I haven't used rubberised spray-on coatings much, but a real handy tip is to warm up the tin first by placing it in a bucket of warm water (with a weight on top of the can to keep it submerged) for about 10-20 minutes. This helps insure that when the particles come out of the can, they don't clump together. Also make sure you don't spray it too close or too heavily per coat, or it can start to bubble.