As long as you plan for the type of bridge that you intend to use, either way will work. Most of my bridges were built after the rough scenery was in place. I used patching plaster over screen for scenery, but created my own set of problems - not related to the scenery-making method. Most of my mainline track is on 3/4" plywood roadbed, and it was built continuously around the layout, even where bridges were eventually intended to go. I used the roadbed as a pattern for the bridges, as all of mine have some sort of a curve or curves in them. When I was ready to build and add-in a bridge, the corresponding roadbed was cut out with a jigsaw.
For this bridge over the Maitland River, I built the bridge to follow the curves of the roadbed, then cast the piers and abutments in patching plaster. This bridge was the only one installed before the scenic plaster landforms were in place, so the piers and abutments could all sit on the flat plywood surface of the unfinished riverbed. The tops of them had to be cast to accept the various types of spans making-up the bridge, and after painting, they were glued in place with carpenter's glue. The finished bridge was then plopped into place. The bridge, all one piece, is removeable, so it was relatively easy to finish the scenery and "water" when I was ready.
This next bridge was a similar situation, except that the plaster landforms were already in place. The main difference in placing the bridge was that the bottoms of the cast abutments at either end had to be carved to fit the contours of the river banks.
The three spans are, again, all one piece and removeable, so it was easy to go back later to add the trees and water.
The lower bridge in the foreground was similar to the previous one in installation and is also removeable and one-piece. Both abutments and all but one of the piers had to have their bottom surface carved to suit the terrain.
The high bridge in the background is also removeable and one-piece, but because of the support structure (i.e. not monolithic), posed some problems.
Because the scenery was already roughed in, I cast footings of various heights to suit each leg of each tower, then had to carve the bottom of each to match the terrain. Each footing was drilled out to accept a short length of 1/16" music wire, which was ca'd in place, then each tower leg's base was drilled with a corresponding hole - this allows the bridge to be removeable and also keeps it properly aligned and stable. The large, cast abutments at either end of the span had to be carved to fit the high points and contours of the terrain, then more scenic plaster was applied and the abutments "squished" into place. Any excess plaster was cleaned-up before it set.
The uppermost bridge, also one-piece and removeable, was similar to the one shown just previously, with the difference that the footings and abutments were made with .060" sheet styrene.
The abutments were built with sheets, much as you would build a structure, then the bottom edges were carved to suit the terrain. After wetting the area slightly, more plaster was added to provide a soft base, then the abutments were pressed into place. More plaster was also placed inside the abutments, to give them greater strength and stability.
The footings were made by stacking appropriately sized squares of .060" styrene, until the required height was achieved, then the top edges were bevelled and the bottom faces carved to match the terrain. They were first set in a bed of soft plaster, which was then worked up around each footing to hold it in place. All had a piece of music wire inserted, as with the previous bridge.
All of the extra work for the last two bridges could have been avoided if I had planned out the bridges before doing the scenery. I then could have made a large, flat platform under the spot where each tower was to be located. This would've allowed all of the legs on each tower to be the same height, and all of the footings of all towers to be the same size. I could've also made suitable platforms to support the abutments at each end of the bridges, simplifying the casting process.
So, if you plan ahead, you can do either scenery or bridges first.
:-D:-D
Wayne
