Thanks for the comments. I just used the craft foam from Michael’s. I think it’s 2mm which is a little thick for HO. I haven’t been able to find 1mm locally, but I’ve seen it offered on the internet. You could always bevel the edge of the 2mm or just cut it narrow enough that it doesn’t interfere with the flanges. But one of the reasons I tried the foam instead of something rigid is that I wanted it to go the full width of the track without any flangeways. I tried paper with a texture printed on it. It would work well for N scale, but for HO it might be obvious that it’s paper. Perhaps you could use a textured paper that would give it some depth.
For the small cracks, I tried heating a straight pin in a candle flame and drawing in the cracks. The problem is that it looked like it was drawn by hand. It’s difficult to make something look random.
I don’t think the crackle finish worked because I sponged the paint on rather brushing it. I think you need to brush the paint on pretty thick to get it too crackle, but I didn’t want the paint that thick. I wanted the black foam to show through.
BTW, here’s how the big boys keep asphalt away from the switch.
Steve S