Mountain Tunnels - Part I

By Ty’s Model Railroad - 5/25/2011 08:34:00 PM

A completed expanded foam tunnel base structure with styrene tunnel portals at each end

Before I could start the mountain and tunnel, I had to finish the track. First was paint. I experimented for a few days to find a method that covered quickly and looked realistic. Since my layout is right beside my furnace and hot water tank and and lacks ventilation, spray paint and enamels were out of the question. That left me with hand brushing with water-based acrylics.

Three curved tracks with their ties painted with brown acrylic paint

To paint the track I used Burnt Umber acrylic. I mixed it with a bit of grey and thinned it with 25% water and 25% isopropyl alcohol. This mixture covered well and dried quite uniformly on the ties and in the webs of the rails. I had to use extreme caution when painting the turnouts, making sure I moved them frequently while the paint dried so they didn’t get stuck in place. Once the paint was dry, I cleaned any paint off the top of the rails using a fine grit sanding block.

Atlas turnouts with their ties painted with brown acrylic paint

A slightly curved track leading into a 60 degree rail crossing with brown painted railroad ties

I also temporarily placed my previously built tunnel portals at this point. This allowed me to determine the exact location of each portal and the overall size that my mountain and tunnels needed to be. Due to spacing limitations, I had to combine the small and large portal on the tunnel entrances on the right hand side of the mountain. I cut off 1" of the left base of the large portal and glued it to the top of the right side of the small portal. This now allows both portals to exist where they were both intended to be.

A single and double styrene tunnel portal placed on model railroad track to test fit

A single and double styrene tunnel portal placed on model railroad track to test fit

With the track and tunnel portals complete, I could finally start building the large mountain which the two tunnels will run through. Before I could build the mountain, I needed to build each tunnel structure which the mountain scenery will sit on. Each tunnel includes support walls and a common ceiling which acts as the base for the mountain.

Two single and two double styrene tunnel portals placed on model railroad track to test fit

The first task was to add an access point to the lower tunnel to rescue trains in the event of a derailment. The double wide tunnel is wide and short enough that I can access the inside from either end. The smaller, single tunnel which goes under the double tunnel is much longer and narrow and I cannot fit my hand through the portals. To solve this, I cut an opening in the benchwork right beside the track, allowing me access the track from underneath.

A triangular hole cut through the benchwork next to the model railroad track in the future tunnel

To keep the inside of the tunnels as dark as possible, I painted everything inside with black paint. Since there were sections of tunnel that didn’t have a complete wall to divide them, it was important that everything was blacked out so no light could leak through. I used cheap black acrylic paint from the dollar store, which worked great for this purpose.

Benchwork and foam painted black around track in the location of the future tunnel

I used Styrofoam to start building the walls. I used a combination of white glue and toothpicks to hold the foam together and keep it in place while the glue dried. Once dry, each wall section was painted black. I did visual checks on each end with my plastic tunnel portals in place to ensure that no wood or white Styrofoam was visible from any angle. If there was, I quickly covered it with black paint. 

Expanded foam panels being installed beside ballasted train track to form tunnel walls

It was at this point that I realized that I almost forgot to ballast my track on the inside of the tunnels! This was an important step as the track will still be visible for a distance into each tunnel and would look very odd unfinished. Adding ballast after the tunnels were completed would also be very difficult. 

A set of half ballasted model railroad tracks coming out of a styrene tunnel portal

I used Woodland Scenics Medium Buff ballast. This, like most everything else, was my first time ballasting track. Doing the tunnel sections first was a great place to start and practice as they will be a lot less noticeable once the tunnel is complete. 

A ballasted model railroad track leading into a styrene tunnel portal

I used a ballasting method that I found to be most popular in my online research. This method is to lay the ballast on the track and shoulders, then use a brush to level it between the ties and make it uniform. Using alcohol and an eye-dropper (pipette), gently wet the ballast. This reduces the water tension when adding the glue, allowing it to wick better through the ballast. Once the alcohol soaks in, apply a liberal amount of white glue, thinned 50% with water and let this soak in as well. Be careful not to add too much glue at once or your ballast with start to flow away. Once the glue completely cures (about 24 hours) the ballast will be hard as concrete.

Expanded foam panels being installed beside ballasted train track to form tunnel walls

One thing I learned from this first ballast attempt is to not use too much ballast. You can always add more but using too much makes things messy, and it’s almost impossible to brush all of the granules off of the tops of the ties. Model Railroader Magazine has a really good article in their February 2011 edition about ballasting track. They explain a two-part application process of ballasting, where you first apply glue, then ballast, then re-apply ballast and glue again. This method looks really nice in the end. I just might try this when I complete the rest of my track. 

Expanded foam and basswood panels being installed beside ballasted train track to form tunnel walls

Expanded foam and basswood panels being installed beside ballasted train track to form tunnel walls

The entrance to each portal is the most visible so it was important that there were complete walls on both sides of each portal. These needed extend far enough into the tunnel so you could not see that it ended. I places I didn't have room for Styrofoam walls, I used 1/16” basswood as a divider. This prevented light from entering either of the portal entrances, showing through to either the top or lower tunnels.

Expanded foam and basswood panels being installed beside ballasted train track to form tunnel walls

Once I ensured the tunnel portals fit correctly, I did a final visual inspection to make sure everything was pitch black inside. I then used a large template to cut a solid foam roof panel for the entire tunnel structure. I attached foam supports on the backdrop to support the back and left edge of the roof structure. I painted the roof and foam supports black then and glued it into place.

Expanded foam and basswood panels being installed beside ballasted train track to form tunnel walls

Any gaps were filled in with carefully cut pieces of foam. Upon my final inspection, there was not a single sliver of light visible inside the tunnels. Now I have a solid tunnel structure which my mountain can be built upon without any possibility of affecting the tunnels themselves.

Expanded foam and basswood panels being installed beside ballasted train track to form tunnel walls

A completed expanded foam tunnel base structure with styrene tunnel portals at each end

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