Thanks for the compliments, 4railsman. For those parts of the walls that are fixed in place (not many actually!), I tend to use PVA glue, undiluted. My most common branded one is Aquadhere. Some parts of the walling are still loose (or held in place with nothing more than a few spots of Blu-tack) because they are not yet in their final positions; most only need minor tweaks to their locations. The walls near the tunnel mouth where most of my photos are taken are resin castings of unknown provenance, bought from a local swap meet. The bridge supports are wood (pine) with Vollmer embossed card brickwork glued on with PVA. I use the N scale brickwork as the HO scale stuff seems oversized to me. The filled arches on the other side of the bridge, opposite the platform came from International Models, alas no more, and are also glued in place with PVA, apart from the bit adjacent to the overbridge, as that needs a little adjustment too. At the other end of the layout, none of the walls are glued in place, and some are merely placeholders until I get the final pattern walling in place.