Recently we looked at the tactile quality of canvas or rough surfaced illustration board. But machine-made background textures can get a bit monotonous on their own. You can customize the surface by “pretexturing” before going into the final painting. Even if you work fairly thinly in oil in the final stages, it will appear to have lots of “impasto,” or rough painterly surface.
In the case of this image “Thermala: Alpine Hideaway” (page 76), I pretextured the entire board after the finished drawing was sealed with workable fixative and matte acrylic medium. To do this, you can use a mixture of modeling paste and matte medium (both acrylic based, and both fairly transparent). Brush this over the entire surface. The texture doesn't have to follow the details of the drawing very closely.
A good general rule is to build more impasto texture in the foreground areas and the light areas. Shadows and faraway misty regions tend to look better with a smoother surface.
Paint Texture Series
Paint Texture, Part 1
Paint Texture, Part 2
Paint Texture, Part 3