Door frames, window frames, baseboards, corner mouldings, etc are trimmed with solid wood, eg oak, trim pieces. The trim pieces are fitted over splines which are screwed to the wall. A jig enables the splines to be located accurately in position. The spline includes no beads, snaps, or other features that would require the oak trim section to flex; instead, the trim is secured by the friction arising from the fit of the spline into a groove cut into the rear face of the trim section. In a variation, a pair of parallel grooves are provided, together with a corresponding pair of splines, which are mounted on a web.