650 Glass Build and leak

[FisheadFrank]

Hey everybody! I purchased a used 102x38x38x "3/4" (closer to 1/2") tempered glass aquarium. Tank/stand are completely level. Tank was built on Jan 31st of 2023. Tank sat until I could get the stainless steel brace for the top welded and installed (May 11th of 2023). It had plenty of cure time. Tank was slowly filled from May and I added water every week until it was full in June sometime. Drained the tank and installed the background and decor. This also took some time to get and do. Tank was full and ready by the 20th of August and had its first fish in there on August 27th. October 7th 2023 is the day it leaked. I've used DAP silicone in the past to reseal a 30" tall 150 gallon. I'm hoping it was due to this silicone and nothing to do with the build. There is a picture of the silicone when we got in the tank after it was all dried and you can see the silicone was cracked.

We resealed the tank on the 16th of December using ASI silicone. Wondering if anyone had any advice or feedback. I plan on waiting until January 13th to refill which gives us 28 days of cure time. It was a thick bead of silicone..

 

[celebrist]

That sucks, I hope you get sorted out soon

 

[M1A1]

So did you use the DAP silicone to reseal the tank right after you bought it?

 

[FisheadFrank]

That sucks, I hope you get sorted out soon

Thank you

So did you use the DAP silicone to reseal the tank right after you bought it?

No, the tank sat for 5+ years in my garage. I cleaned it, very thoroughly before using DAP.

 

[fishdance]

For a tank of this size (depth) you require structural grade silicone. Generally this is mentioned in the products technical specification sheet and equates to >30 MPa tensile shear so it's not surprising the DAP failed. I had a quick look at ASI Aquarium Silicone which has about 3 MPa tensile. However since you have already used it, you might as well do a water test once it's cured.

The highest stress zone is midway of the longest panels at the bottom so an internal glass brace along the long panel at bottom greatly increases the adhesion area - similar to having a bottom panel twice as thick. Most big tanks run the bottom brace along all four sides for uniformity. Some very big tanks (8m +) use a split base to enable movement.

If you do have to tear down and reseal, use structural grade PU instead of structural grade silicone because you can simply patch any future leaks with additional PU as new PU will bond to cured PU making repairs or modifications very simple. The structural aspect of PU significantly superior as well.

However structural glazing silicone will suffice.

Tempered glass is far stronger than float glass but is more flexible. Good choice of glass but requires more brace.

 

[FisheadFrank]

For a tank of this size (depth) you require structural grade silicone. Generally this is mentioned in the products technical specification sheet and equates to >30 MPa tensile shear so it's not surprising the DAP failed. I had a quick look at ASI Aquarium Silicone which has about 3 MPa tensile. However since you have already used it, you might as well do a water test once it's cured.

The highest stress zone is midway of the longest panels at the bottom so an internal glass brace along the long panel at bottom greatly increases the adhesion area - similar to having a bottom panel twice as thick. Most big tanks run the bottom brace along all four sides for uniformity. Some very big tanks (8m +) use a split base to enable movement.

If you do have to tear down and reseal, use structural grade PU instead of structural grade silicone because you can simply patch any future leaks with additional PU as new PU will bond to cured PU making repairs or modifications very simple. The structural aspect of PU significantly superior as well.

However structural glazing silicone will suffice.

Tempered glass is far stronger than float glass but is more flexible. Good choice of glass but requires more brace.

Very informative and helpful. Thank you!

What is PU?

 

[Backfromthedead]

F fishdance
Polyurethane? Really? How well does that stick to glass? Are we talkin just the seals or the structural seams as well?

 

[jjohnwm]

F fishdance
Polyurethane? Really? How well does that stick to glass? Are we talkin just the seals or the structural seams as well?

Just saw that post, and my eyebrows shot right up just like yours did, Backfromthedead .

If there's a PU adhesive that can be used to build all-glass tanks...and which will bond to itself after the initial layer is cured...that will be a game changer, for me at least.

F fishdance ? More info, please?

 

[FisheadFrank]

I did a quick calculation. I could be way off so please correct me if I’m wrong. Tank is 650 gallons probably holds a little less but there will be some rocks and sand in it. I like round numbers so let’s call it 5600 lbs. Tank is 102” by 38” so the silicone on the bottom is 240”. Since the thickness is could be less than an inch let’s say 200”.

5600 / 200 = 28 PSI

The ASI Silicone is rated at 200 PSI. So it should hold no problem. I hope I’m not missing anything.

It’s been 3 days now. Fingers crossed. Going to give it at least a month before putting fish in.

 

[M1A1]

I've never found an actual calculation for the sealant/adhesive strength but if the calc for panel thickness is any indication, it won't be that simple. Length of the largest panel, height of the water, ratio of height to length, max allowable stress on the panel which depends on the type of glass, and a proprietary variable based on the height/length ratio are all used to calculate the minimum panel thickness.

A 10mm annealed (not tempered) glass panel has a max allowable stress of about 1000 PSI so the ASI silicone tensile strength of 3 MPa or about 435 PSI would seem to be a little low, the joints would be the weak point. Switching to this magical PU (any recommendations, F fishdance ? ) with 30 MPa strength would definitely strengthen the joints.

But just so we're clear, the numbers above in hundred or thousands of PSI are the extreme limits. At 38 inches tall, this tank only has 1.3 PSI of pressure at the bottom of the glass. So if everything works at even a tenth of the rated strength then the safety factor is still really high.

Great looking tank and I'll take the nerd glasses off now.