Resealing tank

[Aquattro]

I'm resealing the 180 and planned on doing just the corners (switching from clear to black silicone) and then recalled I might have read silicone doesn't stick to silicone somewhere.
Do I need to do the whole tank, or can I just do the corners? The existing seal is fine, just doing corners for aesthetics...thx

[plutoniumJoe]

Once the silicone dries new stuff wont stick well. If you cut out the corners and the Glass on glass seem is still good you can just redo the corners. It wont be as strong as a total new seal but you will still have the seal from the glass to glass as well as the corner seal just not a significant seal between the two.

-- Your millage may vary.

[Aquattro]

Oh, no, just doing corners, but was trying to get away with vertical corners, not the bottom edge. I decided to do it all, too hard to change my mind when it has water in it

[hillegom]

You will have better piece of mind if you do the bottom as well as the verticals at the same time. You are right, silicone does not stick to cured silicone very well.

[plutoniumJoe]

Yes you definitely should do the bottom as well to create a continuous new seal. If you just do the vertical seams you wont have good bonding at four points where the verticals join the horizontal and these points are where there is considerable pressure.

[sphelps]

Silicone will stick to cured silicone provided it's clean. This is strange myth which makes little sense. When building larger tanks with thicker glass it's actually best to do the seams in two steps to ensure it silicone cures throughout the seam.

The confusion must relate to the old silicone being contaminated or covered in algae and of course the silicone itself can be difficult to clean. So on the safe side it might be best not to rely on such a bond but realistically if you clean it, it'll be fine. You can use alcohol to clean the old silicone in the area where the new will overlap.

If you don't agree or just unsure, try an experiment. Simply make a "goop" of silicone and let it cure, next apply some more to make another "goop" that attaches to it. Let that cure and see how strong the bond is.

If it's really true that silicone won't stick to silicone (even sounds ridiculous) then you should never reseal a tank in the first place. This is because you can't remove all the silicone in a reliable way from the glass unless you use an actual chemical to remove it which you don't want to use unless you completely dismantle the tank.