Not sure what size Grain Bunker Size you need for your desired capacity? Try our Grain Bunker Calculator.
Not sure what size Grain Bunker Size you need for your desired capacity? Try our Grain Bunker Calculator.
Fumigation is one of the most effective tools for quality control in addition to clearing pests and insects out of stored grain, however it comes down to one thing: the seal. Phosphine and other fumigants only work when the gas is held inside the storage at a high level of concentration for the full exposure period to kill every stage of the insect. In an improperly sealed bunker, the fumigation gases escape and the concentration drops too low to kill the insects. You have still paid for the chemical and the labour, but the treatment has not worked. Worse, the insects that survive tend to be the most resistant ones, so the problem gets harder to fix next time. This guide covers how to seal a grain bunker properly so that when you fumigate, it actually works.
A fumigant is a gas, and gas follows the path of least resistance. If there is a gap at the perimeter, a hole in the cover, or a loose join, the gas bleeds out faster than it can do its job. Effective fumigation depends on holding the target concentration across the full exposure period set out on the product label and in current industry guidance. A poorly sealed bunker cannot do that. It wastes chemical, leaves live insects in your grain, and contributes to the phosphine resistance that the whole industry is fighting. This is why the accepted rule is simple; only fumigate in storage that is sealed gas-tight and treat sealing as the foundation of the whole operation rather than an afterthought.
A gas-tight bunker starts with the same envelope as any well-sealed bunker: cover, ground sheet and wall system. For the full walkthrough of that setup, read our recent blog on How to Seal a Grain Bunker the Right Way. What fumigation adds on top is a way to work the bunker without breaking that seal once it’s closed.
Next is the dosing and sampling access. Rather than lifting the cover and breaking the seal, you fit fumigation zips at chosen points, which let you introduce product and take grain samples while the bunker stays closed. For the tarp itself, custom fumigation tarps are made to your requirements so the sealed enclosure fits the way your bunker is actually built.
Then there is the base and the walls. Concrete bunker walls give the most secure and permanent fixture and provide superior sealing compared with open pads, which is a real advantage when gas retention is the goal. A ground sheet under the stack completes the envelope by sealing the floor against moisture and reducing leakage paths from below.
Start before harvest, not on fumigation day. Size and specify a gas-proof cover for your bunker and if you are building new, choose a wall system that seals well. Concrete walls are the benchmark for sealing and a well-formed pad with a proper gradient sets up both drainage and a clean edge to seal against.
When the bunker is filled, lay the cover so it sits flat over the grain with even overlap on all sides. The classic on-farm method for sealing the perimeter is to run soil along the tarp edge to pin it down and form a continuous seal against the ground, and many growers also weight the cover with concrete tyre weights to hold tension and stop wind lifting the edges. A cover that flaps is a cover that leaks.
Before you treat, inspect the whole envelope. Walk the cover and check for holes, tears, worn spots and loose joins, because a single unrepaired hole undermines the entire seal. Address any damage promptly with repair tape and sealant from the tools and accessories range so the surface is continuous. Only once the bunker is genuinely sealed should fumigation take place, always following the product label and current industry directions and using appropriately trained or licensed people to handle and apply the fumigant. Polytex supplies the sealing hardware that makes effective fumigation possible. It does not replace label directions or professional advice on the chemical itself.
The same principle applies to silos. A silo only holds a fumigant if the base is sealed, and a common weak point is the join between the silo wall and the concrete pad. Glo-mastic, a solvent-free acrylic sealing membrane, is designed to create a continuous water-tight seal and adhesion between the silo and its concrete base, closing one of the leak paths that lets gas escape. Sealing the silo base is a must for effective fumigation in the same way that sealing the perimeter is for a bunker.
A seal is only as good as its condition on the day. Inspect covers before every season and after weather events, repair damage as soon as you find it, and store tarps well away from sunlight when they are off the bunker so UV does not shorten their life. Good site hygiene around the bunker, combined with a well-sealed cover, also reduces the pest pressure that makes fumigation necessary in the first place. If you want a proven method for building and running bunkers that seal well, the Grain Bunker Construction Guide collects years of advice from Australian growers and bulk handlers into one resource.
A seal is only as good as its condition on the day you fumigate, not the day it was installed. Recheck the envelope before every treatment, not just once a season, as a hole that’s opened up since your last check is enough to undermine the whole job. Good site hygiene around the bunker also reduces the pest pressure that makes fumigation necessary in the first place. For the full detail on building and maintaining a seal that holds up over a season, see How to Seal a Grain Bunker the Right Way
Most failed fumigations come down to a handful of avoidable errors at the seal. Watch for these before you treat.
Sealing is far easier when the bunker is designed for it. Work out your capacity, dimensions and cover sizing with the Grain Bunker Calculator, and for a complete setup consider an on-farm grain bunker package that brings the cover, ground sheet and securing options together with expert advice. Australian made, delivered nationwide, and built for the conditions your grain has to survive.
Ready to fumigate with confidence? Contact the Polytex team or call 1300 059 003 to spec gas-proof covers, fumigation zips and the right sealing setup for your bunkers and silos.
