Put it to Use
• Find out what type of soil you're dealing with.
• A sub-base may be skipped, but not a base.
• Sand is economical.
• Adjust footing depth to your discipline.
Materials
Once you have settled the larger design issues, you can focus on your materials. Which material is locally available affects your base choices. Bluestone, for example, is a common base on the East Coast. But it's not native to many Western areas and so would be prohibitively expensive. Texans use crushed limestone, crushed concrete, or decomposed granite for a base. Floridians till sludge into the native sugar sand, level it, let it cure for a month or more, and then put the footing on top. Whichever stonedust base material you choose to use, make sure the quarry knows that you want it all to be of one grade size so that it does not compact and harden too easily.
The base needs to be level--unless you are sloping or crowning your arena--and packed. It should be compact in order not to shift around under the footing. The base is also non-absorbent: You want excess rainwater to run off the sides of the surface and in to the drain, not trickle down to the base. Although jumping arenas need a base of anywhere from 7" to 12" because of how hard horses land on it, dressage arenas can get by with about 4" to 6".
Costs
Trying to keep costs down, Foulk put in an arena in New Jersey. She found a level spot and removed the topsoil. For a base, she used crushed bluestone from a quarry. To save on hiring a roller, she compacted the base with farm vehicles and riding. Now, however, she considers the riding a mistake, and blames the unrolled bluestone for some hock problems her mare suffered. (Another way to avoid paying for a roller is simply to let the base sit over the winter, and let it compact on its own through exposure to the elements.)
Sand is the most common--and often cheapest surface footing for an arena. "Cleaned and screened" sand is nice for arenas, because it is both less dusty and less likely to compact. But it's also more expensive, so your best bet to keep costs down is to blend some rubber in with your lower-grade-also called "straight"-sand.
You will need to get rubber from a riding-arena footing company. (And don't use rubber if you've got a latex allergy, because it will enter the air around the arena and cause a reaction.)
The U.S. Dressage Federation's 2000 brochure on arena construction, "Under Foot," gives this useful sand calculation: arena length x arena width x desired depth of sand/324 = cubic yards of sand needed. For the tonnage of sand you'll need, multiply this number by 1.3. You can always add more, but it's hard and costly to have sand removed. Start with 1 1/2 inches, and go from there if you need more. Overly deep sand feels cushy for the first couple of steps, but it's hard on your horse's joints when he's working.
Keep sand costs down by comparison shopping, and possibly hiring the delivery service used by the sandlot rather than having your contractor pick it up. Besides the obvious sand-and-gravel services, many nurseries, quarries, and landscaping companies sell sand.
Although not necessary, railroad ties or other barriers work to keep the arena demarcated and prevent your footing from spreading. Many horses respond better to some kind of perimeter fence, no matter how low.
You need to allow for drainage under the ties, or your arena will pond when it rains. Railroad ties can be staked with retaining bars-metal dowel-shaped bars that are drilled into the tie-so that the ties are not resting directly on the ground.
Bottom Line
You need a safe, flat spot to school your horse, but costs can be prohibitive when it comes to designer footing and fancy fencing. Stick with what's available in your area, but don't skip the base and be certain you have adequate slope for drainage. And give strong consideration to a perimeter.
