Before you start this thread, about building a 75g glass tank, please be warned... This tank held for more than a year, but one side failed - catastrophically - one afternoon. IMO that should not discourage you from trying this. I discuss why it failed in this thread. Give it a read.
I understand why, and it is quite preventable. But I can't prove it.
- SCOLLEY June 9, 2007
I recently built a 75g (approx.) aquarium out of glass and silicone. No frame, no bracing. It was successful, but it was difficult. As I built it I tried to document the entire experience so that I could pass along the lessons I learned in that process.
I had intended to create a “How-To” document. But I’ve become uncomfortable with the concept of step-by-step instructions for a tank of that size. There are too many variables; too many things can go awry in the construction and assembly process, making step-by-step instructions useless. If you intend to build something like this yourself, your knowledge needs to be sufficient for you to create your own step-by-step instructions. Based on the information I’m providing here, and using the other sources I’ll reference, you should be able to do that. And more important, when something you don’t expect happens – like running out of silicone just as you are putting on the last pane of glass, for example – you’ll have enough knowledge to know what that means to your plans, and how to get your construction process back on course.
My own experience left me convinced that some of the techniques I used could be improved. But if you want to build such a thing yourself, the things I learned should help enable your success.
I have a very long thread here
that documents my entire tank building experience. It provides a lot more details than you will find here, just less well organized. There’s even a bit of humor in it – it was needed. You will find that I had a lot of missteps in my tank building process… steps that caused a painful amount of rework (removing and replacing glass) before I finally got it right.
In that process I learned a lot – from doing it wrong, figuring out why, then doing it right and learning from the change. If I had known then the things I know now, my whole tank building project would have been easier, faster, and cheaper.
All of the information here is specific to building a 75 gallon tank like mine. It worked for me. I believe (but cannot guarantee) that it will work for you too, if you do exactly as I specify here. But if you deviate from what I’m describing here, I suggest you read my thread, talk to people, and do your research first. Good luck!
Why build a tank?
I didn’t want to build a tank – I’m too busy, and didn’t know how. But I did have a few criteria in a tank that I refused to compromise on, so I was left with little choice:
1) A frame-less, rimless, all glass, tank (ADA like)
2) Having cosmetically lovely glass edges and small, very neat, silicone seams. This implies not buying from vendors that do not have a proven and consistent record of providing such tanks.
3) Not spending more than $1000 on a tank, including shipping. Hoping to hit half that.
4) A low iron (clear glass, not green) tank.
5) A non-tempered bottom, to allow bulkhead holes to be drilled.
6) Very small, neat silicone edges (difficult to see).
All glass tanks of varying quality can be purchased. But within the US the geographic availability varies greatly unless you are willing to bear very large shipping costs.
What will it cost? What do I need?
The glass is the primary expense. If you include bulkhead holes, as I did, that will add cost. I you elect to use normal green “float glass” used in most tanks, you should be able to get the glass from a local glass cutter for less than $200. If you are asking for some variety of ‘low iron”, or clear glass, expect at least double that cost. Probably triple. DO NOT buy tempered glass of any variety.
Tools and consumables constitute the rest of the cost. I don’t remember all of my exact costs, but it was something like this:
60” J Clamps – (6) at $15 each
Cabinet right-angle braces – (2) at $12 each
Acetone – (1) 12 oz. can at $4
Razor blades – (6) boxes of 10 Exacto brand blades at $3
Razor knife – (1) Exacto brand $4
Sand paper – (1) pack #120 grit, $3
Square, or Right-angle, ruler – (1) ruler at $7
Silicone – (4) tubes RTV108 at $9 each, (translucent or black), FYI – you should buy (1) extra
Caulking gun – (1) at $5
Masking tape – (3) large 2” wide rolls, 3M brand at $5 each, FYI – cheap stuff sticks to the glass
This totals well over $200 without the glass, more if you have to include shipping and or tax. And that does not include the cost of glass.
All silicones are not created equal. AGA Aquarium silicone is similar to GE Silicone I "window and door", and is made by DOW. It also appears to be the same thing as Perfecto Aquarium silicone. These silicones are only appropriate for aquariums with large seams, something I have little experience with – I started my aquarium with AGA Aquarium silicone and kept popping seams. But then I switched to GE RTV108, which is apparently used by some commercial tank builders. With GE RTV108 you can make very small seams. I gather SCS1200 works very well too, but it is difficult to get your hands on in small volumes. Both of these have a much higher adhesion strength than commercial grade silicone like GE Silicone I or “aquarium” silicones, your typical stuff available to use at Big Al's or Home Depot. These commercial (not professional) silicone have so little adhesion strength the manufacturers don’t even list it in their performance specs.
