Hi Carla! I see you're from my neck of the woods. :)
I used acrylic patio paints on this and it looked great for about 4 years. It did fade eventually because it was facing west, but the homeowners loved it - they felt it made it look like an old structure.
:) I have also used regular quality acrylics on exterior murals (delta ceramcoat is one) but never use cheap paint because it's watered down.
