I was told by a painter that it's not a primer. The label says it doesn't need to be sealed prior to topcoat. It's like a sprayable filler to remove minor imperfections. Once I block it I will prime then block with 400. It's cheaper than primer and metal glaze. It applies evenly minimizing sanding. It is thick and requires a 2.0 gun tip. It can be thinned a little like I had to do tonight due to being 55 degrees.