It must be a sealed surface that is reasonably smooth. For example if it is a flat rendered wall, ideally the final coat of render would be smooth and have a few coats of primer/sealer and acrylic exterior paint.
About Jacqueline Hill
Multi-award winning artist who paints in all mediums and many different styles. Jacqueline teaches art classes in the Art School inside her own gallery. She is one of the leading portrait artists in Brisbane and is known for her pet portraits and Australian art depicting nature and wildlife. Her peaceful Brisbane art gallery and studio, Art at Heart, is nestled in the leafy bushland of the Western suburbs. See her art online at www.shop.artatheart.com.au