Hi Ron, I tried a concrete product from "Arizona Rock & Mineral " . The results were pretty much the same as using spackle or water putty. ALso I tried one time, "Quickret" cement in a tube for patching cracks. It would not spread correctly and did not work. But was does work is the Quickret' in the container. It has vinyl in it and smooths very easy. It can also be thinned and still gives very good results. Lowes, Home Depot have theses products.
You need to build 1/4" curb in the chosen length with balsa or basswood and fill with product.. Make sure you build a crown in the middle. No road especially concrete if flat.
There are so many methods and different materials used in model roads. I have tried just about all of them.. Here is a pic of Blacktop, concrete, and cement... I found that 1/8" cork also is very realistic and is the long portion of these samples...
This is all 1/8th" Fine cork. A very lite coating, in spots of vinyl spackle. Raw umber, "Pan Pastels, for weathering. Base coat of apple barrel "Blacktop" thinned out. That's it...
Finished product'