Bottom line - commercial grade silicones can
work with big seams, but professional grade silicones do
work, and with small seams.
There is no need for external seams – all seams are on the inside of the tank. All excess silicone on the outside should be wiped away as a part of the assembly process. Using GE RTV108 silicone, ¼” is sufficiently wide for your interior vertical seams. But on the bottom, where the pressure is greatest, you need to lay down a large 1” seam on the bottom pane with a seam extending ½” up the inside of the vertical glass panes. Or at least that worked for me.
The biggest concern for glass is bowing under pressure, technically called deflection. The amount a piece of glass is going deflect is based on the dimensions of the glass. The most important factor in the pressure that is exerted is the height of the water behind the glass. The most important factor in the amount of bowing it will do is the thickness of the glass.
I could talk at great length about this, but I will just provide these guidelines instead.
1) If you build a standard 75g tank, 48” wide by 22” high or so, ½” thick glass will work.
2) If you build that same tank, but make the sides only 3/8” wide, that should work.
3) If you build that same tank, but make the long 48” front and back with 3/8” glass, it will probably work, but it will bow so much you’ll wish you never did it. And you’ll be scared to leave it full of water in your house. Or so I am told.
Me, I used ½” glass all the way around, and my deflection is only 1.5mm on both of the large panes. Much more than that, say approaching 3mm, and you need to worry. In my reference sources I link to a number of sites that deal with this, since bowing is probably the most critical consideration in glass aquarium building. Next is the choice of silicone IMO.
When you order your glass, make sure you get a company that can polish the edges with a machine. If they just snap the glass and hand polish it, you will get ugly rippling, wavy lines on the cross sectional surface of the glass. Machine polishing removes this.
Also these same machines can usually bevel the glass for you, which makes for a much nicer looking end product. If you get it, you’ll be happy you did.
Silicone is really, really difficult to remove from glass once cured. So you want to put masking tape over every inch of the glass that is not going to be siliconed. This is going to take a lot of time, and you will find it frustrating. But until you spend hours removing silicone from the glass, you’ll have to take my word for this… it’s worth the time. It also helps protect the glass from scratches in the assembly process.
If you are experienced at applying silicone (you know who you are), you only need to mask edges, rather than the whole glass surface.
No matter what you hear to the contrary, don't pull up masking tape unless the silicone is within minutes of having been applied. After that, it HAS to be fullycured, or you risk ripping the curing silicone up off the glass surface.
When you do remove the masking, after curing is complete, be sure to run your finger along the silicone seam, pressing down just at the spot where the masking tape is pulling away from the glass. This will prevent any silicone on the masking tape from pulling up silicone from the glass as it separates.
You will need to assemble the tank on a raised surface, like a tabletop. Your glass will be very heavy, and bending down to lower the glass to a floor level surface will significantly increase the difficulty of the assembly process. Also raising the glass over waist level will also create problems.
The surface will need to be very, very flat, and very sturdy - vibration free. I assembled mine on a raised redwood outdoor deck, and I’m certain that some of the leaks I sprung during testing (requiring removal , cleaning, and resiliconing of glass) was directly contributed to by assembling on a vibration sensitive, less than flat, surface.
Preparation, Planning and Execution
A lot of work should go into getting ready for assembly. This includes:
1) Detail discussions and precise, written instructions to the glass cutters. It included allowable tolerances, or variance, in the precision of their glass cutting. Make sure the toloeances you will acccept are in writing. To a company that makes glass for windows or shower doors, a 1/16" variance is pretty good work. To someone trying to make an all glass aquarium, it could be a show stopper. You want variances of 1/32" or smaller.
2) Elaborate edge masking. This even included constructing or finding a small tool to slide along glass edges as a guide for a consistent distance from edges. I found a small cabinate hinge, that when slid along the edge of the glass, it provided just the right distance from the edge for masking.
3) I built a small "throw away" test tank as a learning/practice exercise. I would strongly suggest this to anyone. Learning the basics of assembly and silicone application on hundreds of dollars of glass is a risky learning experience in my opinion. Give the whole thing a try on $30 worth of glass first to see what you are getting yourself into. It gets a lot harder when the glass gets bigger and heavier.
