by weight, e.g. by the ton. One additive might contain a lot of carpet backing, or plastic that offers no improvement to cohesion, and so contains much less of the valuable fibres needed for cohesion. Take a look at a range of commercially available fibrous additives in the pictures.

Firstly note how separated the fibres are. In the case of Additives 2 & 3, the fibre is in the form of carpet yarn where the individual fibres are designed to stay within the yarn tufts by twisting and setting - this is what you want from a carpet, but not what you want for footing!

Secondly, you'll have noticed that the amount of additive looks different. There is the same weight in each pile but because some contain heavy pieces of carpet backing or rubber, you get very little fibre for your money! In fact to get the same level of cohesion as Additive 1 from Additive 3, you would need approximately 4 times as much additive. So when you are considering which additive to buy for your arena, look at both the openness of the fibres, and the amount of fibre per weight of additive - it could be that the additive is full of cheap filler.

One final point on fibres is that the type, size and form of the fibre is important. Through years of research we have found that polyester fibre is a good choice because it is one of the most durable fibres known, helps to maintain moisture in an uncoated footing, and is compatible with the types of coatings used in coated footings. Fibres are manufactured in a range of diameters, known as denier (think tights or stockings), and can be used in a variety of individual fibre lengths.

We have determined the correct diameter and length of fibre for optimum performance in a surface. The graph shows how footing shear strength changes with the fibre length used in our coated surface, Pinnacle. Knowing which length to use is important, otherwise the footing might not be supportive enough, or conversely it could be too cohesive

A second role played by additives is to help provide shock absorption characteristics to the footing. Plain dry sand provides negligible shock absorption (see caption). Sand bound with either moisture or a coating has a little more, but not enough to sufficiently reduce the concussion experienced by a horse. The inclusion of additives increases the volume of the surface by introducing air spaces into the footing. These spaces collapse when the weight of the horse presses down on the surface, rather like squashing a foam.

The ease with which the structure collapses determines how supportive the surface feels, and this is determined partly by the nature and amount of additive. Fibres are particularly good at introducing the correct amount and size of spaces into the footing, and if blended correctly provide the same response over every square centimetre of the surface. Footing that has pieces of tyre scrap or carpet as additives can have reasonable shock absorption, but this can vary across the surface depending on whether or not the hoof happens to land on a piece of rubber or carpet.


We conclude this section on additives with some comment on their safety profile and environmental friendliness. Many additives available today are based on recycled materials. Whilst it may seem a noble gesture to purchase additive that is made from recycled materials, the customer needs to know exactly where the material came from and what is lurking within the material. In many cases it is preferable to use additives that are not from a recycled source so that the exact nature of the material is known and understood.

Recycled rubber pieces, particular from recycled tyres is a popular additive for equestrian surfaces because it offers a cheap method of imparting some shock absorption and rebound properties to the surface. However there is the possibility of some disturbing chemicals lurking within the rubber pieces. Worst of these are polyaromatic hydrocarbons (PAHs) which are added in the form of oils to soften the rubber, and comprise between 25% and 35% of the rubber.

These types of compound have been proven to be carcinogenic, teratogenic (affecting unborn foetus) and bioaccumulating. Even more disturbing, a report produced by Environmental and Human Health Inc., in 2007 found carcinogenic chemicals were emitted into the air and leached into groundwater from recycled rubber sports surfaces. The danger has been partially addressed by the EU which mandated in 2010 reduced levels of certain hazardous oils used by tyre manufactures in the EU. However, in a random audit of tyres sold in 2012, some 10% of tyres were found not to comply with the reduced levels, and the majority of these were imported from outside the EU.

Apart from these extremely dangerous PAHs, tyres also contain toxic phthalates (more on these later), and metals.

The disposal of used tyres is an enormous problem facing the developed world. There is reckoned to be 1 - 2 billion illegally stockpiled scrap tyres in the U.S.A. and a similar number in Europe. Because of their toxic nature, their disposal in landfill was banned in the EU in 2006. Controlled burning of tyres for energy recovery is possible but the plant and equipment to treat the toxic gases is incredibly expensive. This means that there is governmental pressure to find uses for scrap tyres, so legislation banning unsafe tyre re-use is non-existent.

PVC cable insulation scrap is another popular additive in equestrian riding surfaces. This provides a small amount of shock absorbency, but confers no cohesion to the footing. Here too there are health, safety and environmental concerns because of the plasticisers in PVC . These are chemicals called phthalates which in recent years have been shown to be hazardous to health, so the EU and United States are beginning to ban the use of certain phthalates used for many years in cable insulation, although progress is slow. Probably the most popular additive based on recycled material is carpet scrap. The danger here is less environmental but more health and safety. Many suppliers sell post consumer carpet scrap, that is shredded carpet that has previously been installed in homes or in 'industrial' settings. Two easily identifiable hazards exist. One is that often this carpet is not cleaned before being shredded so still contains unknown 'soil' from its many years of use. Secondly, although the supplier will insist the product contains no metal particles, there is still the possibility for carpet tacks, gripper tacks etc. to survive the collection and shredding process, and end up in your arena.

