Understanding Footing Materials

Courtesy of PennState Extension

The primary principle of selecting footing materials is to obtain materials that maintain their loose nature without compaction while providing stability for riding or driving activity. The major component of most footing is a mixture of naturally occurring sand, silt, and clay particles.

Sand

Sand is the common ingredient in many arena surfaces and ranges from fine sand at 0.05 mm diameter to coarse sand at 2.00 mm diameter. Sand alone may be used but it is often combined with other particle sizes or other materials. Be careful to apply the proper depth of sand. With its deep, loose traction, sand deeper than 6 inches is stressful to horse tendons. Start with about 2 inches and add a ½ inch at a time as necessary. (Start with only 1½ inches for arenas used primarily for driving horses.) Newly laid sand contains air pockets that absorb shock and rebounds. However, despite its solid, inorganic nature, sand will erode and compact into an unsuitable surface over time.

Sand dries out fairly rapidly since it drains well, so frequent watering is essential. Some managers add a water-holding material, such as a wood product or commercial additive, to the sand footing material to hold water between watering events, hence reducing dust.

Certain specifications of sand are required for good footing material. Riding arena surfaces should contain cleaned and screened, medium to coarse, hard, sharp sand. Fine sand will break down more readily into small enough particles to be lofted as dust. “Cleaned” means the material has been washed of silt and clay, making the sand less compactable and less dusty. “Screened” means large, undesirable particles have been removed and a more uniform-sized material remains that will be less prone to compaction. “Hard” is quartz sand, which will last up to 10 years. Obtained from a quarry, sub-angular sand has sharp particles, versus the rounded particles found in river sand. The sub-angular particles of naturally occurring, mined materials are old deposits of sand that have weathered from natural forces of water (typically) into particles that are still angular for stability as an arena surface. Manufactured sand is very fine, crushed rock and is also angular, but not as hard as real sand. Angular sand provides better stability than rounded sand particles, which behave similar to millions of ball bearings underfoot.

Sand is often one of the cheapest materials to use for arena footing material, yet the hard, angular, washed sand that is most suitable as a riding surface is among the most expensive sands. “Waste” or “dead” sand contains considerable quantities of the silt and clay particles that are the by-product of “clean” sand and is unacceptable for good arena footing. Cleaned, washed sand alone is too loose for some riding disciplines that require sharp turns and stops, such as barrel racing and cutting. Wetted sand provides much more traction than dry sand, but frequent and abundant watering is needed and this is not realistic in some locations.

Allowing 5 to 10 percent fines (passing through a number 200 screen, which has 0.075 millimeter hole size) in the chosen sand product provides particles that help bind the larger sand particles. More fines than this will cause the sand mixture to become very dusty and slippery when wet. Providing 5 percent fines will allow some binding activity while decreasing dust potential; as the sand wears, the fine particle percentage will increase. For those arena surfaces designed to use native topsoil, 10 to 30 percent of the mixture may be “dirt” with the balance sand.

Unfortunately, the fines in either of these mixtures will loft as dust if not managed for dust suppression. Fibers, natural or synthetic, may be used to bind loose sand with less risk of adding dustiness but of greater cost than the addition of fines or local soil. A combination sand-soil arena is popular with western riding events where high stability is needed for speed events so the footing can be kept moist and more compacted or harrowed into a loose mixture for sliding stops and cutting work.

Other materials, such as wood and rubber, may be mixed with sand to overcome some difficulty encountered when using sand alone. Wood products added to sand footings will add moisture-holding capacity and improve traction while adding some cushioning. Rubber adds cushion to a sand footing and can prolong the useful life of the sand through decreased abrasion of sand particles on sand particles. While rubber can add some cushion to worn sand footing, for old, eroded sand the better long-term fix is to discard the failed surface material and replace with a new mixture. Rubber is a relatively expensive addition to a footing that has outlived its useful life and is best replaced.

