At this point we'd filled all the major flaws in the raw glass with the spray filler and catalyzed spot filler. We then put the PPG K-38 primer/surfacer to the test. One good coat filled everything the spray filler couldn't work into fully. We went through yet another buildup/block sanding processes to get the job done just right. Incidentally, make note that all primers, and especially polyester primers, require a good, full cure between coats. Whenever possible, give the finish either 1) time, 2) sunlight, 3) an oven-finish, 4) infrared lamps to cure completely.