Tuesday, December 27, 2011

Hardshell Terrain

For my terrain structure, I opted to use the hard-shell method, consisting of cardboard strips, plaster infused paper towels, and a final layer of plaster. This seemed to be a popular, tried and tested method, and though messy, the materials are very cheap and the end results are very effective.

Cardboard strips to support hard shell terrainCardboard strips to support hard shell terrain

I first started by cutting several different length strips from a cardboard box, all between ½ and 1 inch wide. The strips were then bent to the desired curvature and fastened to the benchwork with either white glue or staples, or a combination of both. I spaced each strip about 1 inch apart. For most of the strips, I didn’t require horizontal support strips, except where the vertical strips were longer and tended to sag a bit more. Crumpled newsprint under the strips also helped with support in some areas.

Cardboard strips and crumples paper for hard shell terrainCardboard strips to support hard shell terrain

At this point, I also incorporated some crock croppings that I had cast with plaster earlier. For the more rugged looking terrain features, I used the same crumpled paper method that I used for my mountain tunnel. For future planned roads, I simply cut a desired sized piece of cardboard and attached it just as I did with the other strips, ensuring a smooth grade from the upper level to the lower ground level.

Paper towel strips soaked in plasterPaper towel strips soaked in plaster

The next step was to cover the cardboard strips with plaster-impregnated paper towels. For this, I first tore sheets of paper towel into strips at various widths. Make sure you have a good mixture of thin and wide strips, as it’s a lot easier to cover a large area with wide strips then several small thin strips, and vice-versa for small areas.

Paper towel strips soaked in plasterPaper towel strips soaked in plaster

I mixed powder drywall compound into a large, shallow container with water. This took a little trial and error to get the right consistency; if too thin the paper towel strips will dry and peel, and have no rigidity. If too thick, the paper towel will just rip under the weight. I found a consistency of oatmeal worked best. Good quality paper towel also helps immensely. I had to keep stirring the plaster mixture as I went, as the plaster tended to settle to the bottom of the container. Adding a bit of water to the mixture as I worked will also keep things flowing.

Paper towel strips soaked in plasterPaper towel strips soaked in plaster

Once I had found the proper plaster mixture, I dipped each strip of paper towel into the mixture, wiping off the majority of excess plaster from the strips with my fingers. I then positions the paper towel strips horizontally across the cardboard strips, overlapping them for added strength. I didn’t worry too much if the paper towel strips sagged a bit between the cardboard support strips as this would be leveled off later with the final plaster layer. I used my fingers to smooth the strips as much as possible.

Final plaster layer of hard shell terrain width=Plaster retaining wall cast in place

After 24 hours the paper towel shell was dry, and I was left with a rigid but brittle shell. The final step was to cover everything with a final coat of plaster, which greatly strengthens the shell, and smoothes out the unsightly seams of the paper towels. I used a gypsum based plaster, but made the mistake of using a pre-mixed product, which is way more prone to cracking and shrinking then dry mix, and resulted in filling in a lot of cracks. I also cast a retaining wall (as seen above) using a paper mold that I made directly on the layout. The wall is cast with plaster of paris, and finished with hand carved bricks.

Final plaster layer of hard shell terrainFinal plaster layer of hard shell terrain

I spread a thin layer of plaster over all of the paper towel shell, thicker in some areas to eliminate low spots. I blended in all of the rock croppings and filled in any holes/joints, etc. I used a combination of my hands and small plastic spatulas to smooth and level the plaster layer and blend it with the existing bridge abutments and terrain. The ground foam and dirt/ballast that I will add later will fill in and deficiencies in the plaster. I still have a few touchups to do, but I can safely say that the plaster hard-shell is finally complete.