4) Before assemble of any given panel (piece of glass), every step was planned, explicitly written down, and discussed with the people providing assistance. Nothing was rushed or unplanned.
5) Because the actual application of silicone, and preliminary clean up of edges that has to be done very quickly before hand, every step of putting on a glass panel should be practiced immediately prior to actually doing it - sometimes multiple times. This means timing the speed of laying down silicone beads, putting glass in place, attaching clamps, and practicing wiping away excess silicone. When siliconing your actions need to move like clockwork. When you’ve already laid down a bead of silicone, it is no time to figure out you can’t heft a piece of glass, or that a clamp isn’t going to fit, or that an extra tube of silicone is not handy (or the scissors to cut the tip off with!)
6) Time your practice sessions. Laying down silicone and placing the glass in place MUST take less than 5 minutes, and the entire process involving clamping, ensuring everything is square, and wiping away excess must come in under 10 minutes.
The clamps you will need will change with each side you build. Apply clamps as follows:
Backside attached to bottom, no other sides
Use a cabinet right-angle clamp at each end on the bottom to hold the back perpendicular to the bottom, and use two J-clamps to press the side down onto the bottom.
Properly clamped backside
Attaching the small sides to the bottom and the back
For each of the two sides use a cabinet right-angle clamp to hold the side at right angles to the back. And use two J-clamps to press the side down onto the bottom. And use two more J-clamps to compress the side panel against the back pane
Attaching the front pane
Use four J-clamps to compress the front pane to each side panel. That’s two J-clamps per side. Also use a cabinet right-angle clamp at each end on the top to hold the front perpendicular to each side, and use two J-clamps to press the front down onto the bottom.
Example of HOW NOT(!) to attach the front pane
I had to replace this pane because of I used an orange strap clamp (see it around the top?) instead of spending the extra money to get the two more J-clamps I should have used to press the top of the front to the top of the sides. In this shot you can also see how the cabinate clamps are used to keep the top square with the sides.
And here is that same front side being reattached - clamped correctly this time
Tightness appears to be critically important in clamping. Don’t use strap clamps – they cannot exert enough pressure. I wish I could provide clear guidance on how hard to crank down on the J-clamps. But about all I can say is that they need to be tight - nice and snug. Or just a bit of effort beyond what is referred to as “finger tight”. But if you really crank down on the clamp you will squeeze out ALL the silicone, and that can be almost as bad as not tight enough.
When putting the panes of glass on you will want to do the following to ensure you get a good seal between the panes of glass. And by “good” that means sturdy and bubble free.
1) Use LOTS of acetone to clean every surface to be siliconed immediately prior to laying down the silicone beads. How much is lots? If it is dripping silicone, that should be enough. Use a lint free cloth and a bit of elbow grease to clean the wetted surface, and a dry lint free cloth to mop up the excess acetone. Give it a minute or two to evaporate.
2) Squeeze large, wide beads of silicone on the glass – lots of excess. If you use an entire tube of silicone for one large 48”x22” piece of glass, you’ve only used just a little too much. If you only used ½ a tube for a large piece of glass, use more next time. The key is to lay down excess silicone and so that you have to wipe up big gobs of excess after the glass is in place.
3) When you set a pane down on the bottom piece of glass, set it down at about a 25 degree angle, and sloooowly tilt it up to avertical position.
In terms of order of assembling panes, use the following considerations.
1) The bottom goes down on the work surface; everything will be built on top of that.
2) Only one piece of glass goes up at a time, two days between each of the four vertical panes of glass. Longer if the humidity is very low.
3) Start with the piece of glass that is going to be the long backside of the tank first. Then two days later, apply a side, then the other, and finally finish up by putting on the front.
4) For every place where a vertical pane rests on the bottom pane, apply the silicone for the bottom seam to the bottom pane, not the vertical pane.
5) For all vertical seams, place the vertical seam on the pane being applied, not on a pane already on the tank. This seems to reduce bubbles in the silicone. I don’t know why.
Once a pane is in place, one person needs to gently hold the glass in place (the silicone will help) and put one or two clamps on loosely. Then use your square to make sure everything is at 90 degree angles, gently making adjustments as required. Then put on the rest of the clamps, "finger tight" only. Once all clamps are on, tighten them down, alternating sides (first tighten a clamp on one side, then one on the other – back and forth) until done.
Once all clamps are on, begin wiping away excess silicone. If you have masked properly your thumb should work great to push away the excess. Have someone standing by with paper towels to clean your thump off often (there will be a lot of excess silicone). A waste basket will need to be near by to drop in the messy paper towels.