Wood Products

These may be used as the primary footing material or mixed with other footing materials. Wood chips or coarse sawdust will provide some cushioning and moisture-holding capacity to an all-inorganic footing (sand, stonedust). Wood products are quite variable, not only from location to location around the country, but even from load to load at the same wood mill. Any wood product will eventually decompose since it is organic, and smaller and softer wood products will break down into smaller particles that will eventually lead to compacted footing. Expect to add more wood product every couple of years as the older wood decomposes. Eventually, some footing may have to be removed to maintain an appropriate depth.

Manufactured wood products may be used as the predominant footing component. All-wood footing offers cushioning in a material with fibers that interlace for traction. Wood footing materials contain pieces that are larger and more durable than wood chips or sawdust and require little maintenance when installed correctly. Wood footing has ½- to 1-inch slender pieces, or wood “fiber” mixed with some finer wood for knitting the wood footing to the base material. All-wood footing is often installed on a 1-inch layer of wetted, washed, angular sand to further tie the wood pieces into the highly compacted base surface. Hardwood pieces will last longer than softwood products. Do NOT use walnut and black cherry hardwood products as they are highly toxic to horses. For this reason and for quality control in eliminating contaminants in the shipment (large wood chunks, nails, staples from ground pallets, etc.), buying wood footing from a manufacturer that specializes in supplying horse arena footing is recommended. An advantage of all-wood footing is the reduced abrasiveness on horse hooves compared to sand- and stonedust-based footing materials. The material must be kept moist to maintain adhesiveness of the wood pieces with each other. Fully dried all-wood footing can become slippery as the wood becomes more brittle and does not as effectively interlace for stability. In contrast, all-wood footing with large pieces (for example, chunk bark or wood greater than 1 square inch, not slender) becomes slippery when overly wet.

Rubber

Rubber from recycled shoes or Rubber tires can be ground or shredded into small particles. Rubber source may vary so use products from a horse footing material supplier. Be sure to get a guarantee that the shredded product will not contain metal (from steel-belted tires) or other foreign materials or thoroughly check the load upon delivery. Ground rubber is usually mixed with sand or other surface material to minimize compaction and add some cushion into the surface. Rubber product won’t degrade like wood but will break down into smaller pieces through grinding against sand and horse hooves. Its ability to darken an outdoor arena surface color reduces glare and helps thaw the surface faster during winter by absorbing more solar radiation. Pure rubber tends to be too bouncy and the black color provides significant heat on outdoor arena users. Indoor arena users may notice the rubber odor. Most horses are not prone to eat it should they have free access to the arena footing. Rubber pieces float and with heavy rainfall can separate out of the footing material mixture (Figure 2). Simply reincorporate with surface conditioning equipment. Rubber is added to a sand or stonedust footing at the rate of 1 to 2 pounds of rubber per square foot. Crumb-shaped rubber pieces are suitable to reduce compaction in a sand-dirt or stonedust mixture. Flat rubber pieces (or fibers) will help knit together an all-sand, clean footing that needs more stability. The rubber fibers essentially knit together the entire depth of footing profile to create a material that does not shift as readily as pure sand.

Stonedust

Stonedust remains in the “common” footing material category but may really belong in the “challenging” category due the high level of management needed to maintain suitable arena conditions. Stonedust provides good stability, drains well, and can be an attractive surface if kept watered and harrowed. It can be a very suitable footing material when kept damp. It will be almost as hard as concrete if allowed to compact and dry. Stonedust is extremely dusty if not kept constantly moist throughout the entire depth of footing. Stonedust is a very cheap material, which enhances its attractiveness, but frequent, diligent management will be needed to control dust in an indoor arena environment or for outdoor arenas outside of the rainy season.

For footing material, the stonedust (also known as blue stone, rockdust, limestone screenings, decomposed granite, or white stone) should contain a narrow range of grade sizes so that it does not compact easily. Stonedust is a finer version of the road base material used in arena base preparation. If the stonedust in your area is well graded and is suitable as a compacted base material, it will be difficult to keep loose as a footing material. In contrast, when stonedust is not compactable, it can make a suitable arena footing material.

Stonedust mixed with rubber will provide a less compactable footing than stonedust alone while keeping the high-stability stonedust offers for quick changes in direction and speeds, such as jump takeoff and landing activity.