If you use polystyrene for building scenery on your layout, then you will probably end up with lots of scraps after you have finished shaping the hills and cuttings with your craft knife or hot wire. What to do with the stuff? The very small bits cling to everything while the larger scraps are usually too small to be useful. Here is what I do.
Cleaning out the kitchen cupboards one day I discovered a French made Moulinex electric mincer which my wife used when the children were young. Previously, I had tried an ordinary mincer to cut up the polystyrene with no success. The corkscrew blades on the revolving spindle were not sharp enough to cut the polystyrene, but simply squashed it. They were really only for pushing the meat, onions and so on, through the various sized holes in the different attachments to make the mince. This one, however, had revolving knives which should cut the polystyrene no trouble I thought. Nothing venture, nothing gain, I assembled the parts, switched on and fed some scraps of polystyrene in. What a mess! Minced polystyrene came out all right but not exactly into the ice cream container I had placed under the outlet opening. It stuck to everything, my hands, my jersey, the bench and the mincer. What was needed was a plastic bag to catch everything as it was discharged. So a plastic bag was attached to the outlet opening with a rubber band. This did the trick and in no time I had a bag full of minced polystyrene. There were still a few bits that escaped the bag but nothing that could not be cleaned up afterwards with a dustbuster or similar small vacuum cleaner. If you keep a dustbuster especially for the model room, and for this purpose, you can reclaim the bits of polystyrene from it and use them as well. The dustbuster can also be used for gathering up scenic materials, ballast and similar materials — but keep it clean. Now what to do with the stuff! Some plaster, a dash of PVA glue, water and a few spoonfuls of ‘mince’ into the mixing bowl. Stir well and apply the mixture to the cliff face. The texture was just what I wanted, better than plain plaster and no need for any fancy carving or crumpled tinfoil pressed into the wet plaster. And it was much lighter than solid plaster too. You probably don’t use as much plaster either which is another saving. You may need to experiment a little to get the right quantity of minced polystyrene in the mix for the effect you want to achieve, and a little more water is usually needed because of the absorbent nature of the polystyrene. But it is a way of using up small scraps of polystyrene and achieving a texture on otherwise plain plaster. The only thing left to do is the carry on with your usual method of painting and planting weeds, shrubs, undergrowth, trees, rubbish, or whatever else you want to add. Now, and don’t let the kitchen culinary manager read this, you can probably use an ordinary food processor to do the same job as my Moulinex mincer. It works on the same principle with revolving knives to cut up the ingredients. The chopping up of the polystyrene probably won’t do the food processor much harm and nobody will never know it has been used for this purpose if you give it a good cleanup afterwards.
Many problems arise when using polystyrene blocks to build up scenery on a layout. The biggest is how to shape it without creating lots of sawdust, which clings to everything including tools and clothes. After you have built up the blocks to the desired height using PVA glue, wait until the glue sets and use a fine hacksaw blade, hand-held at both ends, cut the polystyrene to the desired shape. The fine blades can be easily flexed to shape either convex or concave curves and the final surface is very smooth. There is also a very nearly complete absence of dust or tearing using this method. The surface is then finished by coating with plaster dipped paper towels.