Resealing a used tank?

Fishingandreefing · Mar 9, 2020

Hi all, water tested a used tank with no leaks yet but some areas of the inside seems worn and peeling off about 10 to 15%. It might have caused by accidentally scrapped during cleanings.

I have read that few had success putting new silicone on top of old silicone.

Now I understand that this will not do any help on structure wise but looking for a peace of mind to prevent any future leaks.

any advice is greatly appreciated!

NeonRabbit221B · Mar 9, 2020

I resealed a 30 gallon about a year ago and it was a pain in the butt and turned out looking terrible... If you want to go through with it I woudn't suggest putting silicone on top of silicone as it never holds well. Make sure the area is very clean and wiped down with alcohol.

Pickwun · Mar 9, 2020

New silicone over old won't do much to prevent leaks. You'd just be doing it for looks, and unless you're the Rembrandt of silicone it's going to look like crap.

Mhart032 · Mar 9, 2020

Let me first start by saying i know this is not the proper method of resealing a tank, proper method would be removing all the panes of glass and redoing every joint and corner, but what i have done in the past is cut the corner beads out, clean the corners with alcohol, i taped the glass where i want the new joints to be, i wanted nice clean edges then used ASI adhesive to replace the older silicon/adhesive. I used the ASI from BRS, it worked on my current sump and a 34gal solana i resealed several years ago. Mind you these were not big 100+ gallon tanks with tons of water volume.

Mhart032 · Mar 9, 2020

Shoot left out a step, if your going to do this yourself.. Remove the tape before the adhesive drys!!! this is super important!

Cory · Mar 9, 2020

If you take apart the tank and reseal, once you scrape the old silicone off with a razor, use a soft wire wheel brush to get it perfectly clean. But for a 30 gallon id just buy a new one.

Super Fly · Mar 9, 2020

Pix may help to better evaluate. However from what I've read/heard, resealing tank silicone is not easy esp for first timers. If tank silicone condition doesn't give u peace of mind, then I'd move on... not worth it IMO.

Cory · Mar 9, 2020

Super Fly said:
Pix may help to better evaluate. However from what I've read/heard, resealing tank silicone is not easy esp for first timers. If tank silicone condition doesn't give u peace of mind, then I'd move on... not worth it IMO.

Yes the hardest part is getting something to cut apart the panels. I use fishing wire.

Neoalchemist · Mar 9, 2020

Just so you guys know. If you clean with alcahol the silicone wont bond properly. I got this straight from an adhesive manufacturer.
The silicone needs a certain ammount of moisture to bond.
So after cleaning surfaces you need to wipe them down with a clean rag moistened with clean water.

Cory · Mar 9, 2020

Neoalchemist said:
Just so you guys know. If you clean with alcahol the silicone wont bond properly. I got this straight from an adhesive manufacturer.
The silicone needs a certain ammount of moisture to bond.
So after cleaning surfaces you need to wipe them down with a clean rag moistened with clean water.

I never thought of that. I did have my concerns though of the residue left behind from the alcohol.

NeonRabbit221B · Mar 9, 2020

Glad that 30 gallon tank is no longer in the house...

Mhart032 · Mar 9, 2020

Cory said:
I never thought of that. I did have my concerns though of the residue left behind from the alcohol.

I never thought about the moisture aspect of it..

I use tech grade alcohol, i buy it by the gallon jugs. Its handy to have around the house for projects and cleaning electronics.

Neoalchemist · Mar 9, 2020

You fine precleaning with alcahol. Just make sure the glass isn't super dry, add some moisture. Silicone will cure just fine maybe even better under water. There shouldnt be any residue from 91% or better isopropyl any residue is from the water in the isopropyl 75% alcahol is 25% water but since isopropyl is hydrophobic it will chase all moisture away.
Weve been trouble shooting failed bonds between silicone adhesives and glass for a couple of months due to some unfortunate product failures.(laboratory glassware) and the adhesive manufacturers warn against pre-cleaning with any solvent.

NeonRabbit221B · Mar 9, 2020

Neoalchemist said:
You fine precleaning with alcahol. Just make sure the glass isn't super dry, add some moisture. Silicone will cure just fine maybe even better under water. There shouldnt be any residue from 91% or better isopropyl any residue is from the water in the isopropyl 75% alcahol is 25% water but since isopropyl is hydrophobic it will chase all moisture away.
Weve been trouble shooting failed bonds between silicone adhesives and glass for a couple of months due to some unfortunate product failures.(laboratory glassware) and the adhesive manufacturers warn against pre-cleaning with any solvent.

