According to the Behr website, Behr's Venetian Plaster can be spread over a surface using a 4-inch trowel. Before spreading the plaster coat, smoothly round the trowel's edges with 100-grit sandpaper to avoid creating edge marks from the trowel in the plaster surface. Load the trowel top with the Behr plaster, and spread it across a surface using short and long strokes.
The Behr website states that proper plaster application requires that some of the original wall color peeks through the plaster slightly. Randomly make the strokes that apply the plaster to add depth and texture to the look. For best results, hold the trowel against the surface at a 15- to 30-degree angle. Wipe the trowel clear of plaster residue regularly during the application process to prevent older, drying plaster on the trowel from making scratch marks in the new layer of plaster.
After completely covering the surface with the plaster, Behr suggests waiting 4 hours for the first layer to dry and then applying a second layer of plaster on top. Place the second layer over the first using overlapping strokes from the trowel, with the trowel held between 30 to 60 degrees against the surface. The length of the strokes should vary randomly until the entire surface is covered.