http://www.enrichpro.com/en/richdirt/index.html

Do you want to render more realistic facades ? RichDirt ® is a fast and easy way to enRich your renderings by adding simple and advanced dirt effects and give them a dramatically real look. Now you can age your 3D surfaces and give them a stained real look just the way dust, rain and water flows affect the look of actual buildings.
Do you want to spend less time ? Apply the desired effects on wall edges, windows and even the thinnest objects such as tiles and bring them to life. Impress with never before seen quickly generated dirt effects that you can easily control with a few clicks. RichDirt ® works for 3ds Max with V-Ray and Scanline.