morairamike said "My track is laid on pre-ballasted foam. Now, yes, I thought it would degenerate but it is now 4½ years old and still fine. The shoulders are loose ballast laid with ballast glue, a kind of PVA." I have attached a couple of photo's showing part of my layout laid in this way. In this case, the underlay is the Peco variety which, in my experience, is not as long lasting as the Hornby product. Regarding morairmike's concerns re. the disintegration or "failure" of the underlay, I wold like to add that this part of my layout was built in 1993 and the ballast is still fine. However, I admit that were I to lift the track the underlay would probably fall apart in my hands.