Silicone and bracing failure
- Thread starter 805hd
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jjohnwm
Not up for a back and forth BS pissing contest?! Damn. 
āyou can get away with 3/8 glass, trust me I work at foot lockerā.All good man, Iām not interested in that either. I came here for educated opinions. Between
Backfromthedead
and yourself I feel like I more than got my answers. What I do with that is still to be determined 
haha!Unfortunately the glass is tempered which sucks cause if I choose to scrap the tank itās essentially useless.
You are definitely not the first person to point fingers at the silicone. I ordered it on amazon purely based off of price and well, it looked cool. Release the kraken! Didnāt know the kraken would release the glass!
I used acetone to clean all mating surfaces of glass prior to silicone. One thing not to mentioned was the silicone holding the center braces did go from jet black to almost a dull black almost grayish color with water in the tank. Looking back on it, that was definitely a sign of how much tension the silicone was under.
Just out of curiosity, when using silicone to join glass. Especially glass that will be under pressure is there a rule of thumb as to how much silicone should be between the two surfaces? Would it vary with glass thickness, tensile or shear forces?
Obviously you donāt want a razor thin layer of silicone but you also probably wouldnāt want it to be 3/4 thick either.
Ah the old silicone seam thickness question. Another one where I can really only comment "what I do".
For smaller tanks, under 100g of height thats not unusually tall, i clamp the structural panels together until they are just barely...almost..touching, than hold them together with masking tape for the duration of cure time. So yeah nearly "razor thin". This gives the strongest adhesion in my mind, hardly any wiggle room but just enough silicone to avoid any glass-to-glass contact if the tank is bumped or the water shifts suddenly for some reason.
Well with larger tanks, those same issues become real dangers, since as we've learned already the forces involved multiply quickly with length and especially height, especially when considering shock loading. You want no possibility at all of glass on glass contact with larger tanks.
Here's my smallest tank atm, but every bit my pride and joy, a 200g 7x2x2 oceanic that was built sometime in the 90s:
Hey wait, zoom in man! What the hell is that?
It's a 1/16" silicone spacer! I learned after building some of my first larger tanks that there should be a small, but not exactly spacious gap in the structural seams. These old oceanic tanks are far superior than anything in the big box stores these days as well as any of my tanks hibernating in the backyard lol, which is why I keep this one up and running.
This is also where a quality structural adhesive silicone becomes a part of the equation. Some silicones are obviously stronger than others, but some are better at others at retaining that strength under stress. This is one reason I really like DC 795, which keeps most of its strength even when stretched by up to 50%.
Now for something like a eurobrace, the horizontal pieces on top can be clamped/pressed down pretty tight. You'll have to cut the lateral under-hanging braces with a small gap to maneuver into place, but the lateral braces will have so much silicone adhesion where they contact both the side panel and horizontal brace that they'll be the last things to expand/budge/move on the tank, more likely to shatter somewhere in the middle under stress than rip off at the seam if installed correctly.
Anyways, I'm going on and on. That's the gist of what I think I know lol.
For smaller tanks, under 100g of height thats not unusually tall, i clamp the structural panels together until they are just barely...almost..touching, than hold them together with masking tape for the duration of cure time. So yeah nearly "razor thin". This gives the strongest adhesion in my mind, hardly any wiggle room but just enough silicone to avoid any glass-to-glass contact if the tank is bumped or the water shifts suddenly for some reason.
Well with larger tanks, those same issues become real dangers, since as we've learned already the forces involved multiply quickly with length and especially height, especially when considering shock loading. You want no possibility at all of glass on glass contact with larger tanks.
Here's my smallest tank atm, but every bit my pride and joy, a 200g 7x2x2 oceanic that was built sometime in the 90s:
Hey wait, zoom in man! What the hell is that?
It's a 1/16" silicone spacer! I learned after building some of my first larger tanks that there should be a small, but not exactly spacious gap in the structural seams. These old oceanic tanks are far superior than anything in the big box stores these days as well as any of my tanks hibernating in the backyard lol, which is why I keep this one up and running.
This is also where a quality structural adhesive silicone becomes a part of the equation. Some silicones are obviously stronger than others, but some are better at others at retaining that strength under stress. This is one reason I really like DC 795, which keeps most of its strength even when stretched by up to 50%.