For the huge bottom inside seam on each pane, go ahead and treat it like all the other seams, wiping away the excess. Once all seams have had their excess removed, then go in and lay down a big bead again on the inside edge of the bottom. Yes, I know the little seam may have “skinned over”. That’s OK. Silicone sticks great to silicone, so the stuff you are squirting on top if it will bond well with the original seam. Then do the best you can to smooth out the excess silicone on the new big seam with your thumb – paper towels at the ready.
I’m told that by wetting your thumb with water that it makes a nicer seam, and the silicone is less inclined to stick to your thumb. You can try it, but it didn’t work for me.
This unfortunate shot was made possible by several factors:
- Making small seams with commercial grade silicon. Making tiny seams safely requires professional grade silicon.
- Inadequate claming - didn't use enough clamps.
- Tesing on a vibration prone surface.
- No styrofoam underneath the tank.
shouldn't have to repeat my mistakes - you can from them instead, just as I did.
If you do have to remove a glass pane for replacement, use an Exacto blade to cut it away. But if the seam is too small for that, don't try to wedge an Exacto in there. It scratches the glass, and can even chip it - I know. A very thin piece of steel wire works much better. You can find this in a hardware store for hanging picture frames.
Removing silicone from glass
1) If you have to remove cured silicone from a pane of glass, be prepared to spend many hours getting it perfectly clean, 8-12 hours for a large pane of glass – or only ½ that if you have a Dremmel.
2) Use a razor blades to get up a much as possible. Change blades VERY often, and keep scraping with a sharp blade until nothing is left but a silicone film.
3) Then use acetone and dust free cloths to rub away that fim. But that can take hours.
4) To dramatically reduce the time in removing the silicone film left over after the scraping, use a Dremmel tool (if you are lucky enough to have one) with a felt polishing pad.
5) The dust and film residue left over after the Dremmeling comes up real easy with mineral spirits, followed by a quick hit with the acetone, and you've got marvelously clean glass, at minimal effort.
6) If you are trying to get that residue film up, and don’t have a Dremmel, don’t waste your money on "Greased Lightening", "Dirtex", "De-Solv-it", or "Goof Off". None of it works as well as Acetone and elbow grease.
7) Also, be warned – If you spend enough hours with a razor blade in your hand, you are going to cut yourself. Count on it.
Removing masking tape
The longer masking take stays on glass; the harder it is to get it to come off clean. And expensive masking tape comes off cleaner than cheap masking tape.
Curing the silicone before filling
Curing time improves substantially in high humidity, and reduces in low humidity. At 50% humidity, I would advise waiting 5 days after I laid down my last seam before filling the tank.
If the seams feel hard to the touch, meaning you can't leaves a finger nail impression easily, then you should be able to add a bit of water. Fill it with about 1/8" inch of water in the bottom and the humidity will help it cure faster.
And if there are any questions about whether your tank is cured, smell the thickest and/or newest silicone. If you can detect that vinegar-like smell (at all), it’s not cured.
If you allow a silicone bead that goes between two pieces of glass to “skin over”, or form a slight film on its surface before you press the glass together, you should prepare for that seam to fail under pressure. Generally that means that you MUST press the glass in place within a few minutes of laying down the silicone bead. IMO 2 minutes is safe for the professional grade silicons I reccomended earlier, 5 minutes for commercial grades. Any longer and you are accepting an element of risk.
Filling and Testing
I believe you MUST have a piece of Styrofoam under your tank. And that your tank must be on a flat, level, vibration free surface.
Moving the Tank
Having two full grown, level headed, strong people to do the lifting and moving of the tank is a piece of cake. Having a wife and kids help you move it, as I did on occasion, is just begging for trouble. Your tank will be both fragile and quite heavy.
How long until I know it won't leak?
I don't know, maybe 10 years?
But I do know that in my learning experience I sprung multiple leaks (from my mistakes). Almost every one happened with 24 hours. The one exception happened after 5 days. But that was because I had the tank on a vibration prone deck, and the night it sprung a leak we were running back and forth to across the deck. I believe that was more of a stress induced leak, caused by unstable flooring and inadequate padding under the tank. In a vibration free, correctly padded setting that tank would have never sprung a leak IMO.
In conclusion - 24 hours is the magic number. Butif you are paranoid (like me) leave it full for 7 days before you really trust it.