Coated, dust-free surfaces

Response to temperature changes:

Top-end synthetic equestrian surfaces are coated products that are claimed to require no watering and are dust-free. These products are virtually all based on using wax as a coating. Attwood's coated footings, Pinnacle, Ameritrack and TerraNova are not coated with wax but use a polymer coating, but more on this later. The wax substance is used by our competitors because it is able to coat the sand grains and any additive particles/fibres with a sticky coating to bind all the components together to give the surface cohesion.

However, waxes used in these footings are crystalline by nature and hence have a melting point (think of candle wax and how it turns to liquid when it melts). Imagine what happens to the footing properties when the wax melts! The adhesive polymers used by Attwood for its Pinnacle, Ameritrack and TerraNova footings have a very low level of crystallinity so do not turn to liquid when heated. We can monitor the amount of melting in a material by a method called Differential Scanning Calorimetry.

The graph shows a wax as it is heated from 0°C to 120°C and the brown curve is the energy absorbed when the material melts - the size, or strictly the area under the peak is a measure of how strongly the material melts i.e. how much it turns to liquid. For wax the area is typically around 200 J/g. The tan line shows Attwood's polymer trace superimposed - the area is around 8 J/g. Because there is such a weak melting effect, the Attwood polymer does not turn to liquid when it is heated.

This means that wax-based surfaces change quite dramatically with changes in temperature, not just through the seasons but within a single day.

We naturally think that the temperature an equestrian surface reaches over a typical year for a given climate matches the published temperature given for the 'weather' in our region. However this would be incorrect and would grossly underestimate the temperature range the surface will be subjected to. This is especially true at the high temperatures encountered during summer. This is because official temperatures given by the weather media are air temperatures, measured out of direct sunlight, usually in a special cabinet. Because of the effect of direct sunlight, the temperature of a surface will be higher than the air temperature, sometimes dramatically higher. But it is more complicated than this because the surface temperature will also depend on the colour of that surface, and also to a certain extent its surface roughness but we won't consider that here.

Most people know that darker surfaces get hotter when exposed to sunlight, but perhaps not many know just how much hotter.

For instance the surface temperature of the bodywork of a black car can be as much as 30°C hotter than a white car. So imagine your equestrian surface on a sunny day in a temperate climate, with the outside temperature at 25°C, the footing temperature could be as high as 55°C.

The highest natural surface temperature recorded was in the Lut Desert in Iran in 2005, registering 70.6°C!

Now think about your arena in winter, with sub-zero temperatures. During prolonged cold weather the surface temperature is likely to be at the actual sub-zero air temperature. In hot weather a waxed surface can become loose and ride deep, whilst in cold weather it can become hard and brittle. In contrast, Attwood's Pinnacle, Ameritrack and TerraNova footing products are manufactured without wax, and therefore are more stable in extreme temperature conditions.


The graph demonstrates this by showing how footing shear strength ('tightness') changes with temperature for wax and Pinnacle footings. Whilst the Pinnacle always remains within the acceptable shear strength range, the wax-based footing falls outside the range at higher and lower temperatures.

Several manufacturers supplying wax-based synthetic surfaces will boast of the number of arena and racetrack installations they have completed, but none will tell of the problems associated with variability of surface properties with temperature, and the number of high profile installations that have since removed their surface.

Lifetime:

Dust-free coated surfaces such as waxed surfaces can become ineffective whereby the coating wears off and the surface loses cohesion and 'rides deep'. In poor quality surfaces this can happen as quickly as 2 - 3 years after installation. Attwood has developed a laboratory test that reproduces the type of wear a surface will endure during its life, but which takes only several hours to complete, rather than waiting years for a result.

The captions show a commercial wax surface before and after the test, along with Attwood's Pinnacle footing. The polymer-coated Pinnacle and has a far more robust coating and can last up to 5 times longer than a typical wax surface. Indeed we have many customers whose surface is still going strong ten, even fifteen years later.

It is easy to see when a coated surface is getting tired or has worn out. In this case the surface will lack cohesion and the ride will be deep. This is because the 'sticky' coating has partly, or completely worn off, leaving nothing to bind the grains and fiber/additive together.

In cases we encounter like this, the customer will be watering their surface just to maintain some level of cohesion - this for a surface that is sold on its non-watering advantages! Indeed we come across waxed surface customers who are having to do this as little as three years from the installation date. Attwood's coated product, Pinnacle, uses a polymer coating which binds to the sand and additive in a far stronger way than a wax, leading to wear life up to 5 times longer than wax surfaces.