Now for something like a eurobrace, the horizontal pieces on top can be clamped/pressed down pretty tight. You'll have to cut the lateral under-hanging braces with a small gap to maneuver into place, but the lateral braces will have so much silicone adhesion where they contact both the side panel and horizontal brace that they'll be the last things to expand/budge/move on the tank, more likely to shatter somewhere in the middle under stress than rip off at the seam if installed correctly.
Anyways, I'm going on and on. That's the gist of what I think I know lol.
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What the...?!?!?
Is that a dime I see permanently embedded into that tank as a spacer?!?!?
Ten cents times two per joint times 8 joints? A buck sixty for spacers??? Are you mad?!?!?
I obviously don't belong in this rich kids crowd. My spacers are fine finishing nails, almost like pins, two or three per joint laid crosswise across the bead, not quite projecting into the interior of the tank. Position the glass, run your finger down the inside of the whole seam to smooth and concave it, then move on to the next seam. Leave the spacers in place until the silicone is fully cured and then grab the exposed heads on the outside and twist/pull them out, to be saved for the next tank.
The tank builder I worked for did this for every tank using 3/8 inch or thicker glass that he built; many hundreds that I know of. Add a few dozen more assembled in my hamfisted style under his tutelage, plus a couple dozen more built for myself. It works like a charm.
A buck sixty for spacers...the very idea...
Is that a dime I see permanently embedded into that tank as a spacer?!?!?
Ten cents times two per joint times 8 joints? A buck sixty for spacers??? Are you mad?!?!?
I obviously don't belong in this rich kids crowd. My spacers are fine finishing nails, almost like pins, two or three per joint laid crosswise across the bead, not quite projecting into the interior of the tank. Position the glass, run your finger down the inside of the whole seam to smooth and concave it, then move on to the next seam. Leave the spacers in place until the silicone is fully cured and then grab the exposed heads on the outside and twist/pull them out, to be saved for the next tank.
The tank builder I worked for did this for every tank using 3/8 inch or thicker glass that he built; many hundreds that I know of. Add a few dozen more assembled in my hamfisted style under his tutelage, plus a couple dozen more built for myself. It works like a charm.
A buck sixty for spacers...the very idea...
Backfromthedead
Per usual this makes total sense... is that actually a dime? ha!Thats essentially what I did with the bracing, clamped down what I could and taped everything to hold through the initial curing time.
I'm learning a lot here besides the standard "taller tanks need thicker glass" bit
does the pressure/height ratio apply to acrylic as well?
And doesn't the quality of glass fabrication affect overall strength? Not the seams of course but pressure load.
My 6 footer is an unusual combo: 1/2" tempered on the front and sides, 1/2" annealed on the back and 3/4" annealed at the bottom. the top brace is marine grade aluminum and so thick it's hard to put hob filters on. Maybe that's why the 1/2" works on my 225? Dunno...Custom Aquariums says they go with a factor of 3.8.
Now as some of y'all know, I have a future boxy tank project in the works. So going from memory the dimensions are 30 or 33" tall, 23" wide and 40" long. So what would be an ideal thickness of both glass and acrylic. The tank is being ordered but I'm not looking at needing a crane to move it either.
would 33" v s 30" in height make a big difference in thickness?
does the pressure/height ratio apply to acrylic as well?
And doesn't the quality of glass fabrication affect overall strength? Not the seams of course but pressure load.
My 6 footer is an unusual combo: 1/2" tempered on the front and sides, 1/2" annealed on the back and 3/4" annealed at the bottom. the top brace is marine grade aluminum and so thick it's hard to put hob filters on. Maybe that's why the 1/2" works on my 225? Dunno...Custom Aquariums says they go with a factor of 3.8.
Now as some of y'all know, I have a future boxy tank project in the works. So going from memory the dimensions are 30 or 33" tall, 23" wide and 40" long. So what would be an ideal thickness of both glass and acrylic. The tank is being ordered but I'm not looking at needing a crane to move it either.
would 33" v s 30" in height make a big difference in thickness?
All to do with pressure. Deeper you go under water the higher the pressure. If I have my maths (and memory) right every meter is 9.8 times the pressure.
As for silicone I would have siliconed front to back brace on the inside of the front and back panels on top of a left to right piece. So basically the four pieces of glass you have at each side of the tank I would have all siliconed together as a square on top of each other at the corners, which is then siliconed to the front and back panels below the top of the tank inside it. Can then put that silicone both on top and below each piece of glass, doubling the silicone contact to glass. Ok you may loose an inch of tank height.
Alternative of course if you can weld is a welded angle iron rim that fits on the top of the tank glass to stop it bowing and act as a bracing, similar to the plastic ones used to make tanks look better. Only issue is if you already have a lid to fit.
