How to Build an Exterior Fresco

Design and Planning

• Before you begin to construct your fresco wall, select a design and plan the dimensions of the finished mural. Floral patterns and nature scenes are common fresco subjects, though your exterior fresco can depict any image you choose. Purchase paints or pigments beforehand, since the painting process requires you to work within a limited amount of time. Frescoes require paint to be applied to slightly wet plaster, so construct a temporary shelter with a tarp or choose an area where your wall will be protected from rain and direct sunlight as you work.

Plaster

• Preparing for an exterior fresco involves producing a plaster wall in an outdoor location. The wall may be a freestanding structure that blocks wind and provides privacy or a portion of your home's exterior that you select for the fresco treatment. Mix up a lime-based plaster using water and sand or a prepared dry mix. Spread the wet plaster evenly using a trowel or knife, according to the plaster manufacturer's directions.

Painting

• Once the plaster begins to dry, you have several hours to paint your fresco. If you have a template of your design, stencil it into the wet surface using charcoal. Even if you want to work freehand, produce a quick sketch in charcoal to serve as a guide. If you're working with ground pigment, add water and rubbing alcohol to produce a liquid with which to paint. Otherwise, use fresco paint directly from the tube or after mixing it on any nonporous surface such as a plastic palette, bowl or sheet of scrap metal.

Finishing

• Once the plaster and paint are completely dry, you can seal your fresco for added protection outdoors. A sealer is especially important if you build your fresco where it will receive direct sunlight or use colors that are subject to fading, such as bright primary colors. Use a transparent sealant designed for use on plaster or stucco. Apply it in layers with a brush or roller to seal in the color and enhance your fresco's durability regardless of the climate.