Question: I’ve kept my horses in two dry lots for 15 years. Now it’s time to raise the area up anywhere from six to 10 inches. To save on costs, I’m considering using slag from a nearby metal/steel refinery as a base. I’m wondering whether it will be safe for the horses, the groundwater and the environment. Can you help? Have you heard of anyone using slag for any horse application?
Answer: For those of you who did not grow up in steel-making regions, as I did, slag is the leftover material after a desirable metal is separated (smelted) at high temperatures from its ore. Specifically, steel slag is a nonmetallic product developed simultaneously within steel furnaces. Around steel mills, small mountains of the stuff are a common sight.
So slag is a very hard, rock-like material that is in abundant supply—and thus relatively inexpensive—near steel and other metal refineries. Fortunately, there is a professional group of people well versed in how to repurpose slag for construction and agricultural uses: the National Slag Association (NSA). According to the NSA, slag has been used in road building for about 2,000 years. And that gives the first indication that this material has properties useful for improving a dry lot corral for horses.
I have heard of slag being used successfully as a base in riding arenas and cattle yards, because it compacts well and is durable. So considering using slag as a base for a dry lot paddock seems warranted.
Basically, building a dry lot paddock is like laying down a road for cars, in terms of the compaction of construction layers and drainage issues. The difference is that the paddock is topped with material suitable for equine hooves rather than asphalt or concrete. Road base mix is well suited for use in constructing the “base” of equine dry lots and riding arenas. This material is composed of a range of particle sizes that allow compaction by finer material filling gaps between larger particles to provide the stability needed in a base. For building or improving paddock dry lots, I recommend a solid, stable base of highly-compacted road base aggregate topped with a softer, fine material to fill any harsh surface characteristics.
If you’re considering using slag on your horse farm, I would make three recommendations:
• Choose the right product. Not all slags are the same. The key is to source only iron or steel slag to get an environmentally suitable product. Look for slag with a low expansion rate to reduce swelling upon wetting and processed to exclude tiny metal fragments.
• Select the right particle sizes. Use a larger size ballast of one-inch particles as a thick base to stabilize a muddy high-traffic area; fines must then be added to the surface to fill or “choke off” the surface roughness. Slag is very hard and its shape is irregular angular—properties that provide excellent site stability and durability. But slag base ballast must have a fine material on top capable of smoothing the rough hard surface for comfort. Fines can be “ag-lime” slag, which is processed to meet environmental metal composition thresholds for land application in agriculture soils. I recommend smoothing the surface further by taking the additional step of adding an inch or two of organic material, such as compost, that works into the surface to soften it further for horses.
• Find a reputable contractor. You want someone who knows slag products and is experienced in installing them for use with horses. Costs of construction or renovation include not only the raw material, slag in this case, but site preparation then delivery and installation of the dry lot base material. Be wary of cutting corners on any one aspect to the detriment of the whole project.
Overall, properly chosen slag is an environmentally responsible option that recycles an inexpensive industrial byproduct for use as the base of dry lot paddocks. But it’s essential to top the rough slag surface with fine material that ensures the comfort of the horses in the paddock.
Eileen Fabian-Wheeler, PhD
Pennsylvania State University
University Park, Pennsylvania
Eileen Fabian-Wheeler, PhD, is a professor of agricultural engineering at Penn State University and a lifelong horse enthusiast. Her research and outreach efforts focus on environmental biophysics within agricultural structures. Priority areas include impact of environment on animal welfare and plant production, ventilation system performance, and reduction of air emissions.
This article was originally published the February 2016 issue, Volume #473 of EQUUS magazine
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