For coarse-grained particle-based simulation methodologies such as our chemically-specific DPD models, there are two approaches to modelling walls. The first is simply to extend the particle-based paradigm to represent a wall as an array of DPD beads which are either 'frozen', or tethered to fixed sites. In this, one can take advantage of the bead-bead interactions already derived within a standard parametrisation strategy, but on the other hand the determination of the surface energies may be delicate. Additionally, there is the need to choose the density and arrangement of the beads, and parametrise the tethering force if the beads are not frozen. Such an approach could however be suitable for materials which are chemically patterned or have nanoscale roughness. An alternative approach, which is the focus here, is to model the surface as a smooth, featureless substrate. This approach is suitable for atomistically or molecularly smooth materials, such as glass (silica), many plastics (for example, polythene, polypropylene, polyester), minerals (calcite, hydroxyapatite, etc), organic crystals such as sugars (sucrose), and perhaps even ice. Within this approach, which pertains to many situations of direct practical relevance, the parametrisation problem becomes simply one of designating the wall forces for each bead type in the bulk. Moreover, determination of the surface energies is very straightforward as we shall see.