Before starting on my actual layout, I’m doing a bit of a diorama to experiment with things. One thing I tried was the trick of using unsplit N scale cork to simulate the lower ballast of a siding (I model in HO). I shimmed the N scale cork with some cardstock, and as soon as the glue dries I will sand it all to make the transition nice and smooth and gradual. Frankly, though, I am not pleased with the appearance, although I suspect it will look better once the track is in place and everything is covered with ballast.
I’m open to suggestions. One thought I had was to just use all HO scale roadbed, and sand down the sidings - I shudder to think at the idea of using a sanding block and trying to evenly sand down a 10 foot passing siding, although I DO have a small hand-held orbital sander (1/4 sheet size) that would make the job a bit easier.
Check California road beds. The make homasote bed in a mainline and branchline height. They also offer transition pieces to go from one to the other. I used it and like the look. http://calroadbed.com/Products.aspx
I have used 1/8 in balsa sheet for transitions. It sands better than cork and it about the same thickness as N scale cork, about 1/2 the thickness of HO scale cork. Its cheap and readily available.
I use styrene to shim and also have used adhesive for foam projects let the track find its own down grade and then caulk a little bead under it both methods look the same after ballast is layed.
I use Homabed, now made by California Roadbed Co. Before this company starting making 1/8"-high HO roadbed, I used 1/8" gasket cork (from a True-Value hardware outlet) to make a lower roadbed for sidings. The first transitions I used were sections of cedar shingles sold by the original Homabed company, but I’ve since found it simpler to sand the full-height (.24") roadbed to form transitions to the sidings. I do this with the sanding block in one hand and the Shop Vac hose in the other, and that only takes a couple minutes and leaves no mess to clean up.
I cut the gasket cork in strips about 4 scale feet wide for use with 8-foot ties and glue down a pair of strips for each track just like regular cork roadbed. I leave the edges square and let the ballast form its own slope. This cork is denser than the usual cork roadbed, which makes it a better support for my handlaid track.
I have used N and HO scale Woodland Scenics foam roadbed to represent “branch line” lower roadbed–it is typically compressible enough that one can simply pin the track in place over it and it “gives” enough to produce an incline. With ballast glued in place the track is securely held in place and the roadbed stays firm.
I don’t know if it is still made, but a few years ago I picked up some thin cork roadbed. I think it was made by Lifelike. It was too thin for the mainline, but since I bought it at Toys R Us it was cheap enough that I doubled it for the mainline.