It took me a while. About a day. I had to scrape the entire underbody of lose rust and paint, which was mostly lose paint in certain areas. Then I had to knock all the loose rust from the rockers, then fill them with foam. [The professional way would be to take the plastic panels off and either replace the entire rocker(weld one in), or weld a patch panel in. I don't weld.] Then I washed the underbody down from dirt and stuff, I just used a wet rag with water only, and another rag to dry it. That way I didn't have to worry about leaving soap behind, and it got it clean. After it was dry and the foam dried, I cut the excess foam level to the rockers. Then I sprayed two coats while laying under the car. Not very good conditions to paint in, but you can still see what you're doing, it's just not comfortable. I had it on jackstands, front and rear to get it up as high as possible while still being safe. Then afterwards you don't want to drive in the rain/wet roads for at least 24 hours. Add more time if it's humid or cool out.
Always wear safety glasses, but an entire face shield would be best from all the falling rust.
