[scolley]

Originally Posted by Green_is_beautiful

Whenever people talk about reapplying silicone in old tanks that developed a leak - they mention that you cant just cut out one seam (the leaky one) and reapply silicone there - you have to redo the whole tank. It's because (supposably) old silicone doesnt stick well to new - and you just end up having a leak where the old meets the new.
Now you obviuously did the opposite - working on a seperate panel every 2 days (or more if humidity was lower). Basically having new+cured silicone meeting in a lot of areas.
Going from your experience with silicone - is it really necessary to redo the whole tank if you have a leak somewhere ?

Well, I've gotten it from the experts that silicon sticks to silicon very, very well. But maybe they meant fresh silicon, not aged silicon. I also got it from the experts that no silicon manufacturer makes silicon that they will say works for aquariums. Other companies buy the manufacturers' silicone, who then repackage it, and call it "aquarium" silicon. But the manufacturers know that silicon breaks down underwater, and does so much faster than silicon that is just exposed to air.

So they take the conservative position and will not warrant that it will work underwater - its life it too limited in that application. So maybe that is why, when a tank springs a leak that you redo the whole thing - you take that as an indicator that it is all breaking down, with this as just the first warning sign. Sounds good to me.

As to the fresh stuff sticking... well I sprung a LOT of leaks before everything was OK, but I never sprung one at at point where I joined cured (or semi-cured) silicon to fresh. So I trust the advice of the experts on that - silicon sticks to silicon. Or at least it does if it is not old silicon.

Originally Posted by Solace

just cant see the ability of the silicon seals holding up to the stress of the water pressure, i dont get the math on it.

I don't do much math at all myself. But I can tell you silicon is amazingly strong. But its strength is is primarily tensile. It is weak with adhesion, which is exactly what you need most for an aquarium - you need it to not rip away from the glass. That's why the commercial stuff fails if your seams are not large. The professional grade stuff is substantially stronger in adhesion strength. Most people's experience with silicon, and I suspect the experience you are drawing your reasonable observations from, is commercial silicon.

The stuff I'm recommending is something entirely different - much, much stronger.