Painting foam

Pink or blue extruded foam insulation has become popular for model railroads: lightweight, fairly rigid, easy to shape. Following Free-mo N suggestions, my layout modules were to be covered with 2" of foam. I bought a 4' x 8' x 2" sheet at my local home improvement store (the greatest advantage of living outside of California is that such foam is once again readily available). I found that the sheet would not fit in our minivan (at least, not without removing several child car seats to allow the van seats to be dropped down), so it was back to the store for a saw. Fortunately, the foam I got was scored on its center line, so deepening the cut and then snapping the foam went well.

Many model railroads spend an extended time in the "Plywood Pacific" stage: track down, railroad operational, but no scenery, just the wood/foam/homasote/etc. supporting the track. Since I'll be doing winter scenery, I thought that I could paint the foam white before track laying: far from finished scenery, but less jarring to the eye than bright pink during the Plywood Pacific stage. I thought that I could just quickly spray the foam with white spray paint before using it.

I knew that foam was sensitive to various chemicals, thus the common advice in the model railroad press to use foam-safe adhesives. So I was careful to buy spray paint intended for plastics, even noting that polystyrene is listed on the label as one of the plastics it was safe for. A few seconds after starting to spray the foam, it became apparent that the paint might be great for plastics, but not this foam. The foam kept bubbling and was gradually being eaten away. I wiped off the paint. You can see the results below (zoom in on the right). Basic moral: use acrylics/latex. Less noxious and won't eat your benchwork.

Just say no.