If you are talking about painting the outside walls of a building, then we already told you what the problem is.
When you create a building in Maplet, you will start with a solid universe. You will then carve some rooms etc, but they all have only one wall surface, the inner face. If you want your house with solid walls that can be seen and painted from outside, you need to carve a huge block in maplet first, then add walls in the boolen addition mode, instead of carving rooms. Basicly this method is even more natural, building a house from the basement, wall for wall, ceil for ceil. Although it may be a bit harder to handle Maplet this way. You'll also need to use the transparent GUI mode etc.
If I completely misunderstood your question and you was talking about painting an outdoor scene, like a terrain mesh, rocks and hills etc., then I can only suggest to try if it works. Automapping may not work perfectly sometimes.
When you create a building in Maplet, you will start with a solid universe. You will then carve some rooms etc, but they all have only one wall surface, the inner face. If you want your house with solid walls that can be seen and painted from outside, you need to carve a huge block in maplet first, then add walls in the boolen addition mode, instead of carving rooms. Basicly this method is even more natural, building a house from the basement, wall for wall, ceil for ceil. Although it may be a bit harder to handle Maplet this way. You'll also need to use the transparent GUI mode etc.
If I completely misunderstood your question and you was talking about painting an outdoor scene, like a terrain mesh, rocks and hills etc., then I can only suggest to try if it works. Automapping may not work perfectly sometimes.