Thanks to everyone who stopped by to help us mark the occasion. We might just make this an annual event!
Constructing the backdrop for the railroad has been a real learning experience. I didn't really have a reference to guide me, so I hope my trials and tribulations will be helpful to others. I have heard of modelers using styrene, sheet metal, drywall and Masonite for backdrops. Masonite seemed like the logical choice - strong, readily available and within our skill set. When we started the layout, we decided to install vertical 2 x 4's on 4-foot centers against the wall. These provided a strong support system for the back of the bench work and gave the Masonite something to attach to.
We realized early on that horizontal members were needed as well to provide support for the Masonite. We had already placed a horizontal 2 x 4 at the top of the wall so the "L" channel around the perimeter of the suspended ceiling would have something to attach to. We also added a horizontal member at the bottom of the backdrop and one midway between the top and the bottom. We cut these horizontal boards as carefully as possible so they were a press fit in between the vertical members. We used the molasses-colored Gorilla Glue at the joints, which expands as it dries if you have pre-wet the mating joints. This eliminated the need for screws or other hardware which could get in the way of attaching the Masonite.
We initially attached the Masonite to the wood framing using countersunk flat head drywall screws into the Masonite and filled the holes with drywall compound. I handled joints exactly as one would tape and finish drywall joints - place the abutting sheet of Masonite as close as possible to the previous sheet, then tape and "mud" the joint. The problem is Masonite does not have tapered edges like drywall, so it was a lot of work to disguise the joint and feather out the mud. Our basement has heat and A/C, but despite that over time a small crack would appear directly over the joint. I went back and tried to add another thin layer of mud, but this was a short lasting remedy. Furthermore, it was not feasible once we had painted the backdrop, since we blended light blue at the bottom into medium blue at the top. Good luck trying to match that color variation!
During a visit to Stephen Priest's layout in Kansas City several years ago, Stephen shared his technique of leaving a gap (about 1/4" to 3/8") between the abutting sheets of Masonite and filling this with Bondo auto body filler. He said it stuck like crazy and if you made your joint a floating joint (easier said than done), you would have no problems with expansion and contraction.
Another local modeler suggested we try Durham's Water Putty for filling our joints and screw holes. I tried it but did not like it at all. It does not seem to hold its dimensions after it dries - a small hairline crack always seemed to develop around the edge no matter how many times you sanded it. It is also tougher than nails to sand. My vote goes to Bondo.
We continued to affix the Masonite with drywall screws to the support members behind and at the joints. Unfortunately, this created a lot of screw holes to fill. I also learned that the screw creates a localized "dimple" in the Masonite, so it creates the need to fill a depressed spot 3-4 inches round. This was a very time-consuming task when trying to sand the Bondo.
On this very long 8-foot piece of backdrop, we realized that we would have to glue it all at once, as we could not pull it away from the wall once any part of it was attached. We took a 10-foot 1 x 4 and screwed it to the Masonite directly over the center horizontal support frame; also two short pieces on the middle vertical member. We had about a dozen small screw holes to fill afterwards, but no countersinking or filling depressed screw heads. Notice that we also painted the top two feet of the backdrop before mounting so we would not have to try to edge our painting against the drop ceiling.
In the original room, we used a documented technique of painting the backdrop with two shades of blue, working down from the top with the darker shade and up from the bottom with the lighter shade and blending the colors in the middle. I wasn't overjoyed with the results (you could see where you started and stopped each section), but it looked okay. Good luck trying to touch up the backdrop if you damaged it or goofed while painting a cloud. This was one reason I could never get enthusiastic about painting clouds.
I fully intended to paint the backdrop in the new room using the same technique...until our gallon of the darker shade of blue ran out. The original color was discontinued and even though we had the formula, the mixing color palate had also changed. Two attempts to scan and color match the old shade were disasters and the thinner consistency of the new paint did not blend well with the thicker consistency of the old paint we still had for the lighter color. After painting the backdrop in the new room twice with very poor results, I made the decision to paint ALL of the backdrop (new room and old) a single, uniform color. I don't regret that call for a minute.
An experiment we tried that worked out very well was the use of cardboard concrete forms ("sonotubes") to transition from the original layout room to the new room. We wanted to create as tight a curve as possible around the opening in the 10-inch concrete block foundation wall. It did not seem at all feasible to bend Masonite to a 6 or 7-inch radius, and I was reluctant to try styrene or other material as it would have different material properties from the Masonite and I felt we would always have a visible crack due to expansion and contraction.
I initially bought a 12-inch diameter cardboard tube at Home Depot, which we cut in half lengthwise. It was about 1/8" thick, the same as the Masonite, so I just glued the edge onto a vertical 2" x 4" at each end, intending to put the Masonite up against it. I tried to fill the gap with drywall compound, but it kept cracking. The cardboard was not very rigid and every time it got bumped, the joint cracked. In addition, we were trying to make a 12-inch diameter tube stretch to 12-3/4", which it did not want to do.
I finally went to a concrete contractor supply business and bought a 14-inch diameter tube, which was much heavier and a full 1/4" thick. We built out our framing another 1-1/2" and that was a better fit. Using a router, we then cut a groove in each of the framing members, 1/8" deep (half the thickness of the cardboard tube). We applied Gorilla Glue in the grooves and stretched the cardboard tube just a bit to fit into the grooves. After the glue dried, we had a continuous joint that was strong and ready to mate with the Masonite. As with the joints between sheets of Masonite, we left a 3/8" gap which we filled with Bondo.
The cardboard tubes are spiral wound and the seams show if not addressed. I used several thin applications of drywall compound to minimize their visibility. After painting, they are barely noticeable.
We spent the first few months of the year working on wiring the main line (Charlie) and working on the backdrop (Andy) so that all completed bench work was operable. Truth be told, we were pretty excited to get some trains running now that we could run from Latrobe to Swissvale by way of staging. The Train Nerd's Blog tells the story of our first two operating sessions in January and April.