A new SP bridge for Shumala, Part 3

In the previous post, I described completion of the girders for this bridge, including weathering (it’s at: http://modelingthesp.blogspot.com/2013/08/a-new-sp-bridge-for-shumala-part-2.html ). I also mentioned the need to glue a styrene sheet underneath the track ties on the bridge, so that it could be ballasted. Southern Pacific definitely preferred ballasted-deck bridges, and used that style even on long, high trestles. The problem was that the ties are Delrin or some similar engineering plastic, a notoriously difficult material to glue.
     After a lot of poking around on the Internet, often finding directly contradictory reviews of particular products (either “it worked great,” or else “it was terrible, didn’t stick at all,” and so on), I decided that the Loctite product, Plastic Bonder, had the best reviews. Then I couldn’t find it anywhere locally. But another Loctite adhesive, called Plastics Bonding System, got nearly as good reviews, and I found it available for sale nearby. It has two parts: an Activator, which is applied with a device just like a felt-tip pen, and an Adhesive, which is applied to one surface and the parts clamped (I just used clothes pins). I tried it and it appeared to work fine. I am not putting much stress on the joint, but it certainly sticks. I pried at it gently and the joint remained intact. Good enough for me.
     Then I was ready to install the girders. For bridges like this, one end normally has a shoe which can slide on its pedestal with expansion and contraction, while the shoe at the other end is bolted to its pedestal. (On larger bridges, the fixed end often includes a hinge which permits slight movement up and down, but not on a bridge as small as the one I am modeling.) I simulated the shoes and pedestals with small blocks of styrene under each end. This whole topic is described clearly in the book by Paul Mallery, Bridge and Trestle Handbook, Revised Edition, published in 1976 by Boynton and Associates, pages 31 and 32.
     I simply attached the girders with Canopy Glue, to the tops of the shoe/pedestal pieces. Here is a top view of the bridge at this point, with the sheet glued under the ties, using the Loctite system, to hold ballast.

     The proportions of the new bridge girders are far more appropriate for this short span than the ones used previously. This is evident in a view below, from the side, even before re-ballasting. That’s the Shumala depot roof in the foreground. The weathering mentioned in the previous post in this series (see citation at top) is visible in this photo, the yellowish rust film. Ballast of course remains to be added.

     Next I ballasted the bridge deck and surrounding area. First, I checked that I had a barrier to prevent ballast slipping around or through the bridge structure onto Chamisal Road below. Then I used my usual ballasting method, basically the Dave Frary approach (as shown for example in How to Build Realistic Model Railroad Scenery, Kalmbach). This is an entirely water-based method, using “wet” water (with a drop of detergent), applied with a misting sprayer, to wet everything thoroughly, then eyedropper application of a 50-50 mixture of wet water and acrylic matte medium.
     I have tried an alternate approach, advocated occasionally in the hobby press, to wet the ballast or other scenic material with 70 percent isopropyl alcohol before the eyedropper step, instead of wet water. But in all candor, I did not find it any more effective than wet water alone, and the alcohol seems able to soften some scenic materials. I’d rather not find out what else might happen along those lines.
     Here is the completed bridge. The girders look no different that what is shown in the two photos above, but this angle shows the completed ballasting.

    I’m happy to have a bridge back in place at Shumala. This scene is something I want to photograph as well as enjoy operating, and the bridge makes it more complete than it was.
Tony Thompson