I used Hydrocal, and as long as you are careful to cover all part of the layout yaround where you are working, your roads will come out fine.
you first have to use something like WS's paving tape, then quickly pour down the hydrocal, and make it as flat anf even as you can. focuse on sperading out as much as you can in the most even you can manage before the hydrocal starts setting.
If the road surface is alittle too bumpy, you can use a big trough ( is that the name for it? its like a big spackeling thing), hold it at an angle, and drag it to you. It will start scraping up all the bumps, and will leave an extremely smooth surface.
at this point, you can use sand paper to rough it up, or use WS's Top coat, which does a great job of recreating asphault. the paint has course pigments, and it makes the road feel rough. I found that if you want to make the road look grayer and weathered, you could take some crumbled Hydrocal that may have dried in your container and turn it into powder, then rub it into the roads with your fingers. It will will stick to the road without any kind of sealing finish.
Its time consuming, and kinda frsutrating, but it works.