Applying filler to different substrates Applying roller filler to joints Start by inspecting the execution of the joints and the plasterboard. Follow National guidelines when finishing plasterboard joints. Roll the filler into the joint with a 10 cm roller on a extension pole, or apply the joint filler by hand. Embed the paper tape with the outside of the roll facing the wall. Press it in and apply a light coat of filler on top so that the whole tape is bedded in, but is clearly visible under the filler. Apply filler to the edges, trimming the filler to level the edges and avoid ridges. When the filler has dried, apply filler to the joint covered by tape to a width of 25 cm the first time, and to at least 35 cm the second time. Apply filler to screw heads. Sand when the filler has dried. Fine smoothing is recommended on walls with raking light. Then sand.