Build Concrete Storage Silos Using Cardboard Tubes and Styrene
by Fred Barkhouse Jr.
The Cloverleaf Cement plant is a large Portland Cement producer that was once served primarily by ship, but is now served by the Windsor & Midwestern railroad. One of the dominant features of a Cement plant is large concrete silos for storing dry bulk commodities. We combined two Valley Cement kits from Walthers as the start of the Cloverleaf facility, but soon realized we needed more silos, a lot more!
We utilized two different methods to create the silos for the Cloverleaf Cement plant, as well as using the silos in the Walthers kit. The main receiving complex silos were created using PVC pipe, the kind used in household plumbing, and the larger diameter silos on the packaging building were made using cardboard tubes covered with styrene.
Before starting any project, it is helpful to have a very good idea of what you want the end product to look like. Scale drawings are not necessary, but can be very helpful. I started this project with a very distinct image in my mind of how the building should look finished and also measurements from the area the building would be placed to help with overall size.
The tubes I used to construct these silos are the kind used in rolls of industrial plastic wrap. One of our members grabbed some from work, they are just tossed in the recycling anyway, so using them for silos is a great way to save some money and reduce waste! These tubes have very thick walls, about 1/4″ and are about 3″ in diameter which works out to about 25′ in HO scale. Cardboard tubes come in all kinds of sizes, so it is just a matter of finding some the diameter you are looking for. While thick walls are not needed, they do help by making the final building stronger.
After locating the correct diameter tubes, we’ll have to cut them to the proper length. The tubes I used were 12″ long, about 90′ in HO scale. I wanted this building to look very large compared to the railcars that would be parked around it, so I didn’t trim the tubes down. Had I wanted to cut the tubes, I would have used the crop-saw at the club to do it. Using a band saw would be easiest if you have one, but any saw will do. Just be careful to keep the cuts square as the ends of the tubes form the top and bottom of the silo.
A storage silo complex is made up of many silos joined together. For this complex I used five silos. I used hot glue to attach the tubes to each other.(fig. 1) To keep them square I clamped a piece of 2×4 to the edge of the table and used a square line up each tube before gluing. The 2×4 keeps the bottom edge even and the square ensures silos don’t lean to the sides. Being laid flat on the work surface assures the silos don’t lean forward or back.
Most cardboard tubes are made by winding a strip of paper around a cylindrical form on a diagonal. This creates a diagonal line that spirals around the tube and runs from one end to the other. This line is not prototypical for concrete storage silos! To hide this seam, and provide a better surface to paint later, I chose to cover the cardboard with styrene.(fig. 2) Styrene is a type of plastic, used regularly in the model train hobby. It is very easy to work with and available in a wide assortment of thicknesses and textures. If you are planning to do a lot of scratch building, look into buying styrene by the 4’x8′ sheet, it is far cheaper then buying the small pieces sold at most hobby shops. Try looking for plastic resellers or custom sign shops in your area.
We had part of a sheet of 0.020″ thick styrene on hand, so I used that. I would recommend using 0.040″ though, as some lumps and bumps showed through the thinner stuff I used.
Now you need to make a decision about the appearance of your silos. Some silos look like vertical cylinders standing next to each other, the surfaces of adjacent silos curve into each other and meet at the point, while others have a flat filler panel between each silo. I like the look of the flat panel between silos so I went with that. They are also mush easier to make this way!
I started by cutting a strip of styrene the same height as the silos. Then I measured the circumference of the face of the silo that would be visible. If you are using the flat filler panels, you don’t have to be exact with this measurement, as the panel will cover any errors. I then cut strips from the styrene to cover the fronts of the silos, because these silos are against the backdrop I didn’t put styrene on the back side. The end silos need larger strips that can wrap all the way around.
With all the strips cut, it is now time to glue them to the silos. I started by running a bead of hot glue down the silo, following the joint between tubes. I used a board to hold the styrene strip flat in the glue until it set. If you are not using the flat filler strips between silos, you’ll need to use thicker styrene as the stuff I used deformed a little from the not glue. Once the hot glue set, if spread Weldbond white glue over the surface of the tube to be covered.(fig. 3) In hindsight, I should have been more careful to spread the glue evenly, as the globs didn’t smooth out under the thin styrene as much as I thought, and caused some lumps in the silos. So, learn from my mistake and spread the glue smoothly and use a little thicker styrene.
I ran another bead of hot glue down the other side of the tub and used the board to push the styrene strip into the white glue and rolled it over to the other side and into the hot glue.(fig. 4) Keep pressure on the hot glue until it sets. The hot glue holds the styrene in place while the white glue dries. Use the same technique to finish covering all the silos. I was able to build this set of silos in a matter of hours using this technique.
As you can see from the photo (fig. 5), the seams between the silos are very visible and don’t look good at all! Now it is time to hide those with the filler strips. Using that same piece of styrene that I cut to the height of the silos, I cut 1″ strips to use as the filler pieces. You’ll have to adjust the width of these strips to suit the size of your silos and the appearance you are after.
I simply laid the strip in the opening between the silos and glued it in using Pro-Weld. Any solvent type glue for styrene would work for this step. Take care to keep the strips square to the silos or it will look like the silo is twisted when you finish. The strips should also be parallel to the length of the silos. At right you can see I have already glued two of the filler strips in place (the right most silos) and an unused strip is set on top of the silos.
Now it is time to build the top of the silos. I turned the silos upside down and drew their approximate dimensions out on a piece of the same styrene. I cut this piece out as a large rectangle and glued that to the top of the silos. I used hot glue around the top of the silo at one end and glued the top to that silo first. I then applied hot glue to the last silo and glued the other end down. With both ends glued on, I placed the silos with the top down on the work bench and glued the top styrene to the silos using Pro-Weld.(fig. 6)
After the glue dried thoroughly, I used a sharp #5 blade to trim the extra off the roof so that was flush with the edge of the silo. If you want a smooth faced silo, you can fill and sand this seam smooth and move on to painting. I decided to add a small lip to the top of the silo, as this is a common practice and hides the seam much quicker then filling and sanding! I used strips of 0.020″ x 0.060″ styrene glued along the top edge of the roof to form the lip (fig. 7). This has the added benefit of reinforcing the joint between the roof and the silo sides. The styrene is thin enough that I didn’t have to cut it to fit the curves of the silos, it just bent to fit. If you want a thicker lip, I’d recommend layering several thin strips rather then using one thick one, as it will conform to the curves of the silos better.
I used a damp cloth to wipe the styrene sides and top clean before painting.
I painted the silos using large spray cans, the kind you get from home improvement stores or some craft stores. I find these are more cost effective and faster then airbrushing for large buildings. The spray cans are available in a wide assortment of colours, but I still haven’t found a concrete colour that I like. I started by spraying the whole structure with a medium grey primer. When that was completely dry I sprayed the concrete colour. Cloverleaf Cement painted a green band around the top of its silos, so once the concrete was dry I masked the area to be green and sprayed that with an airbrush. I was aiming for an old, weathered look, so I didn’t try for a solid coat of green, I intentionally let some of the concrete show through. Once the green was dry I sealed the whole building with a clear flat finish. I like to weather over a flat or semi-gloss finish rather then a glossy one. If the paints you use dry flat, then you can skip this step and get right to weathering.
Weathering to be added as soon as I finish them.