Articles - Roadbed
01/20/2009
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For my third layout, an N-scale layout, I decided to try the AMI roadbed material. I heard from experienced model railroaders that if they were to do their layout over again, they would choose AMI Roadbed. So that's what I used.

Update: It is my understanding that AMI Roadbed is out of business. However, there is similar material available (for example "putty tape"; 3M makes "Scotchfil", which looks an awful lot like the AMI Roadbed).

Anyway, for laying flextrack, this is, in my opinion, the best method for laying track (I prefer it over cork roadbed). It allows some freedom and flexibility in laying track, and allows for creating a very prototypical roadbed profile. Long-time proponents of this material are the famous Reid Brothers (N-scale Cumberland Valley). Allen Keller's video (Great Model Railroads #10) of the Reid Brother's layout has a segment where they describe how to install the material. AMI Roadbed is a rubber-like material. It does not smell, nor is it toxic. It looks like a tar-like material. It is very sticky to itself and mildly sticky to other materials. One box contained one roll of 30 feet of the material.
Roadbed
If you want to easily remove the AMI Roadbed material in the future, just lay it out on the plywood or other material sub-roadbed. Make sure the plywood (or other) surface is clean, or otherwise the AMI Roadbed will stick to the dust and not the base. Use the strip of paper that separates one layer of the material from the other in the roll to press the AMI Roadbed firmly onto the sub-roadbed. I use a J-roller for that. Make sure to keep the roller parallel to the sub-roadbed otherwise the AMI Roadbed will not provide a level surface for the track (unless, of course, that is what you want). However, for a more permanent installation, the most effective method I have found is to use "Liquid Nails for Foamboard". Spread it thinly over the area where the AMI Roadbed will be installed, and place the Roadbed on it. Just finger-pressing it into place is sufficient. Using the J-roller won't work because the Roadbed will move around on the glue.
Roadbed
For the layout mentioned above, I laid out my track (Micro Engineering code 55 unweathered flextrack) on the AMI Roadbed. The track is just pushed down a bit, but not a whole lot. I used to use the J-roller to really work the track into the Roadbed, but the track had a tendency to get out of level due to the inevitable uneven pressure exerted on the roller. Just press the track down a bit enough to make it stay. Then rely on ballast to hold the track down to the AMI Roadbed. After laying the track, I shape the outside edge of the AMI Roadbed. At first I used a flat-head screwdriver (gleaned this technique from the Reid brothers as covered by Allen Keller's video tape mentioned above), but now I simply cut it with a #2 Exacto blade. The blade is flexible and makes it easy to shape the roadbed to fit the track. You can rest your hand on the track, which makes it very easy to stay close to the outside edge of the ties (as seen in this photo).
Roadbed
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Like a lot of model railroaders, I like the concept of trains that run quietly. That is, a layout that doesn't make the noise of the engines louder because of the hollow chamber effect of the area under the layout. At first, for my S-scale layout, I thought about using insulation styrofoam as the base of the layout. That didn't work out for two reasons. One, I tried a bunch of glues and none of them worked well. There is no air between two sheets of styrofoam so the glue, if it dries at all, takes "forever" to dry (we don't have 2-inch thick styrofoam in Houston, Texas). The second reason why I decided not to use styrofoam sheets for the layout base was that once I did manage to glue a couple of sheets together, they were not flat. Even though I took care to glue them on a flat surface, for some reason the glue must have pulled them at an angle. I put many weights on them while they cured. I finally decided to forget about styrofoam sheets as a layout/track base. I decided to go back to the old favorite, the cookie-cutter method for the sub-roadbed. My plan was to cover the sub-roadbed with cork. However, the only cork I could find was 3/32 of an inch thick. That was just too thin for my tastes for S-scale (works well for the smaller scales; I've used in on my N-scale layouts). Then one day I was wandering through Hobby Lobby when I saw Woodlands Scenics' Track-bed. The company makes it for N-, HO-, and O-scale, but not for S (of course!). As you can see, I decided on the O-scale version, with the intent of trimming it down to fit S-scale. The box contains a continuous roll of 24 feet of this lightweight foam. After I got it home, I measured it and its thickness comes out to about one scale foot in S. That is more what I had in mind for S-scale. The company makes other variations on this product. As far as price, I bought two boxes at a Hobby Lobby near us for $12.99 each and another one for $14.99 at another location. Both were running a sale of 40% off, so I was happy with that.
Roadbed
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Since I was back at dealing with foam, I had to once again face the issue of how to glue this foam to the painted MDF sub-roadbed. Woodland Scenics recommends their own Foam Tack Glue. Generally I find their products too expensive, but still, I checked Hobby Lobby and they didn't have the glue in stock. I spent some time doing research on the Web and found that many web sites referred to Pliobond. The advantage of that glue was that it should work with foam and that it is rubber-based, which means it adds to the sound absorption. I found a 1/2-pint container at my local Ace Hardware store for $6.99. I cut a piece of foam off and glued it (per the instructions) to a left-over piece of MDF. I put some weights on it and waited about 45 minutes. The results were promising. It had enough hold and it didn't eat away at the foam, but I could pull the foam off with some effort. I figured that with the larger sheets of foam on the sub-roadbed that it would work just fine. The downside was the incredible, horrible stench! This is the nastiest stuff I have ever used! I did use it to lay about 8 feet of the foam on my layout, but I just couldn't take it any more. Days later we could still smell it in the house. I threw it away. I will never use that product again! I highly recommend a respirator and using it only outdoors, if you have to use it at all.

