Spray the back of your chosen stencil with adhesive spray. Position it on the chosen area of the wall. If you are using a large-production stencil, start in the middle of the most visible wall at the ceiling line. Press the stencil down to get the best adhesion.
Mark the stencil registrations onto a piece of masking tape placed under the stencil. Use a watercolor pencil that you can wash off when finished.
Apply Venetian plaster or drywall plaster to your drywall blade with a putty knife. Apply a thin coat of plaster to the opening of the stencil. Don't worry if you get plaster on the edges of the stencil opening.
Smooth the plaster with your drywall blade or putty knife while it is still wet. Press a damp sea sponge gently into the wet plaster if you want a stone-like quality. Allow the plaster to dry according to the manufacturer's directions.
Scrape the plaster off the stencil after every three or four applications. It's important to keep the stencil lines clean for best results.
Sand the nibs, or raised bumps, off the dried plaster designs, using a sanding block.
Paint over the stencils in the same color as your wall for a subtle effect, or leave them white for more drama.