Bridge Abutments

By Ty’s Model Railroad - 11/06/2011 04:42:00 PM

Single plaster bridge abutment made from plaster of paris with carved brick pattern in its face

I’ve been avoiding the construction of the abutments for my trestle and bridge for a while, mostly because I didn’t have the slightest idea of how I was going to construct them. I am now at the point where I cannot continue my layout terrain without the abutments being in place. I knew I wanted the abutments to have a brick look, so I started to do some research on how to accomplish this. I found two options; the first to use brick textured styrene and the second was to cast the abutments in plaster. I opted with the latter option, mainly due to cost and availability.

5 cardboard bridge abutment templates numbered 1 through 5 laying on newsprint

I first started by making a cardboard template of each abutment to ensure that it fit properly on the layout. I notated on each template the front and back so I didn’t mix them up. I used each template to create a basic form out of heavy cardstock and masking tape, ensuring that the face of the mold was level and flat. It's important to remember that the form needs to be built in the REVERSE direction of the front of your structure. In other words, the template needs to be mirrored and should lay in the form back-side facing up. This is a mistake that I narrowly avoided, which would have resulted in backwards abutments.

Cardboard bridge abutment template beside a matching cardstock plaster mold

I used plaster of Paris for the castings, mixing it until smooth. I then quickly filled the form to about 1/2" thick, shaking the form to evenly settle the plaster. While the plaster set, I butted books up against each edge of the form to prevent the form’s walls from bowing outward. Cardstock worked fine for this type of casting, as long as the plaster wasn’t too wet which would warp and tear the form.

Single plaster bridge abutment made from plaster of paris

After the casting set for about 10-15 minutes, I gently tore away the paper form. I then smoothed out and rough edges, which were most apparent on the back side. At this point the plaster was solid, but still wet enough to carve. I used a ruler and a scissor blade to carve the brick pattern. After the cast was a little more firm, I etched cracks and gouges in the bricks to make them look a bit more weathered. I then gave the abutment a final brush with a firm nylon brush which gave the plaster some texture while removing any loose plaster pieces.

Single plaster bridge abutment made from plaster of paris with carved brick pattern in its face

Because plaster of Paris has such a fast setting time and thus a very short window to work with, I only cast and carved one abutment at a time. If I had even poured two at the same time, the second would be too hard to carve by the time I finished the first.

Five completed custom plaster bridge abutments displayed together on newsprint

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