Fine-textured soils such as Dermosols and silt loams are common across parts of Western Victoria, where bunker silos may face conditions that make sealing and surface protection especially important. Choosing high-performance silage plastic is not only about the top cover’s strength. The interface between the forage and the cover can determine how effectively it excludes oxygen from the stack. A thin, high-cling vacuum underlay can follow the contours of the fodder more closely than a standard heavy-gauge cover, helping reduce air pockets around shoulders, edges and uneven surfaces.
Why Standard Covers Can Leave Air Pockets
A conventional heavy-gauge cover provides valuable mechanical protection, but its weight and stiffness can prevent it from sitting tightly against every contour of a bunker. Unevenly packed forage can leave small channels or pockets beneath the sheet.
These spaces matter because trapped oxygen can support aerobic activity near the surface. The top shoulder is particularly vulnerable because it combines sloping geometry with greater exposure to movement, wind and imperfect contact.
A high-performance silage plastic system addresses this problem by separating sealing from physical protection.
How Vacuum Underlay Films Improve Sealing
A vacuum underlay film sits directly against the forage beneath the heavier outer sheet. At around 40 μm, this ultra-thin film conforms closely to the surface, including shallow depressions and irregular contours.
The key benefit is contact. Rather than relying on the weight of one thick sheet to create a seal, the underlay follows the forage profile and helps limit air-filled spaces.
A vacuum-underlay high-performance silage plastic system can therefore provide a more effective sealing layer. At the same time, the heavier cover above it supplies additional resistance to punctures, abrasion and weather exposure.
Protecting the Top Shoulder
The shoulder area deserves particular attention during bunker sealing. Poor compaction, sharp changes in the slope or insufficient overlap can create areas where the cover does not maintain close contact.
Before covering a bunker, operators should check:
● Whether the forage has been adequately compacted
● Whether the shoulders are smooth and well formed
● Whether the underlay reaches the edges and contours
● Whether the outer sheet provides sufficient physical protection
● Whether overlaps and perimeter seals are secure
Using high-performance silage plastic as part of a layered system can help address both sealing and protection requirements.
Underlay vs Standard Cover
The two products serve different purposes and are not direct substitutes.
Vacuum underlay film:
● Conforms closely to uneven forage surfaces
● Helps minimise air pockets
● Creates a sealing layer directly over the silage
● Is particularly useful around shoulders and contours
Heavy-gauge outer cover:
● Provides greater mechanical protection
● Resists handling damage and environmental exposure
● Protects the underlying sealing layer
● Works as part of a complete bunker-covering system
For bunker pits on fine-textured soils in Western Victoria, this combination can be more practical than relying on a single sheet to provide all functions.
Installation Still Matters
Even the best high-performance silage plastic cannot compensate for poor bunker preparation. The forage should be compacted properly, the surface shaped to shed water, and the shoulders formed without abrupt depressions.
Place the underlay carefully so it stays in close contact with the forage. The heavier cover should then be positioned without dragging it across the underlay or creating unnecessary folds.
Conclusion
A heavy-gauge cover protects a bunker, but a thin vacuum underlay performs a different and important job: maintaining close contact with the forage and reducing spaces where oxygen can remain. For Western Victorian bunkers built on Dermosol and silt loam sites, combining a conformable underlay with a durable outer sheet provides a practical approach to sealing and physical protection.
Choose high-performance silage plastic based on the complete covering system, not the outer sheet alone. Speak with an agricultural plastics supplier about vacuum underlay and heavy-gauge cover options suited to your bunker design and operating conditions.
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Frequently Asked Questions
1. What is a vacuum underlay film?
A vacuum underlay film is a thin sealing layer placed directly over compacted forage beneath a heavier protective cover.
2. Why use an underlay beneath a heavy-gauge cover?
The underlay can conform more closely to forage contours, helping reduce air pockets that may remain beneath a thicker outer sheet.
3. Is a 40 μm film suitable as a bunker underlay?
A 40 μm film can be designed for close-contact sealing applications, but suitability depends on the product specification and the bunker conditions.
4. Can an underlay replace a heavy-gauge cover?
Generally, the two layers have different functions. The underlay provides close contact and sealing, while the outer cover provides additional mechanical protection.
5. Why are bunker shoulders important?
Shoulders can be difficult to seal because of their slope and shape. Poor contact in these areas can leave spaces beneath the cover, so careful compaction and covering are especially important.
