large tank construction/repair HELP!

[saltydog]

I am STILL in process of fixing my 350G tank which needs new bottom. I have located some 1/2" salvage glass which is 3/4" too short to use as a bottom with vertical sides of tank SITTING ON bottom but could be cut so that it would fit INSIDE of the 4 aswembled vertical sides. I have questions:
1) In terms of structural strength what would be the ideal amount of space to leave at the glass joint between the edge of the bottom pane & the sides of the vertical sides?
2) My plan is to set the bottom pane on a table & then set the 4 assembled sides around it. I will then squeeze the silicone in place. (I will apply the "internal" silicone beads later. Will this work or will I end up with air bubbles which will cause the structure to be weak?
3) I would put polyethelene plastic sheet on tabletop to stop silicone from adhering to table top while silicone is setting. Does silicone adhere to this? If so, what other material should I use to prevent this from happening?

Thanks, everyone, who has suffered to understand my plans for this project. I would appreciated your input.

Also, if there is anyone who is planning a custom tank construction then I may be able to secure you your glass at a good price. Let me know your preferred tank dimensions & I will get back to you about price & availability.

Both 1/2" & 3/8" (12 mil & 10 mil) salvage glass seems to be available. It appears to be in unscratched condition.

[Nelson]

350 gallons!!!!!!  Once you're up and running salty all you'll need is some scuba gear and you'll be able to get close and personal with your fish!!

[StylinT]

silicone does adhere to poly but a good technique we use on the job site when caulking windows is spit on your finger an wipe the caulking once your bead is on the glass it will smear the silicone into any places the initial assembly missed

as for structural i dont think it would be to strong if the bottom fits in the middle on small tank i can see that working cause there isnt much stress on the bottom of the tank but on large tan with alot of water say 350 gallons i think the wieght would push the sides out an eventually break the seal but ya could reinforce that by building a small wall around the bottom of the glass to hold the walls

i dont know how ya planned it all out but this is my opinion an just that im not a professonal tank builder i just uild houses lol hahaha
hope this all helps

[saltydog]

I have learned that it is not possible to replace a tank bottom by insetting it into the sides as the tolerances are too critical to ensure using only a thin layer of silicone & one cannot clamp it afterwards. To repair a tank by means of an inset bottom one should disassemble the entire tank & rebuild from square one.

[BigDaddy]

Ouch, sorry to hear that.

So, are you going to tear the tank down and rebuild it, or give it up to the patron saint of lost causes?

[saltydog]

No, not giving up. Buying NEW glass of a size to replace bottom as it was-ie. under bottom edge of side panes. This will be MUCH more expensive for me, however. c'est la vie.

[artw]

why dont you just put a new piece on the bottom, that the 4 sides sit on?

[saltydog]

That's it-exactly what I am planning to do. Cost of  3/4" 30"x72" glass is $500 plus tax!

[artw]

Dude.
Why not use a thinner glass?
Discuss.

[saltydog]

In its present location where it is supported by reinforced plywood I could probably get by with 1/2" glass. But who can say for sure?  And if the tank were ever to be used in another application it might break. Usually the manufacturers make tank bottoms as strong or stronger than the sides. In the better tanks sides are float glass & bottom is tempered glass which is almost twice as expensive.

[StylinT]

What aboput if ya went to 1/4 glass an reinforced it with 1" plywood or 2 inches of plywood that should be alot cheaper an even more durable than 1/2 " glass but its just an idea im shooting at ya

[BigDaddy]

I wouldn't skimp on the bottom plate... from what I understand it is the most important structural piece of the tank.

How would you feel if 350 gallons of water ended up all over the place because you decided to go with glass that was 1/4 thinner?

I've seen all wood tanks before, with a window cut out at the front... but I've yet to see a hybrid tank like the one being proposed...

[artw]

but if your BASE, or stand, is strong enough to support everything inside the tank without deforming or bending the glass at any point,  why would you need to overdesign the bottom glass?
just imagine 4 pieces of glass siliconed to a concrete floor,  the concrete floor ain't going anywhere.
now if Salty can come up with a concrete floor,  then we're cooking with fire!

[james]

Hi Roger
You may want to consider using ply wood for your bottom piece of your tank. Eveen with the epoxy paint to seal I believe it will still be an cheaper alternative to glass

James

[StylinT]

im with art I think that f ya went with a 1" ply or even 2 inches of plywood lumberlocked (Glue) togethor that it will be just as strong as 1/2 " glass

[saltydog]

Thanks for the ideas for using plywood for a base. What if I did this?
-cut a plywood base 2 inches larger than the tank footprint & painted it with marine paint;
-set the tank on top of plywood & cut angle iron to set on the 2" lip all the way around the outside of the glass side;
-silicone the iron to the exterior of the glass sides & then screw it to the 2" lip of the plywood outside of tank (to stop tank glass from bowing when filled with water;
-seal the inside of the glass where the glass meets the plywood with marine epoxy.

Does this idea hold water?

[StylinT]

it sounds like it should hold water but why not put a piece of glass instead of using the marine paint
i only suggest that cause i have no expierance with marine paint