(first appeared in the April 2015 issue of The Equiery)
1. Using the wrong quality or quantity of stone
Quality: Be aware of the type of materials required versus what is being supplied. For the base layer (stone drainage layer), clean, hard, angular stone must be used. What does this mean?
“Clean” means the stone has been washed so stone dust/fine soil is not washed straight into your drains, causing reduced flow of surplus water.
“Hard” means the stones are frost resistant, i.e., will not break down after successive winters, or fracture due to the weight of maintenance machinery. Granite or a hard limestone (not soft limestone) are is usually preferred. Take two stones and bang them together; they should not dust, crack or break. If they do, they are not frost resistant. If in doubt, the quarry can provide a technical data sheet.
“Angular” means stones that can interlink together, so they need to be of similar size, typically 1 3/4’’ to 2 3/4’’. If the stone is rounded it will never “knit” together, so the surface will never be correctly compacted if the base layer moves.
Quantity: The stone layer should be 5” (150mm) compacted depth when laid; ideally the stone layer should extend 50cm beyond the fence/kick boards so the perimeter drain is laid outside the arena.
Be cautious if your contractor does not specify the grade/quantity or depth of the materials being laid. Clearly if less stone is used, it will be cheaper and some contractors will reduce the specification and price in order to win the work.
2. Inadequate Drainage
There should be at least one drain across the school and one on the perimeter, on all sides. If the ground is heavy clay, additional cross drains should be installed and the diameter of the exterior drains increased. The drain runs should have a consistent fall.
If the drainage runs (trenches) are up and down (like a dog’s hind leg), do not lay the pipe with pea shingle (fine small pebbles, that are “hard”).
The tops of all the trenches should be covered with a fine grade (e.g., 4 oz.) non-woven geotextile membrane which will allow the water to pass into the drains, but prevent silt/sediment.
It is important to include drainage trenches on the outside of the arena. These external drains will stop the runoff from adjacent paddocks – so this is especially important if an arena has been cut into the slope. They are also important because the outside track typically has the heaviest “footfall.”
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These tips were provided by Martin Collins Equine Surfaces (MCES), which has installed over 2,000 arena around the world, at private farms, events, international shows and FEI World Cups in Europe.
Avoid purchasing unwashed sand for the equestrian surface.
3. Weak Fence Posts
Fencing posts should always be concreted in, as they need to support the retaining boards.
This combination should be strong enough to withstand the surface being packed against them, and able to endure being struck by any maintenance machinery.
4. Building at the wrong time of year/in the wrong conditions
It is best to build during a dry period, preferably in the summer.
Clay in particular needs to be carefully managed, especially during earthworks, such as “cut and fill,” so “clay heave” does not occur. (This is most likely to occur when wet and under pressure, which causes it to “bubble up”; this can move the stone layer and membranes, leading to contamination of the surface and poor drainage. Should this occur, remedial work will be required).
5. Incorrect cut and fill
Cut and Fill is the process of cutting into a bank, and relaying the material lower down the bank to create a “level formation” for your outdoor equine arenas. The banks/slopes must be created correctly to support the new formation.