The pros know the secret to a level surface is using guide coat while you are block sanding. A light misting of guide coat over you primer will show you low and uneven areas, keep sanding and applying guide coat until the guide coat disappears, its that simple. Use Black Guide Coat over gray and tan primers. Use Tan Guide Coat over black primers. Eastwood is the ONLY company to make guide coat in tan. One aerosol covers about 30 square feet of surface.