Silicone over old Silicone?

brodylane1122

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I have a 75 gallon tank that I filled up and tested for several hours. No leaks at all. I'm the type that likes to be safer than sorry. So, would it be beneficial to put more silicone over the old silicone? Just to be safe?
 

cichlidman

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i would scrape the spots in question and replace it for a good seal. It would not bond correctly with the old
 

skjl47

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Hello; My experience is that new silicone dose not adhear well to old silicone. Some have reported such success after a thorough abrading/scrubbing of the surface of the old silicone. This has only worked for me on occasion. The level of scrubbing necessary may compromise the present non leaking seal or you could get lucky.
I have filled old tanks with discolored silicone and had them hold fine for substantial amounts of time. Any opinion on a sight unseen tank is going to be a guess, but I would likely leave things alone. Without some indicating criteria other than being old silicone it would not seem worth the trouble.
Perhaps the tank can be filled in a safe place and left to sit for a week or two to see how it holds, or a few hours, days depending on your patience.
Good luck
 

psalm18.2

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Re-sealing a tank isn't that hard. I was surprised how easy it is. Scrape all old silicon with a razor blade. Wipe down with vinegar, scrape again. Let it dry. Apply new silicon, spread with you finger, and let dry 7 days.

Not hard at all.
 

beginner

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is it not the inner seal that's important??? recaulking the inside wont save world if the seal between the panes give out
 

cichlidman

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Re-sealing a tank isn't that hard. I was surprised how easy it is. Scrape all old silicon with a razor blade. Wipe down with vinegar, scrape again. Let it dry. Apply new silicon, spread with you finger, and let dry 7 days.

Not hard at all.
7 days??? lol lucky if i wait 2
 

soltarianknight

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is it not the inner seal that's important??? recaulking the inside wont save world if the seal between the panes give out
When you put down the new outer layer you push new silicone into any cracks on the inner seal and also create a barrier linking the two pieces that water cannot get through to actually reach the point where they connect.

IME if it flakes or you can pick at it with your fingers then it is time to reseal. Just did my first total reseal on a 37hex a few weeks ago, took all of maybe an hour tops to do the entire thing and that was with 12 seals to do as opposed to a standard rectangles 8. It is very easy imo. Use some acetone nail polish remover after the initial scrape to get any remaining residue.

Or, if it doesn't look bad and is just discolored then leave it be. I have had PLENTY of discolored seals on tanks, a lot of times it can indicate simply that certain medications were in the tank at some point(my 10gal seals are stained blue/green). Definitely check it though
 

soltarianknight

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I waited 24 hours, i am in fact, shamed. It worked though, just air the thing out real well. Keep it outside where it can get a breeze to help cure faster.
 

beginner

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if you look closely at the seal from the end, you want to be able to see straight through to the other side. a little haze is ok but air bubbles are not exceptable. we are talking about a tank that'll be set up for years. I don't hesitate to tear a tank right apart. a few years ago I had a 90 gallon blow a seal that I had just caulked over. don't be afraid to take the bottom trim off and inspect the bottom seal too
 
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