Plywood tank 800 gallon, choice of glass not so simple

[Jon_DK]

I know the question about glass thickness has been asked a billion times, but after reading through those discussions, I still can't figure out what to choose. The more I delve into the topic, the more difficult my decision becomes.

The construction of my plywood tank has just finished the sealing process, and I'm ready to install the front glass. The dimensions are 240 x 130 x 105 cm (95" x 50" x 41" in length, width, and height) with a capacity of approximately 3000 liters or 800 gallons. I've researched different types of glass, and here are my conclusions and considerations for the most relevant options:

OPTION 1:
25mm or 1" Float glass single sheet low iron (for reduced greenish tint)

Pros:

• Used for standard glass aquariums for decades.
• Very good transparency.
• Low or zero distortion artifacts.
• No risk of delamination (edge of glass can be exposed to water with no risk).
• Easy to bond/seal with standard silicone or MS-polymer.

Cons:

• "Just" normal glass strength means increased thickness and weight. For my required size, it's around 140kg.
• Impossible to source in Denmark. The thickest glass I can find is only 19mm.

OPTION 2:
12mm or 3/4" tempered low iron glass

Pros:

• Higher strength (5 times compared to standard float) = reduced mass.
• Reduced price.
• Easily available in several online glass shops.
• Likely more scratch-resistant compared to float.
• No risk of delamination (edge of glass can be exposed to water with no risk).
• Easy to bond/seal with standard silicone or MS-polymer.

Cons:

• Internal tensions can build up during the hardening process, leading to rare instances of "exploding" glass.
• Visual distortion is not uncommon, particularly visible when looking through the glass from the side (commonly known as "roller-wave").
• The glass can warp slightly due to the tempering process, but this might be negligible.

OPTION 3:
2 x 12mm or 3/4" tempered low iron glass, laminated with PVB foil (Standard glass lamination foil)

Pros:

• Very high strength.
• Widely available in most glass shops.
• If one glass breaks, the other should be strong enough to contain the water.
• Easy to bond/seal with standard silicone or MS-polymer.
• Commonly used in public aquariums (in Denmark), often with more than 2 sheets of laminated tempered glass.

Cons:

• Heavy, similar weight to a solution with normal float glass.
• Risk of delamination. The lamination foil along the glass edge must be protected from water and not exposed to standard silicone.
• Higher risk of visual distortion compared to a single sheet of tempered glass.

Other options exist, but these are the ones I've considered. I won't be using acrylic.

Option 1 is my preferred choice, but I can't find such thick glass in Denmark.

Option 2 seems successful for many DIY enthusiasts. Though the risk of sudden glass malfunction is minimal, seeking professional advice is prudent. The risk persists even with careful installation (no stress to any glass edge, wide and even silicone gasket, stiff frame, etc.).

Option 3 appears to be the safest choice. I need to figure out how to seal the glass edge to prevent water from reaching the lamination foil. I've consulted professional aquarium constructors who favor this solution for public aquariums.

I'm a little concerned about the risk of visual distortion like the common roller-wave distortion. Will it be noticeable?
Have any of you who have done DIY projects with tempered or laminated glass experienced visual distortion?
Does anyone know how to ensure the tempering process is done correctly to minimize excessive tension buildup and reduce distortion?

Maybe I'm overthinking this, but I want to get it right.

Thanks in advance for your comments and advice.

Best regards, Jon

 

[Jon_DK]

Here are some pictures of my project

4 new items by Jon Hagedorn

photos.app.goo.gl

 

[M1A1]

That looks very well built. Well done!

You're not overthinking it but if you limit your thinking to what's feasible, available, and cheap enough then you have a lot fewer options, exactly as you found.

I'm not sure I have ever seen any of the visual distortion or warping you mention with glass that was made in the last 50 years. Sure, plenty of old farmhouse cellar windows that are clearly wavy and maybe even thicker on the bottom than the top but the modern manufacturing processes don't allow for that sort of imperfection. Have you seen this first-hand on sample pieces or actual installations?

Yes, tempered glass will explode if damaged in exactly the wrong way. Annealed glass will also crack with that same damage so either way you're soaking wet and pissed off. This is always a con with any type of glass that doesn't have a lamination... which won't hold any water pressure if the glass fails anyways... Here in the USA, the tempering process is done at the factory so the local distributors or installers can't screw anything up on that aspect and likewise us consumers don't get to know or specify anything at all. Exactly how I'd prefer it to work but that's just me.

I don't have the calcs for laminated glass - too much proprietary data and modelling - so all I know is it greatly increases the cost!

TL; DR
Option 2 with tempered 3/4" low iron is sufficient by my calculations which show 0.65" minimum recommended, so technically 5/8" would be okay but I don't think I've ever seen that size anywhere. Calcs use glass design strength values from Germany, UK, & USA which put tempered permissible stress at 29-35 N/mm2 or 4466-5075 PSI for long term, water load type.

 

[Berts46ers]

Hi guys,
Just thought I would point out that 12mm is only 1/2” not 3/4” as you stated.
19mm thick is 3/4”.
Big difference between the 2 so just wanted to make sure you were aware.
Nice build and good luck.

Cheers

 

[fishdance]

Your tank is only 1 meter of water but option 3 is significantly better. Look for SGP film (laminate) ideally as it repells water unlike PVB which will swell.

To waterproof (and protect) the laminate film and glass edge, you can silicone glass or plastic trim strips - any thickness is fine, it's only for waterproofing. I used a 90 degree PVC plastic trim that went right around the exposed glass edge and Dow 795 neutral cure.

