The big box stores sell different types of mud. There is the regular drywall mud and there is the lightweight mud. I've been using the regular mud for the tape and first two coats but I haven't really seen much of an advantage with the lightweight mud. In fact there is a big disadvantage, it is more expensive and instead of 4 gallons it is only 3 1/2 gallons, and it seems that once I clean the seam up and go to reuse the lightweight mud, it seems just like the regular drywall mud. So, do you guys that do this on a regular basis use the lightweight mud at all?