Keep in mind, your tank is not reinforced. It’s just held together by silicone. So if you are using shims to level your stand, you are going to have to do it gradually and gently. Start with an empty tank, then adjust when ¼ full, then at ½ full. Get it perfect at that point. Jarring your stand around after that just puts too much stress on the tank IMO.
Make sure you really level your tank very well, especially side to side. Since there is no rim at the top to hide a small tilt of the tank. Any tiny amount of tilt will be quite noticeable – especially if it is side to side. Front to back level problems are a little less noticeable.
More information on silicone
I spent an hour an hour on the phone with an industrial application silicone guru at GE, and got the real low down on silicone. Here are some fun facts from that call:
1) No manufacturer will tell you their silicone works underwater, since they all degrade underwater over time. Only someone OEM'ing silicone will make that claim.
The Problem with Bottom Bulkheads
2) Silicone's primary strength is to itself, not what it is bonded too. So if it starts to pull away in a spot in an aquarium, it is almost certainly not going to "snap" with the tension, creating only a small leak. It will hold together in one piece and if more pressure is applied will continue to tear away from the glass instead, creating a potentially catastrophic leak instead.
3) GE’s SCS1200 has their highest adhesion strength, twice that of their commercial grades, and an unspecified amount over their consumer grades.
4) Silicone's adhesion strength in general does not approach its tensile strength. If you lay down a bead on top of some glass, you will be able to pull it up much easier than getting it to snap while pulling it.
5) The aquarium application requires silicones weakest strength, adhesion. This explains why all tank manufacturers all lay down a nice wide seam along the bottom edges of the tank. That's not just to fight water pressure, that's also to provide more adhesion surface to keep the bottom edges from ripping apart.
6) Silicone bonds very well to silicone, but much less well to anything else... like glass.
7) SCS1200 will only cure to a 1/4" depth. So under 1/2" thick glass, there can be no excess on either side while it cures. And that is 5 days at 50% humidity - more days if the humidity is lower.
I built tank with bulkhead holes in the bottom to facilitate water flowing into/out of the tank without visible equipment. While I know that will not affect most people, I thought it was worth passing along some of the consequences of that decision.
1) Everyone makes tanks with tempered glass bottoms, so bottom bulkheads almost certainly mandates custom tank building for many tank sizes.
2) The hardware adds cost
3) Having the holes drilled can add very significant cost. Or if you drill them yourself, significant risk.
4) I'm told it destroys the resale value of the tank.
5) Any padding, or support (Styrofoam, boards) under the tank have to have matching holes cut and/or drilled. So getting a new board is a PITA.
6) The hardware takes a lot of space under the tank that must be accommodated. In my case, it also meant that I had to remove the drawers from the stand (drawers would have been nice).
7) They limit aquascaping options. You've got equipment to hide. But more holes increases your flexibility.
8) You significantly increase your opportunities for leaks.
9) Moving your tank involves a potentially non-trivial disassembly process. It's not as imple as drain the water, pull out the hoses and move.
And for everyone of these factors, except for #1 and #7, it gets worse in direct relation to the number of bulkhead holes you have.
Bottom Bulkhead Lessons Learned
1) Install the bulkheads before you put the tank in the stand. Much easier! 4"x4" posts work well as supports for the tank so you can work above it and have room below for tightening the bulkheads.
2) Plastic bulkheads can break if over tightened. And since they have to be very tight, you don’t know how tight “too tight” is until you break one. Having 1 extra bulkhead around can be a lifesaver if that happens.
Lot's of people build tanks like this all the time. And for them I'm sure this is pretty easy. But without very proscriptive instructions, I found this to be a bit difficult and daunting. But certainly possible, and immensely satisfying once complete.
My advice is to be constantly aware of the danger - even professonal glass fabricators don't like handling such heavy untempered glass. One small slip, with a piece of glass breaking the wrong way and a bit clumsy handling could lead to very serious injury, or even death. Be careful.
I also advise humor and perseverance. If you are doing this for the first time, it may not go exactly as you expect. Expect the unexpected. And don't give up if you have to spend a bit more time on your construction project than you anticipated. But hang in there. Keep your sense of humor at the ready, and you'll have something beautiful that you can be proud of before you know it.
My best information sources were Tom Barr of The Barr Report, and Del Goins of AquariumPlant.com.
But I got lots and lots of really good advice from my friends at PlantedTank.net. Thanks folks! I could not
have done this without you.
Also the following internet sites were quite useful.