A number of things can happen when water enters a grain bin. First, water can damage the grain and the bin. Vertical columns can form in the bin, or wet grain can stick to a side wall and form a solid block. The grain may adhere around the bottom of a steel bin.
Wet grain may rot, mold and develop a sour smell. There is also the possibility of heat build up, which can develop quickly if temperature cables are not present or maintained.
The cost to remove and dispose grain from the bin can add up rapidly, and removal can be dangerous if workers must enter the bin.
Even small amounts of moisture entering the bin can cause structural deterioration. Steel bins will rust out around the base, which could lead to replacement of the bottom ring or welding in new sections.
Concrete bins will deteriorate faster once the concrete surface starts to spall (break up, chip or splinter). Flaking and chipping can occur over large areas. Cracks can allow water to enter, and freezing conditions can make the crack larger. Damage to spouts in the bin bottom also occurs when water is allowed to seep through the bin.
FINDING THE LEAKS. Areas where water has ponded is a good place to start looking for leaks. Standing water will deteriorate most types of roofing.
Look for a reddish color on the roof surface, which indicates a mold or a bacteria that will attack the surface of the coating. Look for small holes in the surface or any change in the roofing, such as a soft, gummy surface, cracks or an "alligator skin" look. Any spouts or vents in a ponded area also need to be inspected.
Cracks in the roof coating are a good indication of a leak area. Cracks in the roofing are frequently caused by cracks in the concrete under the roofing. Most cracks in concrete structures form during or shortly after the building process, when the concrete shrinks or from stress during curing.
Cracks also appear in areas between two or more protrusions through the roof surface. Other likely areas for cracks to appear are where bins join together and where a headhouse or other structure sits on the roof surface.
Exposed re-bar (reinforcing steel rods in the concrete) should be repaired as soon as possible. When moisture and air are allowed access to exposed steel, rusting occurs. The steel will expand and break away the concrete.
When walking on the roof, be aware of areas that sound "crunchy" underfoot. This indicates an area where the concrete surface is breaking up under the roofing, and there is likely to be moisture trapped under the surface. Spalled areas appear on the surface and have a powdery, flaky or gravel look.
It is also important to check for loose roofing. If the roofing has lost its adhesion, it is just a matter of time before leaks will appear. Also, pieces of roof-ing can blow off during a high wind.
Carefully inspect the area where spouts enter the bin and where vents or blowers protrude through the roof. Look for any cracks in the sealing material and for areas that might have rusted or worn through the steel.
Spouts need to be monitored not only for grain leaks but also for water leaks. Check for holes or cracks in the steel. If rusted water lines are running out of the spout, water is entering the spout somewhere above.
Check blowers and vents for damage. During high winds, parts sometimes break loose. It is important to prevent rust around the base.
Usually the roofing is sealed around the blower base. Check to see if the roofing has come loose from around the blower. Dirt and water will catch in these areas and deteriorate the steel very quickly. Also, the flanges that attach the blower to the roof top must be sealed. Check the seal any time the blower has been removed and replaced. All bolts should be tightened securely.
It is easy to identify problem areas on metal roofing. Normally a metal roof is pitched, which eliminates ponded areas. Rust on a steel roof is an obvious indication of needed repair. Areas that are rusted and covered with dirt or grain will be vulnerable to severe deterioration.
Also, check the bolts that hold the roof to the frame or that hold the panels together. These should be tight and in most cases have a gasket or washer on the bolt. Any welds on the roof surface should be checked for cracks or rusting.
Most steel bins have overlapping panels on the roof. These panels should be inspected for a uniform seal and should have no dents or breaks along the edge.
The base of steel bins has always been a high maintenance area. The concrete base can break down mostly due to moisture laying on porous concrete. The seal around the base almost always leaks. Numerous products claim to stop the leaks but most do not work.
Seal the area around transitions and blowers to prevent air leaks. An area of high air pressure needs a product with good adhesion and flexibility to withstand the pressure.
Damage to the side of a concrete bin can develop from structural failure or weather. If large cracks occur on the sides, usually some settling has occurred in the foundation. The surface of the side walls will begin to flake when the re-bar is near the surface. Moisture penetrates the surface and the re-bar rusts then pops the concrete.
Expansion joints must have a good flexible material covering them to prevent leaks and should be checked for broken concrete around tie downs and for leaks in the cap.
REPAIR OPTIONS. Numerous types of roofing materials have been used on elevators. These materials are usually meant for other types of commercial buildings. It is difficult to find a material that will withstand the piled grain, dust, standing water and the occasional shoveling by workers.
Flexibility and adhesion of the product is most important. Grain bins are always moving because they are constantly being filled and emptied, and from equipment vibration.
Roofing materials such as hot applied asphalt with rock, cold process asphalt coatings and aluminum fiber coatings provide good protection for a short time but generally deteriorate quickly.
A black surface can reach temperatures as high as 180°F (82°C), which will also increase the temperature inside the bin. Asphalt-based products will dry out and shrink and are not flexible.
New products developed recently include single-ply or sheet roofing designed to form a sheet over the entire roof. This type of roofing is flexible and will last many years. A single-ply is attached with glue applied in a pattern or with fasteners.
Since most elevators have numerous protrusions that must be sealed, a single-ply roof is impractical. In these cases, polyurethane foam is used to help make a roof slope by applying more in the center and less at the edges. A coating is applied over the top. But foot traffic on the roof can puncture the surface. Once the coating is broken, the foam will absorb water and damage large areas of the roof.
A single component urethane coating provides the best protection. The two-coat system is designed to cover over any existing flat or low slope building and can handle harsh roof environments.
The system incorporates a highly flexible base coat with a white finish coat resistant to UV, ozone, rooftop pollutants and ponded water. The coating can be utilized with a polyester fabric to repair cracks, blowers, vents and spouts.
A urethane is bonded to the roof to form a monolithic surface, eliminating seams. A surface coated with a white finish may be as much as 60°F (15°C) cooler than a black surface.
Acrylic coatings offer the same good qualities as urethane, but cannot be used where water ponds. Acrylic does not require any mixing and can be used in conjunction with the polyester cloth to make an excellent repair material around spouts and flanges.
The acrylic coating can also be used for a base seal on steel bins. It will move with the bin as it is filled and prevent water from entering for a number of years. If water cannot enter the bin, there is no damage to the structure or the grain inside.
Sidewall repairs usually involve working on a platform that hangs from the roof. Common repair materials include a portland cement and sand mixture or an acrylic concrete mixture. These are usually troweled into the damaged area after all loose material has been removed.
Epoxy materials can also be used to make this repair. Epoxies are about four times stronger than average concrete and can be used over severely damaged concrete since it can penetrate into the existing surface to create a good bond.
Sidewall cracks can be repaired by using a caulk material to fill and seal the crack. More severe cracks must be bonded together with an epoxy injection system. If the crack is moving there is no way to ensure that the concrete will not break again. Therefore, flexible seals should be used if the structure is still sound. Epoxy can also be used to repair the base of steel bins, even if the concrete is severely broken and flaking away.
Below-grade expansion joints can be repaired with a urethane foam that expands when exposed to water, as opposed to air. This material is injected into the crack and will stay flexible.
Once it is determined that repairs or a new roof is needed, remove all loose materials from the roof surface. The area around all protrusions should be cleaned down to bare concrete or steel with a hand scraper or a small air-powered chisel. The entire surface should then be pressure washed to remove all the old material and dirt. The new roof can then be applied.
It is also important to make sure the correct product is being used for the type of repair being done. Another good idea is to use a contractor who gives a warranty on the product being applied.