Jim, I was able to do it in N scale but it is a very tedious cleaning job. I used drywall compound since it cures slowly and is easily worked. I spread and smoothed the compound right over the track, level with the top of the rail. I then took a junk freight car and pushed it along the track after the compound skinned over or set up slightly. Drywall compound is easily worked with a damp sponge after it drys. I have not done it, but a friend told me later that if I had placed a thread on the inside of the rail, before I spead the compound, that cleaning the inside of the rail would have been easier. He did not say how you would keep the thread in place, something I will have to play with next time.