Storage: Floors that last – materials, installation critical

Forages are the base of all dairy feeding programs. Forage storage areas need a strong base, too. A generation ago almost all bunker silo floors were made of concrete, but increasingly farmers are using asphalt for silo floors.

By Everett D. Thomas

In spite of very low milk prices, dairy farms will continue to expand, and as they do, most will need added silage storage. Most new silos, especially on larger dairies, are either bunkers or stacks (also called drive-over piles).

Much of the cost of these silos – the entire cost in the case of stacks – is in the silo floor. We want silo floors to last a long time, which means first choosing the best material, and then making sure the installation will result in a long-lasting surface.

The only really long-lasting silo floors use either concrete or asphalt. A generation ago almost all bunker silo floors were made of concrete, but increasingly farmers are using asphalt for silo floors; first for bunker silos and, more recently for stack silos as well.

And why not; in spite of higher petroleum costs, asphalt floors are still somewhat cheaper than concrete ones and will last much longer.

How much longer? Based on our experience at the William H. Miner Agricultural Research Institute, Chazy, N.Y., plus my travels throughout the United States, an asphalt silo floor will last at least twice as long as concrete. It’s hard to be more specific when most concrete floors must be replaced after 10 years of use, while many asphalt floors are still in excellent condition after 20 years or more. I’ve seen 25-year-old asphalt silo floors in Idaho that are still as good as new, with no maintenance or repairs.

‘Chemistry 101’

The reason asphalt lasts so much longer is “Chemistry 101”: Concrete is lime-based and silage is acidic. The first day forage is put onto a concrete silo floor, a gradual process begins that will deteriorate the surface of the concrete. Eventually, the aggregate in the concrete will be exposed by the action of silage acids, and it will be increasingly difficult to keep the surface clean.

Asphalt, on the other hand, is petroleum-based and therefore unaffected by silage acids. Once asphalt is installed, no coating or other maintenance is needed – other than keeping the surface clean – and that’s just good silo management, not because it necessarily extends the life of the asphalt.

Installation: Do it right

While asphalt is the best choice for silo floors, the installation job must be done right. This means an excellent, well-drained gravel base that’s very well compacted. A very firm base is a must, because while concrete will bridge surface depressions, asphalt will not. What’s really needed is an asphalt contractor who can build a “road-quality” surface. This means care should be used in selecting a contractor, and the one with the lowest price might not be the one to choose.

For new construction, asphalt is installed in two layers, or “lifts.” The first is coarse aggregate, and the top layer a finer aggregate that results in a smooth surface. Asphalt contractors vary as to the thickness of each lift, but most finished floors in new silos are 4” to 6” thick. All working edges must be protected by a concrete ramp to prevent traffic damage.

Resurfacing existing silo floors

Worn concrete silo floors can be resurfaced with asphalt, and at a fraction of the cost of new construction. We did this several years ago at Miner Institute, and have been pleased with the results – and the price.

First, the old floor is cleaned to remove all old silage and loose aggregate. Then the asphalt contractor will spray on a material to increase the adherence of the asphalt to the concrete.

In resurfacing projects, only one layer of fine aggregate is needed, with the asphalt installed “edge to edge.” That’s because asphalt and concrete have different coefficients of expansion, and patching worn concrete areas with asphalt isn’t recommended.

We don’t know as much about the useful life of asphalt over eroded concrete, but know of one “resurface job” that after five years was still in mint condition.

Asphalt is fine in warmer climates, as long as a good job is done to start with. I’ve seen silos with daytime temperatures of 90 F or so, and there’s no softening or deterioration of the material. The first two asphalt floors we installed were “acid tests,” so to speak, because they were 25’ wide silos, so most all traffic was right down the center of the silo floors. If there was any situation where the combination of hot weather and heavy traffic would result in depressed traffic lanes, this would be it. There was no problem at all.


• Ev Thomas is a consultant with Oak Point Agronomics, Hammond, N.Y., and continues to work part-time for Miner Institute, Chazy, N.Y. Reach him via phone: Cell 518-570-7408; e-mail: or visit

• For additional information, visit Floors for Bunker and Stack Silos.pdf