I also tried Elmers wood glue, because I read on some websites where people had used that to glue foam. After 30 minutes of drying time, the foam pulled right off. That didn't work.

I went back to Lowe's to find some other glue. I had used PL Foam Board Adhesive when I tried to glue the layout base's insulation styrofoam sheets, but it just didn't work. It provides no initial tack, so the sheets moved around on me while I was trying to put weights on them. It took days to dry, and even then I could easily pull the sheets apart.

When I was at Lowe's I saw Loctite Power Grab Foamboard Adhesive (apparently no longer available). It was about a dollar more at $4.20, but it worked great. You get about 15 minutes of working time, so during that time you will need to hold the foam in place with pins and/or weights. After that time it is dry (I usually give it about 30 minutes). It does indeed provide quite a bit of initial tack. It takes a full 24 hours to fully cure. It doesn't eat at the foam, and it holds it in place after it dries. It only has a very faint, pleasant odor.

Update: After two weeks when I was laying ties on the foam, I discovered that the foam was coming loose from the sub-roadbed. I had tested the Loctite glue with a sample piece of foam and MDF before I started using this combination on the layout. The day after the test the foam was very solidly attached. I experienced the same thing on the actual layout. However, now, after two weeks, the foam could be easily pulled off of the MDF. I have, therefore, decided to abandon this method. I will now use ceiling tiles glued to the MDF sub-roadbed.

My message here is, if you are going to use some sort of foam for your roadbed, spend some time testing your actual set-up and give it time to cure to see if it really holds. I am never going to use foam again.
Roadbed
In the past I had read about people using ceiling tile for their roadbed. So I went to Lowe's and bought me a box of 1/2-inch ceiling tile for just under $11. It contains ten 12" by 12" tiles. The tile is made out of a man-made fiber. It should, therefore, provide some sound-absorption. There are various styles of ceiling tile, but the photo shows the one I bought, because it has a very smooth surface.
Roadbed
This is one of the tiles. It has a tongue-and-groove design so that each tile can be slid into the next one, thereby making a cohesive whole.
Roadbed
I had already cut (cookie-cutter style) my sub-roadbed base out of MDF boards. So, I snapped a handful of these ceiling tiles together on a flat workbench and laid my MDF sub-roadbed on top of them. I marked off the MDF on the tiles using a pencil. Next, I used a utility knife to carefully cut out the matching ceiling tiles. Each cut requires about four passes. After attaching the MDF sub-roadbed onto my layout, I glued the ceiling tiles onto the MDF using Elmers yellow carpenters glue. I took advantage of the tongue-and-groove system as can be seen in this photo. For experimentation, I glued a piece of scrap ceiling tile to a piece of scrap MDF using Elmers yellow carpenters glue and another test piece using Liquid Nails for Subfloors. Both provided an extremely secure glue joint. The Liquid Nails had a bit of an odor to it, so I chose to use the Elmers glue. Then I tested gluing a basswood tie to the top of the ceiling tile. I used both Elmers yellow carpenters glue and Matte Medium. Again, both created a very solid joint. I wasn't able to pull either off the tile.
Roadbed
The tile's surface is very smooth. However, I did need to deal with the V-groove left by the tongue-and-groove design. I filled it with Vinyl Spackling, which sets in just an hour or so. I followed that with a light sanding. To seal the ceiling tiles, I painted them with indoor latex paint. The ceiling tile generates a lot of dust if you even look at it funny, so keep a vacuum cleaner nearby.
Roadbed
After the track has been installed, it is easy to trim the roadbed's sloped profile into the ceiling tile (followed by another paint session to seal the new cuts. My conclusion is that it is indeed nice and quiet. This is my main way of building roadbed from now on.
Roadbed
I have even used ceiling tiles on a set of three modules I built for our club layout. Here you can see several full-size, painted, but un-trimmed ceiling tiles glued to the foam tops of the modules. These modules are very lightweight.
Roadbed