Can not say for sure what the life limit of it is because I had to take it down after only a few months, but I used fermica to waterproof the inside of my 600g plywood tank and it worked great for the time I had it. I used silicone to seal the corners and the viewing window. I never found any definitive information on the long term permeability of fermica continuously exposed to water but when I took it down I broke the fermica to see if it had any water under it and there was none.