Stone Arch Viaduct / Bridge

[doctorwayne]

So a lot of the brick facings on your buildings are printed paper glued onto the sheet styrene?

The first of the last two in my post, above, is, and there are quite a few of them on the layout.  Some are simply two dimensional "flats", while many have some depth, like this one (ignore the curve at the eaves - imparted by the camera's lense)...





This one has some short side walls, too, but looks only so-so in this view...



...and less-so here...



...and this one pretty-much finishes it off...



These two have about an inch of side wall depth , but there'll eventually be three-dimensional structures in the foreground...



These two are basically "flats", with their depth only that of the .060" sheet on which they're mounted, plus  the 1/8"x1/8" stiffeners cemented to the back....





Unfortunately, those background structures are no longer available.

But, to answer the un-asked portion of your question above - yes, if your viaduct isn't going to be right up front to viewers, then you can likely do a very convincing stone "veneer" using printed paper.

For the first batches of those flats, I used contact cement to affix the paper to the styrene (it helps to first "prep" the styrene with some brushed-on solvent - I used MEK, which I also use as a cement for styrene.  Such prepping makes applying the gelled contact cement easier, and gives a better bond because the styrene otherwise draws too much of the solvent out of the contact cement, making it difficult to spread.  (I use a 2" brush for this work.) 
The back of the paper also requires a coat of contact cement, and you need to let it dry the for at least the amount of time noted on the can. 
To get good alignment of the paper on the styrene backing, lay a sheet of waxed paper over the dried cement on the styrene, then place the paper atop it.  Jockey the paper around as needed, then move the waxed paper slightly so that a sliver of the bottom and one side of the styrene are exposed.  Next, align the paper with both of the respective exposed edges of the styrene and very carefully press down to secure the paper in alignment with the backing. 
You can then begin to slide the waxed paper from between the two surfaces, following along with your free hand to smooth the paper onto the styrene.

Later, I experimented by using the same 2" brush to apply a liberal amount of MEK (it evapourates rather quickly) to the styrene, then simply placed the paper atop it while the MEK is still wet, smoothing it from the application side and across the full width. 
While this can be quicker than the contact cement method, you need to work while the MEK is still wet, but not pooled - too much MEK can soak through the paper and mar the printed image.  Also, you can't use the waxed paper method for protection while you align things. 
While I generally had good results, I also did some where the sheet of styrene backing was cut only to a rough size, allowing the paper image to be placed within its edges, then used a utility knife to trim the backing to-size.  Images that don't have sidewalls of any appreciable depth (the thickness of the backing and its associated bracing) should be painted a suitable colour that won't attract the eye of viewers.

Wayne