When you start siliconing in the glass panel, make sure you have some spacers. You want a gap underneath and all around the glass so your silicone bed is thicker and the glass doeent touch hard surfaces. You can pull the spacers out after cure or leave them in forever. I would start silicone at the top of the panel so if your slow applying silicone (or PU) or encounter problems, the cold joint seam where you complete the circuit is at the top where water pressure is lowest.

Have you looked at pond suppliers for glass?

 

[fishdance]

I've used 19mm + 1.5mm SGP + 19mm tempered glass ~ 40mm thickness and double laminate (3 glass sheets) ~ 62mm thickness without any distortion. Nowadays glass factories are predominantly automated and consistent quality.

 

[Midwater]

You seem to have answered most of your own questions.

As for 'visual distortion' from tempered glass, my large tank is 12' X 3' X 3' with 3/4" tempered glass. I can see no visual distortion.

 

[Jon_DK]

That looks very well built. Well done!

You're not overthinking it but if you limit your thinking to what's feasible, available, and cheap enough then you have a lot fewer options, exactly as you found.

I'm not sure I have ever seen any of the visual distortion or warping you mention with glass that was made in the last 50 years. Sure, plenty of old farmhouse cellar windows that are clearly wavy and maybe even thicker on the bottom than the top but the modern manufacturing processes don't allow for that sort of imperfection. Have you seen this first-hand on sample pieces or actual installations?

Yes, tempered glass will explode if damaged in exactly the wrong way. Annealed glass will also crack with that same damage so either way you're soaking wet and pissed off. This is always a con with any type of glass that doesn't have a lamination... which won't hold any water pressure if the glass fails anyways... Here in the USA, the tempering process is done at the factory so the local distributors or installers can't screw anything up on that aspect and likewise us consumers don't get to know or specify anything at all. Exactly how I'd prefer it to work but that's just me.

I don't have the calcs for laminated glass - too much proprietary data and modelling - so all I know is it greatly increases the cost!

TL; DR
Option 2 with tempered 3/4" low iron is sufficient by my calculations which show 0.65" minimum recommended, so technically 5/8" would be okay but I don't think I've ever seen that size anywhere. Calcs use glass design strength values from Germany, UK, & USA which put tempered permissible stress at 29-35 N/mm2 or 4466-5075 PSI for long term, water load type.

Thank you so much for your kind words and the very informative response.

I personally haven't witnessed examples of such distortion, but I've come across articles discussing it as a common issue. One instance where it might be significant is with large building facades featuring extensive glass areas. When sunlight reflects off these surfaces, it's possible that the "roller-waves" could become visible. This scenario contrasts sharply with the needs of the aquarium hobby.

Today, I spoke with an individual at a glass shop who claimed to have supplied glass to several public aquariums. He strongly advocated for laminated annealed glass over tempered glass. For my project, he recommended using 3 sheets of 10mm glass. When I inquired about his warning against tempered glass, he cited excessive deflection as the primary concern. However, upon conducting a Google search, I found a reputable article stating that deflection is the same for both annealed and tempered glass.

I believe gathering opinions from experienced individuals like yourself is a more reliable method for making a final decision, rather than solely relying on the advice of a single "self-proclaimed" glass expert. Thank you for providing the strength numbers and your invaluable advice.

 

[Jon_DK]

Hi guys,
Just thought I would point out that 12mm is only 1/2” not 3/4” as you stated.
19mm thick is 3/4”.
Big difference between the 2 so just wanted to make sure you were aware.
Nice build and good luck.

Cheers

Whoah, yes you're totally right. Thanks for pointing out. All I do is in "mm", so the (faulty) conversions to US inches was just for this post

 

[Jon_DK]

Your tank is only 1 meter of water but option 3 is significantly better. Look for SGP film (laminate) ideally as it repells water unlike PVB which will swell.

To waterproof (and protect) the laminate film and glass edge, you can silicone glass or plastic trim strips - any thickness is fine, it's only for waterproofing. I used a 90 degree PVC plastic trim that went right around the exposed glass edge and Dow 795 neutral cure.

When you start siliconing in the glass panel, make sure you have some spacers. You want a gap underneath and all around the glass so your silicone bed is thicker and the glass doeent touch hard surfaces. You can pull the spacers out after cure or leave them in forever. I would start silicone at the top of the panel so if your slow applying silicone (or PU) or encounter problems, the cold joint seam where you complete the circuit is at the top where water pressure is lowest.

Have you looked at pond suppliers for glass?

I did find one glass supplier who offered SGP film-type laminate, but PVB is much more common here. If I manage to effectively seal the edges, I assume PVB should be just as suitable as SGP?

My plan is to use spacers of 3 or 4mm thickness. I was thinking of placing the glass in the correct position leaning against the spacers, and then using a caulking gun with a thin or flat nozzle that can fit into this gap. The idea is to pump silicone or PU into the gap. Before attempting this on the actual project, I'll test it on a scrap piece of glass to determine its effectiveness. Hopefully, this method can help prevent bubbles inside the seams and ensure that the silicone bead doesn't start to dry on the surface before the glass is mounted, which could happen with the traditional method if I'm too slow. I do, however, have an electric caulking gun which should help speed up the process.

I've tried asking for glass at an aquarium (reef) shop with no luck. I'll give pond suppliers a try next.

Thanks again for your invaluable advice.