Building a Model Railroad – Part 8: The Backdrop.

Having assembled half the baseboards in the last update I decided it would be good to move on to the section of backdrop along the wall. Since the baseboards aren’t yet screwed to the benchwork this made everything a lot more accessible. I didn’t work at it very diligently (because Summer) but I finally got the base layer of paint down about a week ago and decided it was time to share my progress.

Because the wall sections have pieces of J channel over the edges of the drywall, I needed to pad out the wall so that the backdrop wouldn’t bow out when it went over each joint. I did this by tacking 1.5″ strips of 1/4″ thick plywood horizontally along the top and bottom edges of the backdrop boundary and vertically over each wall “stud” (strapping). At this point these shims are just held in place with a few finish nails. Nothing more is needed as the screws for the backdrop will go right through them later.

Before attaching the strips, I measured 1/4″ up from the baseboard in one location and then used a level to draw a line across both walls to mark out the bottom edge of the backdrop. There will be at least an additional 1/2″ of sub-base on top of the current 1″ of foam so that will overlap the edge of the backdrop and someone standing from a regular viewpoint shouldn’t be able to see a gap. Hopefully.

With the prep work done It was time to start hanging the backdrop. I decided to use 4′ x 8′, 1/4″ PVC sheets ripped down to 2′ x 8′. All scenery on the backdrop will be painted on these panels but the blue for the sky will extend all the way up the wall to the ceiling. While it would have been nice to extend the backdrop all the way up, that would have meant more waste as a full 4′ sheet wouldn’t fit. At nearly $50 a sheet, I definitely wanted to use every little bit.

I bought my PVC sheets from Home Depot. They’re rigid enough to need relatively little support but flexible enough to bend with ease. They are smooth on one side and have a wood grain pattern on the other. I am, of course, using the smooth side. They cut like butter with a circular saw or jigsaw and can also be scored with a knife and snapped just like Sheetrock. This was especially handy for making final cuts in the basement where a saw would have made a mess and incurred the wrath of my wife and child who are usually asleep directly above the layout room while I’m working.

I started the backdrop at the rear corner which seemed like the obvious place since the cove and window frame meant that there would not be much room to play around with the fit. As you can see I had to notch the upper corner to clear the trim. Each end of every panel lands in the middle of one of the shims. The panel is secured to the wall with standard drywall screws that I pre-drilled and countersunk holes for.

In order to reduce the risk of the sheets bowing away from each other to differing degrees I decided to glue the edges together. Since ventilation in the basement is poor and any smells invariably find their way upstairs to the living spaces of the house I went with an odorless PVC cement, which does have a bit of an odor but only if you stick your nose right inside the can. When the joint was curing on the wall I couldn’t smell a thing.

Unfortunately due to slight inconsistencies in the walls some of the joints ended up being a bit too wide to be glued. To get around that problem I took some shavings that had accumulated from countersinking the screws and mixed them with cement in a glass jar (similar to the “Sprue-goo” technique that many of us use on our styrene based models). The resulting “sludge” for lack of a better term was thick enough to fill the gaps after a couple of passes. Since it’s pretty difficult to sand I tried not to spread it all over the backdrop.

Having progressed most of the way along the wall toward the front of the house I needed to make a decision: Should I continue the backdrop straight along the wall, terminating at the end of the benchwork as I had planned, or should I curve it around to terminate at the layout entrance. I had originally thought that I would want to be able to take photographs of trains from outside the layout looking back through Bridge 14, but I ultimately decided that since this is a mostly inaccessible angle on the prototype I would much prefer to have the backdrop continue around the layout and hide the electrical panel.

To facilitate this I had to build a framework of sorts off the benchwork to support the backdrop. Since this would need to be pretty strong due to the coved corner I elected to rip down a 2×6 for the vertical and horizontal supports. An additional piece of scrap 3/4″ board provides a place to screw down the lower edge of the backdrop once it transitions out of the curve.

This second coved corner was a bit more complex than the first one as the cutout for the window frame was in the middle of the piece as opposed to at the end. Figuring out exactly where to cut for the notch was a bit of a puzzle but I ultimately did it by bending a batten strip under the window and marking where it met the window frame. I then laid the batten on the PVC sheet and transferred the marks. I used a jigsaw to cut the notch out.

With the final sheet of PVC in place I cleaned up the benchwork and stood back to get a sense for how the layout would feel. I do wish that the backdrop went all the way to the ceiling but having it lower will help with airflow in the room and up close I don’t think it will really matter as the backdrop is more than high enough for the landscape I plan to paint on it. I am very glad that I decided to transition it around the front of the layout. It makes the electrical panel much less obtrusive.

Next I moved on to filling the screw holes and cleaning up the joints between PVC sheets. For that I used run-of-the-mill pre-mixed drywall compound, smashing it into the screw holes and spreading it out fairly wide around the joints so that I could feather it in and hide any bulges.

I had to sand and repeat the filling process a few time but eventually I got a pretty good finish that seemed like it would take paint well. The cove at the front of the layout also required a bit of dressing up. Using some scrap PVC I filled in the notch created by the window frame. Gluing everything together with the sludge. This looked a lot better than leaving it open and should be mostly invisible to casual inspection once everything is painted.

I messed up and glued the bottom part of the notch with the wood grain side up. Oh well, it’s not very visible.

I also wanted to fill in the tops of the coves to keep debris and dust from accumulating behind them and avoid a light well that would make those areas too dark. Everything above a certain point will be painted the same color and I’m hoping there won’t be many shadows once the layout lighting is in place.

I elected to make the filler pieces out of some scrap 1″ foam since it’s so much easier to cut on a curve than the PVC is. I glued the pieces in place with some regular construction adhesive then filled the gaps with Woodland Scenic’s Foam Putty. This stuff sands down nicely and is very easy to apply. I plan to use quite a bit of it on the layout scenery.

With all holes and irregularities filled and sanded the backdrop was finally ready for the first coat of paint. I’ll go into this process in more detail in a future post. This is just the first coat that I’ll be applying as the real painting won’t begin until the lighting is installed. I did want to use this first coat to practice blending a lighter blue into a darker blue to simulate how the sky changes color as your eye moves up from the horizon.

Both colors applied.

I started by painting a strip of dark blue across the top of the wall and backdrop. Once that dried I painted a strip of lighter blue along the bottom of the backdrop leaving about an 8″ gap between the two.

The paint dried much faster over the joint compound than it did on the PVC. This was a bit concerning at first… Fortunately it evened out over the course of a couple hours.

After letting both colors fully dry I blended them together with a further application. Working in short sections of about 4 feet at a time, I painted another strip of dark blue across the top of the remaining white space overlapping the dark blue that was previously applied. I then followed the same process for the lighter blue. Before either color had a chance to dry I ran a roller up and down partway over both to blend them into a third, medium blue, color. I fine tuned everything with a wide brush until I got a somewhat smooth gradient. I got better at this as I went along though I still need to work on my technique a bit. I’m definitely glad I chose to practice on this first coat.

With the walls entirely blue the room is quite a bit darker than it was and it doesn’t exactly feel like a bright spring day, however the layout lighting should fix that. For the time being though it’s just nice to see a part of the layout that doesn’t look like it’s still under construction!

The back wall. Layout South.
The layout entrance. North as far as the railroad is concerned.

I’m sort of taking a break from the layout at the moment while I finish up this seasons outdoor projects and do some modeling. Once the weather cools down and I can cocoon myself indoors I’m going to get started on the baseboards and backdrop along the other side of the layout. That will be quite a bit more complicated but I’ve got a vague idea of how to tackle it.

Till then,

  • Chris

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