Silica sand for equestrian surfaces: particle size, moisture, dust and qualification

Sand for an equestrian surface cannot be qualified only by its SiO₂ content. In a riding arena, the response experienced by the horse comes from a complete system: particle-size distribution, grain shape, fines, moisture, possible additives, depth, drainage, base and maintenance [1–3].

The FEI identifies five functional properties of an arena surface: impact firmness, cushioning, responsiveness, grip and uniformity. In other words, good sand is not merely “clean” or “hard”: it needs to contribute to a surface that is sufficiently stable, cushioning, responsive, grippy and consistent for the intended use [2].

Key takeaway: the right purchase is not simply “0/x sand” or “high-silica sand”. It is a material whose properties remain compatible with the surface system, discipline, climate and maintenance programme.

1. Why should particle size be described as a curve rather than one nominal range?

FEI guidance highlights three essential parameters for characterising sand: grain shape, size and sorting [1].

A commercial description such as “0–2 mm” only gives nominal bounds. It does not show how mass is actually distributed among the different sizes. Two sands carrying the same label can therefore have:

• very different fine fractions;
• different central grading;
• different pore sizes;
• different compaction tendencies;
• different responses to water and additives.

The FEI also recalls the general particle-size classification in which sand lies between 0.063 and 2 mm, while smaller fractions are classified as silt and clay. This is a particle-size classification, not an equestrian-footing specification [1].

For the buyer, the useful document is therefore a complete sieve analysis, with the test method and the fraction below 0.063 mm clearly identified.

2. Grain shape: stability, compaction and wear are connected

Grain shape affects how particles interlock and move under the hoof.

FEI guidance distinguishes natural grains, which are often rounded or subrounded, from crushed materials that are usually more angular when new [1].

Greater angularity can improve interlocking and stability. But it is not automatically preferable: sharp edges can wear, gradually generate more fines and change the particle-size distribution over time.

Conversely, very round and highly uniform grains can create a mobile surface, similar to balls rolling against one another. Their behaviour can nevertheless be modified by a broader grading or by fibres and binders [1].

The more useful supplier question is therefore:

which combination of shape + grading + additive + moisture produces the functional response required?

3. Fines, silt and clay: neither always bad nor freely interchangeable

The fraction below 0.063 mm deserves separate attention.

FEI guidance explains that this fraction may contain silt, clay, mineral fines or particles generated by wear. Behaviour does not depend only on size: some clays have morphology and activity that can strongly modify cohesion and water retention [1].

A small amount of fines can contribute to particle binding. Excessive fines can instead:

• increase compaction;
• reduce pore space;
• slow drainage;
• increase moisture sensitivity;
• increase dust when dry;
• progressively clog some drainage structures.

FEI guidance reports different practices and percentages used by consultants and commercial producers, but these figures are not a universal specification [1].

To compare two materials, it is more robust to request:

1. percentage below 0.063 mm;
2. nature of that fraction where significant;
3. test method;
4. change in the fine fraction after wear;
5. the intended role of fines in the final system.

4. “Washed sand”: useful information, but not enough

Washing can reduce silt, clay and fine contamination. That can make the raw material easier to control.

But “washed” does not automatically mean “ideal for horses”.

FEI guidance notes that washed sand used on its own can become too loose if the grains are too uniform and the fractions that previously contributed cohesion have been removed [1].

Washing should therefore be read as a processing step, not as a final performance claim.

A specification should instead combine:

• particle-size curve;
• fines content;
• grain shape;
• mineralogy;
• delivery moisture;
• response with additives;
• durability under use.

5. Why is moisture a central variable?

The FEI White Paper describes moisture as one of the most important variables controlling the consistency and functional properties of sand-based surfaces [3].

Water changes forces between particles. It can influence:

• shear strength;
• compaction;
• hoof penetration;
• lateral stability;
• dust;
• footing response after harrowing.

But more water is not always better. As the material approaches saturation, its behaviour changes again. The optimum moisture depends on surface type and discipline [3].

A 2019 study of 25 indoor arenas judged by their managers to have good rideability measured different mean moisture contents by surface family, broadly within about 9 to 15% across the three categories studied [4].

That range is useful as an experimental observation, but it should not become a universal purchasing specification: the materials included pure sand, sand with wood chips and sand with fibre, with different densities and formulations.

6. Dust: a material, moisture and operation issue

Dry footing can release more airborne particles during riding.

A longitudinal study in four indoor arenas found that particle numbers increased after a riding session and varied with arena, month, activity and likely watering practices [5].

The 2019 study of 25 surfaces also found large differences in PM10 release between and within footing families. Sand-fibre surfaces had a higher average release in that experiment, with substantial variation driven by particular samples [4].

Two important conclusions follow:

• the commercial material alone does not predict real dust exposure;
• watering, harrowing, ventilation, surface age and segregation of components also matter.

For a buyer, a simple “dust free” claim should therefore be treated cautiously unless it is accompanied by a test method and operating conditions.

7. Quartz-rich sand and respirable crystalline silica: do not confuse composition with exposure

Silica sand can contain a high proportion of crystalline quartz.

NIOSH explains that respirable crystalline silica is the fraction of crystalline-silica-containing particles small enough to penetrate deep into the lungs and that excessive exposure can cause serious respiratory disease [7].

