1-Seven steps for seven piers. Starting on the left, the seven-step process to construct the piers resulted in seven piers ready to receive the base coat of paint. These steps involve the sizing and cutting of the square, bar, trailing edge and sheet shapes used to build up the piers. The Pier Table on the piece of paper was a very handy guide during the complete assembly process.
2-The second set of side panels added to the piers was cut at the angle of the side-slopes of the piers (see figure). To keep from marring the surfaces of the first set of panels, duct tape was used during the rough-shape sanding of the ends of the second set of side panels. The thickness of the duct tape leaves a bit of stock for the finish sanding seen to the right.
3-Once a base coat of the final concrete color was applied to the piers, additional random patches of spackling were applied, then the surfaces were sanded smooth. The purpose of this step is to remove the consistent smooth surfaces that are the result of the sanding sealer and sandpaper process discussed in the text. In back are pier 8 and the south abutment.
4-The piers were painted once again and a final bit of surface texturing was done. At random locations a very thin coating of spackling was applied and drybrushed with additional darkened paint. Another technique involved the use of a painted string to apply bands of darker color on the piers. The result: older piers that are well into surface decay due to life in the city.
Figure - The cross section of the sloping model airplane shape trailing edge and the location of a cut made to match the height of the piers are shown at left. While the first set of side panels installed were cut square, the second set of side panels were cut with their ends matching the slope of the pier sides as seen to the right.
Having previously shown the results of two bridge pier construction methods: 1) kitbashing a plastic kit and 2) using printed papers, cardstock and pine 1x2s as the construction medium (see pages 52 and 53 of the October 2001 issue), I wanted to chose yet another method for constructing the seven older concrete piers being discussed this month.
Looking at possible materials available for making this set of piers, I choose balsa wood. Cardstock was too weak, plastic sheet too costly and metal too out of the question. Simple balsa shapes that are available at nearly every hobby shop in the free world led me directly to the balsa display at the local hobby shop. The simplicity of the tools (blades, a Zona® saw, caliper, small trowel, straight edge and square) and finishing materials (sanding sealer/thinner, sanding dust, spackling, sanding papers and steel wool) made me chuckle, "I could if I just would" right there in the hobby shop!
The first task was to select the sizes and shapes of balsa needed. Photo 1 shows the shapes used for the piers. There is a standard square and bar shape along with the model airplane special shape "trailing edge." This shape is used at the rear edge of wings on model airplanes. The cross section is in the form of a right triangle (see Figure) and is very handy for making the sloped sides of the piers.
With the available shapes in mind, an assembly sequence was developed for each of the piers, including the number and size of stock pieces required. This sizing of the piers was done starting with the dimensions of the top surface of each pier - the Pier Table shown in Photo 1 gives the size of each pier. The top surface was the sum of two criteria: 1) the sometimes-odd footprint of the bridge shoes and 2) the sizes of balsa shapes at the hobby shop.
In addition to 1/8" sheet balsa (used for the top piece), the sizes of the remaining shapes were: 3/8"square, 1/8" x 1/2" bar and 11/2" trailing edge. The top edge of the trailing edge shape is 1/16" and this thickness was included when determining the dimensions for the top of each pier. With the assembly method determined for each of the piers, all pieces were cut to length.
Included in the Pier Table in Photo 1 is a listing of the consistent height of the seven piers as discussed last time. Each piece of square, bar and trailing edge was cut to a dimension of 1.312 (15/16"). This allows for the constant height minus the thickness of the top piece. By carefully cutting the pieces to length, I found there was little cleanup once the pieces were glued together. I did allow an extra .010 in length when making the cuts. The most important thing is to make each cut square.
With the pieces cut to size, the subassembly of the squares and bars got underway. As can be seen in Photo 1, the pieces of square and bar were glued together with one side flat. Two of the assembled pieces were then combined with a set of side panels to form the shape of the piers. Then a second set of side panels was attached to form the four slanted sides of the piers. Walthers Goo® was used for all assembly.
Photo 2 shows the initial finishing steps that were used. First, the secret weapon of woodworkers - duct tape - was applied over the first set of side panels. Duct tape does two things: First, it protects the already installed side panels during initial rough sanding (using 100-grit paper) for shaping the ends of the second set of side panels. Second, it ensures that there is a bit of clean-up material remaining on the ends of the second set of panels. This extra material (seen on the pier to the left in Photo 2) is for the final shaping using 220-grit paper. The pier to the right has had the final rough shaping completed using the 220-grit paper.
With the piers interiors and sides assembled, it was time to start the initial finishing of the sides (and tops) to look like older concrete. Once the shape of the piers was roughed out using the 220-grit paper, the final shaping of the sides was accomplished using 320-grit paper. As with all sanding this month, the paper was laid flat on the workbench, and the pier sides were sanded by placing a side on the paper and moving the pier in both linear and circular motions. This stage of the sanding takes about five minutes per side for a total time of 20 minutes per pier. By the way, all sanding dust was placed in a container for future use.
Next, the top piece of each pier was cut to size and the cap set in place using Goo. The sides were once again sanded with the 320-grit paper the sides of the piers were used as a guide during the sanding for forming the edges of the cap piece.
The final finishing starts with smoothing the visible surfaces of the piers. First, all holes due to open grain or any cracks in the seams left during assembly are filled. Referring once again to Photo 2, you will see defects in the wood and seams.
An easy way to fill these large openings is to use the sanding dust that remains after the previous sandings. Place a small pile of the dust on wax paper, add a few drops of sanding sealer (Testors Aero Gloss 71-4 Sanding Sealer) and use a small stick to mix the ingredients into a thick paste. Then, using a small trowel, spread the paste on the large grain imperfections and fill any cracks in the seams. Allow a drying time of about 15 minutes and the defects are filled with "home brew" plastic wood. (It sands and paints just like real wood!)
At this point, a sanding of all surfaces was done using 320-grit paper. Once this sanding is finished, the final filling and smoothing is done. The point here is to get the surface of the wood very smooth to the touch.
To do this smoothing, a number of thin coats of sanding sealer are applied with a small flat brush followed with a light sanding after each coat. Each of the first three or four applications of sealer are followed by a sanding using 400-grit paper. Each of the next two or three applications of sealer are followed using 600-grit paper. Then finally, an additional two or three coatings are each followed by a buffing with 000-grade steel wool. This sealing process will produce very smooth surfaces on the piers. The piers then received a base coat, by air brushing, of the concrete color of the piers. Once dry, the piers, while colored concrete, will in fact appear too smooth.
To bring the look of the piers to what was needed on the layout, two additional finishing steps were required. First, some random places on the piers were covered with a light coating of vinyl spackling as seen in Photo 3. Once dry, the piers are once again lightly sanded using 400-grit paper. A light sanding using this grit of paper will smooth the spackling and will slightly burnish the too-smooth look of the painted surfaces.
Then, a couple very light coats of the concrete color were applied. The coats should cover all the white, but the color should appear a bit lighter over the spackling. Next, a few sides received a very light partial coating of the spackling using a wet brush technique no sanding was done after the application. These areas were then drybrushed the concrete color. A bit of brown was added at some of the areas in order to slightly darken the coloring (see Photo 4).
A final trick used the tool shown at the top of Photo 4. The thread was painted using a brownish color and, while held parallel to the top of the pier, was touched randomly to some of the sides of some of the piers.
Once the piers were colored to my liking; they were sprayed with a couple of coats of Dullcote and set aside to dry.