Thank you for your post and please know that coating should not only last 15 to 30 minutes. Itís obvious that thereís an issue with the heads you received. If that time frame is accurate and you encountered this under normal usage please contact your dealer or also feel free to contact us directly. We stand behind our product 100% and we expect only the highest level of quality from every drumhead we manufacture.
Thank you for your support and I apologize for the inconvenience.