In an equestrian surface, this does not mean that a quartz percentage on the CoA automatically equals an airborne exposure concentration.

The following should be separated:

• sand mineralogy;
• amount of fines and dust generated;
• actual respirable fraction;
• frequency and intensity of arena use;
• moisture and ventilation;
• occupational-health rules applying in the relevant country.

For an international project, a prudent approach is to document mineralogy where needed, control dust generation, and leave formal exposure assessment to the responsible site operator under the applicable jurisdiction.

For the difference between bulk chemistry and mineralogy, see our guide to XRF and XRD analysis of silica sand.

8. Fibre, wood and wax: the sand needs to fit the system

Many modern equestrian surfaces combine sand with textile fibres, wood chips, polymers or wax.

These additives may modify:

• cohesion;
• elasticity;
• recovery after impact;
• turning stability;
• compaction;
• moisture sensitivity.

FEI guidance explains that sand selection for fibre systems should be considered together with the additive. A grading that works for a simple sand arena will not necessarily perform the same way with fibre or wax [1,3].

This is why copying another facility’s recipe can fail: the local sand, additive, base, water and maintenance may all differ.

9. The five FEI functional properties: what the buyer should preserve

The FEI Standard for Arena Surfaces identifies five measurable functional properties [2]:

Property	Practical interpretation
Impact firmness	Initial ground response at hoof contact
Cushioning	Ability to absorb and distribute part of the load
Responsiveness	Energy return / elastic response after loading
Grip	Resistance to sliding and shearing
Uniformity	Consistency of these properties across space and time

These are not properties of raw sand alone. They emerge from the built and maintained system.

The sand supplier contributes through grading, shape, durability, fines and lot consistency. The installer and operator then control depth, water, levelling, harrowing, base and drainage.

10. Sand durability matters because footing changes over time

An arena is not static.

Hoof action, harrowing and equipment can wear and fracture grains. The fine fraction can increase, progressively changing compaction, drainage and dust.

FEI guidance cites silica sand as an example of a durable material in certain systems, particularly where resistance to crushing and wear helps preserve particle-size structure [1].

But “silica” alone does not guarantee this durability. Mineralogy, grain defects, shape, processing and loading conditions also matter.

Supplier qualification should therefore consider not only initial condition, but also how well the material is likely to remain stable through use.

11. Maintenance can change performance faster than the raw material

The Frontiers study of 656 equestrian surfaces in Sweden shows that watering and maintenance strongly affect footing properties and that maintenance frequency varies widely between facilities [6].

The same raw material can therefore perform very differently depending on:

• watering frequency;
• uniformity of water application;
• type and depth of harrowing;
• horse traffic;
• indoor or outdoor climate;
• levelling frequency;
• depth control.

For the buyer, an important distinction follows:

supplier specification ≠ operating protocol.

They must be compatible, but they should not be collapsed into one particle-size number.

12. What should the sand supplier dossier contain?

A useful dossier can include:

Control	Why it matters
Full particle-size curve	Shows actual distribution, not only nominal bounds
Fraction <0.063 mm	Tracks silt, clay and fines
Shape / angularity	Helps anticipate interlocking, mobility and compaction
Mineralogy	Documents quartz and other phases where relevant
Delivery moisture	Supports consistent lot comparison
Bulk density	Helps sizing and material monitoring
Wear / durability test when required	Helps assess future fines generation
Representative sample	Supports pilot testing
Lot number and CoA	Links analysis to delivery
Inter-lot tolerances	Maintains system consistency over time

For quartz-rich material, chemical analysis alone does not replace mineralogy. See also our general silica sand guide.

13. A nine-step qualification procedure

To reduce the risk of a poor selection:

1. define the discipline and use intensity;
2. describe base, drainage and indoor/outdoor environment;
3. select several logistically available sands;
4. compare grading, shape and fines;
5. verify mineralogy where it affects durability or dust;
6. test the sand with the planned additives;
7. build a pilot area at full working depth;
8. adjust watering and maintenance over several use cycles;
9. only then set the supplier specification and lot tolerances.

This avoids ordering an industrial volume from one dry sample or a commercial data sheet alone.

Conclusion

For equestrian surfaces, sand is a component of the system, not the system itself.

Particle-size distribution, grain shape, fines and durability need to be qualified together with moisture, additives, construction and the maintenance plan. Indoor-arena studies also show that dust and moisture can vary substantially even among surfaces considered rideable.

A robust specification therefore combines raw-material characterisation + system trial + maintenance protocol + lot control. That coherence, more than one isolated SiO₂ percentage or nominal sieve range, reduces the risk of footing that becomes unstable, dusty or difficult to maintain.

References

1. Fédération Equestre Internationale, Equestrian Surfaces - A Guide.
2. Fédération Equestre Internationale, FEI Standard for Arena Surfaces.
3. Hobbs et al., Equine Surfaces White Paper, FEI.
4. Claußen, Grau & Hessel, Journal of Equine Veterinary Science, 2019.
5. Lühe et al., Equine Veterinary Journal, 2017.
6. Frontiers in Veterinary Science, study of 656 equestrian sport surfaces in Sweden, 2021.
7. NIOSH, Silica and Worker Health, 2026.