Tired wax coated surfaces can usually be re-waxed, but we seldom come across re-waxed surfaces that return to their original properties. Attwood too can re-coat a tired surface, but we use a superior polymer coating. Indeed in some cases we can re-coat a tired waxed surface, but compatibility has to be ascertained first.

Uncoated (watered) footing

As we described earlier, an uncoated footing requires water within the surface to operate properly. Too little and the footing lacks cohesion and will ride deep, too much and the footing will become sloppy and also loose cohesion and support. Simple sand surfaces containing no additives are not a safe solution since there is very little shock absorption inherent in the surface. Additives help to create the volume necessary for the absorption of energy when the hoof strikes the surface. In the Additives section earlier we described the various additives that are used in the industry. Attwood's own Eurotex additive is a fibre felt mix that provides both cohesion and shock absorbency. The Eurotex surface requires moisture within the footing to perform in an optimum manner and we have scientifically determined what that level should be to give the best performance. The graph illustrates how the shock absorption varies with moisture content of the footing. Acceptable shock absorption is achieved over a range of moisture contents, and it is this range that we tell our customers to target.

The Eurotex additive serves two other useful purposes. Firstly the moisture content range over which shock absorption is in the acceptable window is extended when Eurotex footing is used. This means that it is less critical to control moisture content. In addition the presence of the additive reduces the water loss rate, giving a much longer lasting moist footing, and increasing intervals between watering.


Measuring the Properties & Characteristics of Equestrian Surfaces

When you buy an expensive item, such as a car, some measurement of the performance of the car for instance in the form of top speed, mileage per gallon, or emissions has been carried out.

In some cases a particular measurement might be a regulated measurement, such that the property it measures can be said to perform to a particular standard.

Why is it then that with such an expensive product as equestrian footing, there are no accepted standards covering the performance of equestrian surfaces? Worse still, the majority of surface suppliers offer no standards or measurements on their products.

In our experience neither do they use measurements when they install surfaces to ensure the footing has been manufactured correctly and installed correctly.

Indeed even at the highest competition levels there are no accepted standards, and the surface at one event can be very different from the next. The Federation Equestre Internationale (FEI) , the governing body for Equestrian Sport has recognised this problem and has initiated research aimed at defining what the standards should be and reproducible ways of measuring surface properties.

A white paper partly funded by the F.E.I was published in April 2014 which provides background knowledge on the interaction between horse and surface, with a view to subsequently devising standards for equestrian surfaces. In it, 5 parameters were identified as important measures of a surface, around which standards could be developed. The parameters Impact Firmness, Cushioning, Responsiveness, Grip and Uniformity together describe the important features of a surface in relation to horse and rider engaged in equestrian sport.

The first three parameters relate to the impact of the hoof on the surface and its subsequent lifting ready for the next stride. Most will have noticed the difference in impact between a very firm surface such a tarmac road, and a very soft surface such as loose sand. The response of the hoof to each of these is quite different.

Clearly the fourth parameter, grip, will relate to cornering, stopping and accelerating. The final parameter, Uniformity, speaks for itself. Ultimately these parameters will need to be measured and will have to fall within certain values in order for a surface to be considered FEI acceptable.

Here at Attwood we have always recognised that objective measurements of the properties of equestrian surfaces are required rather than simply relying on the subjective feel of the surface. You can see from the sections above that we have made many measurements on the different components and footings available. Because no equipment is commercially available to measure these parameters, we have developed tests and equipment to measure key properties, such as those listed in the F.E.I. white paper. The methods and equipment used to measure these properties are so valuable to us that we don't share them externally as we feel they give us a significant edge over our competitors. We use these measurements both in quality control when we manufacture and install our surfaces, and when developing new and improved surfaces.

Of course there are, what can be described as 'second level' parameters that are not direct measures of the final surface, but measurements of the properties of the components that make up an equestrian surface. Such a second level measurement might be the grain size distribution of the sand. This parameter is usually measured by a sieve analysis where the sand is shaken through a stack of sieves of gradually decreasing size and weighing the amount of sand retained by each sieve.

The largest grains are retained on the sieve with the largest holes whilst the smaller grains can fall through these to be retained on the sieves below with smaller holes. This grain size distribution is very important in partly defining the final properties of the surface. Another is the amount of additive such as fibre or fabric/felt incorporated into the sand, and this can be measured by separating the sand from the additive and weighing the two fractions.

How many of the suppliers you have dealings with measure even these basic parameters let alone the complicated parameters such as Impact Firmness and Cushioning? We routinely meet customers with failed surfaces who tell us the supplier used no measurements at all, either during manufacture or post installation.