This article refers to painting flextrack. I typically paint the track before I ballast. Most of the time I ballast before I have scenery in place. Most modeling books show ballasting after the scenery is in place, but I rely on the ballasting process to hold the track down to the AMI Roadbed. I don't use nails or spikes.
The track painting method I use I learned from Allen Keller's video tape covering Monroe Stewart's layout. Painting track by hand with a small brush is fine for about a foot or so, but it is too tedious to do for extended periods of time.
I spray-paint the track with two colors, flat brown and flat black. The brown is a cheap 97 cent spray can I bought at K-Mart (I believe). It is called "Fresh & Easy" spray enamel and the color is "FE509 Brown Primer". The black color is called "1602 Ultra Flat Black" by Krylon (probably bought at Walmart or Lowe's). Really, any rust-like brown and flat black will do.
The track being painted for this article is a return loop that encircles a future mountain on my third layout. The track is attached to the AMI roadbed, and the wiring is complete. I covered any area that does not need to be sprayed. You can pretty much assume the spray to go everywhere, because it does. I have sprayed on one side of the room, only to find the dust on the other side of the room. I also use painters masking tape to cover track or other items that shouldn't get painted.
Before spray painting the track, I grab a household lubrication oil and put a dab on my finger. I run my finger over the top of the rail so that a thin coat of oil covers the rail head. This makes removing the spray paint from the rail almost trivial later on. Without this step, you'll spend a lot of time rubbing the paint off of the rail.
I spray a short section of track (usually do no more than two feet) with the brown color. This is my base color so it needs to cover all of the rail side. I spray it at a low angle to the track so that most of the spray hits the side of the rail. I spray only those sides that are visible from within the layout room.
Immediately clean the rail head! I recommend having the tools right beside you. The longer you wait with cleaning the rail heads, the harder it is to clean them. That is why I only do a short section at a time. With the oil, cleaning is easy. I use an eraser (or a Bright Boy) and wrap it in a piece of paper towel. The eraser provides a smooth flat surface and the paper towel picks up the paint. Thoroughly check the rail head to make sure they are indeed clean (one wipe of the paper towel should be all that is necessary, if the oil was nicely distributed). I usually finish painting all the track with the brown color first before moving on. I then cover the railhead with oil again.
Next, I spray the black paint. I want to use the black as more of a highlight color. This particular black spray paint is very aggressive and tends to lay down a thick layer. So I only barely touch the nozzle of the can to let just a bit of paint out every so often. I don't cover all the track, just an occasional dab here and there. Again spraying from the side. Once the ballast and scenery around the track is in place, the black highlights represent oil or grease spills. I then clean the track and remove the masking tape, plastic, and other materials used to cover the surrounding areas.