By Ken Bennet, P.ENG. University of Guelph

Brooksbank runs a 150-acre food quality corn operation near Dresden, Ontario. His in-bin dryer stores the last of three batches of corn over winter. Although he keeps his plenum temperature relatively low (95oF-100oF),
this is still a situation that promotes bin wall condensation because the last load of corn will be dried during the coldest outside conditions. When the last 10,000 bushels of corn are sold around April, the wet layer of corn next to the corrugated steel wall will have spoiled. This layer (up to 3” thick) constitutes a considerable loss, not just in what is spoiled, but in maintenance time to clean it off as well as possible contamination of the good corn.

The most economical solution seemed to be in the addition of some type of insulation in order to maintain a warmer temperature around theperiphery of the grain, facilitating moisture removal. At first, board insulation was inserted between the upright supports on the outside circumference of the wall. Over the winter of 1997-98, the side of the bin shaded from the sun (the coldest) was insulated in this manner. This proved very beneficial, and demonstrated that a more permanent installation would be worth pursuing. The main problems to consider were adequate coverage, flexibility and durability. A two-component urethane foam had the most flexibility for any bin configuration and could take care of the uneven corrugated surface. Urethane is susceptible to mechanical damage, however, as well as to UV degradation. The other question was whether to apply it on the inside or outside. Brooksbank had heard anecdotes about spray foam insulation being used on the inside wall of grain bins and preferred that idea, since it would not interfere with the outside appearance. The challenge was to protect the foam which would be exposed to grain movement, moisture and low levels of UV light during the summer. The main concern was that if bits of foam broke or dusted off, they would contaminate the corn for food usage. In addition, if moisture diffused through the foam and condensed against the steel wall, there would be a potential for corrosion.

The researchers met Steve Reesor, P.Eng., of Great Northern Insulation of Woodstock at the Ontario Outdoor Farm Show in 1998. Reesor is an engineer and specialist in foam insulation. He pointed out that a food-grade urethane coating (Madison Chemical Industries, Inc. Product# 201-15) on top of the foam would increase durability as well as prevent water from reaching the steel. With the cooperation of his associates at BASF Canada Inc. and Madison Chemical of Milton, Ontario who donated the materials for this research, he was able to orchestrate a ‘cost to us’ contract at the Brooksbank farm. In 1998, Great Northern Insulation applied foam to the top 8 feet of his bin, beginning at the top of the vertical ventilation tubes to just a foot below the stirring auger drive rail. In Brooksbank’s experience, this was area where the spoilage was most severe. Over the next two winters, the bin has been observed in the spring for the tell-tale signs of condensation. Wherever the insulation is, there has been absolutely no grain spoilage. However, on the un-insulated bottom half of the bin, there was a good deal of corn adhering to the wall.

Reesor is very confident of the durability of this coating, having refined the application method over two years. He emphasizes the need to prepare the surface of the galvanized steel wall with trisodium phosphate (TSP) to insure adhesion. Galvanized steel is one of the more difficult

Estimated cost for this solution:
Surface Preparation	$0.75/sq.ft.
Foam	$1.00/sq.ft.
Coating	$1.50/sq.ft

surfaces to spray. The first year presented some problems with peeling where the wall was only pressure washed; however, after it was repaired with a full TSP preparation, the bond was exceptional. The bin will continue to be monitored through the 2000/2001 storage season with the anticipation of a more challenging environment. Brown points out that the last two years were exceptionally dry, and that this winter may be the real test as the expectation is for much wetter corn to come off the field. He also points out that this technique may not be for everyone, but may result in cost benefits for farmers contracting for premium food grade corn. Right now, it is possible to get a fifty cent premium for quality food grade corn.

1