As for silicone I would have siliconed front to back brace on the inside of the front and back panels on top of a left to right piece. So basically the four pieces of glass you have at each side of the tank I would have all siliconed together as a square on top of each other at the corners, which is then siliconed to the front and back panels below the top of the tank inside it. Can then put that silicone both on top and below each piece of glass, doubling the silicone contact to glass. Ok you may loose an inch of tank height.
Alternative of course if you can weld is a welded angle iron rim that fits on the top of the tank glass to stop it bowing and act as a bracing, similar to the plastic ones used to make tanks look better. Only issue is if you already have a lid to fit.
No...no..NO!
Not pressure. Force. The hydrostatic force acting on the side wall of a tank is what determines the thickness of glass needed on all panels of the tank. Water pressure simply describes the weight of water, air, everything above at a given point (bottom of tank for our purposes usually). It is absorbed completely by the bottom glass and for this reason there a force that pushes on the side panels.
Hydrostatic force is calculated in a water tank with a integral equation. For some reason the link is no longer working that explains all this better than i can, but In a tank with water, this is simplified to:
F=1/2(0.036xLxH^2)
F being hydrostatic force
L being the length of the tank
H being the height of the water column
Getting tired of reading "height is all that matters" NO. the length of the tank absolutely matters. This is why a tank like
FINWIN
is suggesting at 40" long and 33" high may not require the same thickness panels as a tank 80" Long and 33" high.
I'm not doing all the calculations cause 1. I don't know how and 2. I'm an expert half-asser.
We calculated force on the front panel of 72x24 at 746 lbs. earlier in this thread. Every reputable manufacturer in the world makes 6x2x2 tanks out of 1/2" glass. So in my mind 1/2" would work just fine for a tank with a front panel 40x33 and a force of 737 lbs.
The bottom is a different story since the height is different. But I don't know all those deflection calculations so if I'm building that tank it's getting a 3/4" bottom and that's that.
FINWIN
i must confess when I delivered that stand to your home I had an ulterior motive...I wanted to inspect that big tank 
. I think you hit it on the head. That beefy aluminum frame both reinforces the entire bottom silicone seam and augments the front panel by encasing the top and bottom of the glass in 2-3" of thick aluminum. In my mind this effectively shortens the water column that is only supported by the glass and adds the strength of that aluminum to the entire height which is a ridiculous bunch more math so lets just say customaquariums has it figured out better than we do, obviously a very strong design when inspecting the tank...I still wanted to get my long straightedge out of the truck and check for deflection though 
Not pressure. Force. The hydrostatic force acting on the side wall of a tank is what determines the thickness of glass needed on all panels of the tank. Water pressure simply describes the weight of water, air, everything above at a given point (bottom of tank for our purposes usually). It is absorbed completely by the bottom glass and for this reason there a force that pushes on the side panels.
Hydrostatic force is calculated in a water tank with a integral equation. For some reason the link is no longer working that explains all this better than i can, but In a tank with water, this is simplified to:
F=1/2(0.036xLxH^2)
F being hydrostatic force
L being the length of the tank
H being the height of the water column
Getting tired of reading "height is all that matters" NO. the length of the tank absolutely matters. This is why a tank like
FINWIN
is suggesting at 40" long and 33" high may not require the same thickness panels as a tank 80" Long and 33" high.I'm not doing all the calculations cause 1. I don't know how and 2. I'm an expert half-asser.
We calculated force on the front panel of 72x24 at 746 lbs. earlier in this thread. Every reputable manufacturer in the world makes 6x2x2 tanks out of 1/2" glass. So in my mind 1/2" would work just fine for a tank with a front panel 40x33 and a force of 737 lbs.
The bottom is a different story since the height is different. But I don't know all those deflection calculations so if I'm building that tank it's getting a 3/4" bottom and that's that.
FINWIN
i must confess when I delivered that stand to your home I had an ulterior motive...I wanted to inspect that big tank . I think you hit it on the head. That beefy aluminum frame both reinforces the entire bottom silicone seam and augments the front panel by encasing the top and bottom of the glass in 2-3" of thick aluminum. In my mind this effectively shortens the water column that is only supported by the glass and adds the strength of that aluminum to the entire height which is a ridiculous bunch more math so lets just say customaquariums has it figured out better than we do, obviously a very strong design when inspecting the tank...I still wanted to get my long straightedge out of the truck and check for deflection though
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