Hi Mark,
sorry to be a little slow in answering,but currently involved in shifting house. Re silvering: decided on the spray method as it seemed the mechanics of application were more suited to large surface mirrors. I didnt use any spin or other in applying the silver. Simply stood the mirror(s) on edge and sprayed on the chemicals as per instructions. Coatings must be reasonably uniform in thickness as in scope images of similar quality to pre coating images, but much much brighter. Objects like Omega Centauri and the like
amazing. I thought my 14" dob was great, but now such objects seen go to a new level.
Regarding coating longivity: Its about 6 weeks since the coatings were applied and at this stage I see absolutely no deterioration of the reflective surfaces so am hoping 6 months to a year of use before recoating,(time will tell). The coating procedure is so simple and inexpensive that I have no reservations about recoating when it becomes essential.