Any sources or links to your claim? I have never heard anything about adding moisture or sealing a tank under water.

mrlavalamp · Mar 9, 2020

Neoalchemist said:
You fine precleaning with alcahol. Just make sure the glass isn't super dry, add some moisture. Silicone will cure just fine maybe even better under water. There shouldnt be any residue from 91% or better isopropyl any residue is from the water in the isopropyl 75% alcahol is 25% water but since isopropyl is hydrophobic it will chase all moisture away.
Weve been trouble shooting failed bonds between silicone adhesives and glass for a couple of months due to some unfortunate product failures.(laboratory glassware) and the adhesive manufacturers warn against pre-cleaning with any solvent.

I am not sure what exact product they were referencing, but I am thinking you were given some bad information, at least as it relates to standard 100% silicone products (ASI, Mometive 108 https://www.momentive.com/en-us//pr...roductId=268dd400-2250-4bca-9fed-83a3cb3d4cc0 ).

Silicone will not cure better under water. It will not cure properly or really at all underwater.

The surface needs to be VERY clean with no residues on the glass alcohol or MEK wipe before sealing will do well to clean the old residues.

The silicone bonds to tiny cracks in the glass and you need to get all old silicone out of those cracks. They are microscopic so you cannot see them. Silicone will not bond to old silicone at all really, so if you dont clean the surface correctly the new silicone will be very easy to peel up.

EDIT:

Neoalchemist · Mar 9, 2020

Nobody reads. What i said was silicone will cure just fine MAYBE even better under water. But what I learned firsthand from a high end silicone adhesive manufacturer is that the silicone needs some miosture to form a proper bond to glass. And solvents overly dry surfaces. I can site the manufacturer when I get to work and you can give them a call and argue with them. All I know is that this helped solve major problems with silicone not bonding to glass properly.
And silicone will cure just fine in water, Ive done it. I probably shouldnt have used the word "better" when referring to curing under water because I dont know that for sure. What I do know is that advise from the adhesive manufacturer to moisten the surfaces has solved our silicone bonding issue. This is a pharmacutical manufacturing environment so theres a ton of money on the line. If these processes fail or get contaminated the loss could be in the millions so it has to be right.

Neoalchemist · Mar 9, 2020

mrlavalamp said:
I am not sure what exact product they were referencing, but I am thinking you were given some bad information, at least as it relates to standard 100% silicone products (ASI, Mometive 108 https://www.momentive.com/en-us//pr...roductId=268dd400-2250-4bca-9fed-83a3cb3d4cc0 ).

Silicone will not cure better under water. It will not cure properly or really at all underwater.

The surface needs to be VERY clean with no residues on the glass alcohol or MEK wipe before sealing will do well to clean the old residues.

The silicone bonds to tiny cracks in the glass and you need to get all old silicone out of those cracks. They are microscopic so you cannot see them. Silicone will not bond to old silicone at all really, so if you dont clean the surface correctly the new silicone will be very easy to peel up.

EDIT:

Solvents will not remove the silicone in the cracks and pores. Niether alcahol, acetone or methanol nor any petroleum based solvent will cut, thin or help remove silicone. Ive been dealing with this for about 25 years.

Neoalchemist · Mar 9, 2020

mrlavalamp said:
I am not sure what exact product they were referencing, but I am thinking you were given some bad information, at least as it relates to standard 100% silicone products (ASI, Mometive 108 https://www.momentive.com/en-us//pr...roductId=268dd400-2250-4bca-9fed-83a3cb3d4cc0 ).

Silicone will not cure better under water. It will not cure properly or really at all underwater.

The surface needs to be VERY clean with no residues on the glass alcohol or MEK wipe before sealing will do well to clean the old residues.

The silicone bonds to tiny cracks in the glass and you need to get all old silicone out of those cracks. They are microscopic so you cannot see them. Silicone will not bond to old silicone at all really, so if you dont clean the surface correctly the new silicone will be very easy to peel up.

EDIT:

In reading through your link it is repeated multiple times curing at 50%relative humidity which is quite a bit more humid than average. I have touble getting my house above 30% humidity. Theres you moisture requirement.

mrlavalamp · Mar 9, 2020

I have no skin in the game here really, but was doing some research on resealing tanks not too long ago.

I linked Momentive RTV 108 because it is highly recommended by professionals and you will find it mentioned all over Reef2reef and reefcentral as THE silicone for building and re-sealing tanks.

having a humid environment is different than being submerged.

It took 3 trys for me to get my 120gallon resealed well enough for me to be happy with it. 1st time looked like ****, 2nd time I didnt get the tape off in time and it skinned at the end, 3rd time I got a helper and taught them how to run the gun on some scrap glass so I could follow along and smooth it. For larger tanks a helper is critical, you just cannot move fast enough.

cvrle1 · Mar 9, 2020

@Fishingandreefing you never mentioned how big of a tank it is. If it is smaller tank, 55G or less, it may be just easier to buy a new one from Petco when they have their $1 a gallon sale (on right now)