Wall murals for exterior walls take a good bit of time and effort, but the basic process is relatively simple. By starting with a small design and expanding it to fill your outside wall, you can create an outline that can be filled in by almost anyone, or by many people working together.
Prepare the outside wall for a wall mural. Use a paint scraper to remove any obvious flaking paint. Wash the wall thoroughly. If any existing paint coverage is latex-based, no further preparation is required. If the existing layer is oil-based or of unknown origin, use a household abrasive cleaner to clean and roughen the wall. For untreated brick or other masonry wall, paint the surface with masonry conditioner (a specialised type of primer) and allow to dry.
Roughly measure the dimensions in feet of the outside wall on which you want to place a mural.
Convert the size in feet to an equivalent size in inches, and use the ruler to draw a rectangle this size on paper. For example, if your outside wall space is 6 feet by 8 feet, draw a rectangle 6 inches by 8 inches.
Draw an image you would like for your wall mural into this rectangle.
Draw a grid of 1-inch squares over your template. You can do this by making marks an inch apart along each side of the rectangle, then connecting parallel marks.
Use the yardstick, chalk and the same method to draw an equivalent grid of squares outside where you want to do the wall murals. These squares should have 1-foot rather than 1-inch sides.
Transfer the small design to the outdoor wall using chalk and the squares as guides. Copy the image inside each square individually. For example, notice if the lower left square has a diagonal line from one corner to the other or a small circle in the lower half. Try to copy these marks onto the outside wall accurately as possible.
Look at the whole image when you're finished and smooth the lines out if there's a lot of distortion around the borders of the squares.
Fill in the wall mural shapes you've drawn in chalk, using colourful exterior house paint and large brushes. Any exterior wall paint will do in a pinch, but some will be far more durable than others. Acrylic exterior paints are ideal, especially for brick or other masonry surfaces.
Consider adding a coat of artist-quality acrylic varnish to the entire mural, particularly if you want it to be a graffiti-resistant washable surface.
Wall murals can use a lot of house paint, so they're a useful way to use up the bottoms of any old cans you have sitting around. Just be sure to consider your colour options when planning your mural design.