What to use to seal plywood tank?

I personally use the epoxy pour method, but wouldn't consider it high on the affordability scale.

I too am going to build a plywood tank. After much research I found that my biggest concern was using a product that would allow me to silicone the glass to it without failing. From what I gathered west systems epoxy will not only allow me to do that. It will also let me apply a final coat of tinted Sweetwater epoxy that also allows silicone adhesion. I am still in the planning stage and have a plate of glass 6 ft by 20 by .5 from my cracked aquarium so I will attempt to do a thread with pics and maybe video when I get started

When I built my 750 gallon plywood I put 4 layers of fiberglass with mat in all the joints. I rolled fiberglass resin on side walls for two coats, lightly sanded, then rolled two coats of Sweetwater epoxy on top. Been running for 3 years now with two viewing windows.

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I have been doing a lot of re search also. Epoxy is tried and true. I am going to use liquid rubber.

Epoxy I feel you must have a very sound build with no flex in order to get many years, must be applied properly, mixed perfect and applied perfect, smells and I have a concern which might be nothing but how the tank light can effect the epoxy since epoxy has zero tolerance to UV which breaks down the epoxy, if some one can give there two cents on that.
GFlex by west systems is probably the best right now for Aquariums as it has a lot of give. Epoxy is brittle.

Liquid rubber can last a very long time flex and be smashed and dented and super easy to apply with low oder! It is used for coating ponds and all kinds of tanks from potable water to other liquids.

Harder to screw the stuff up and 3m 5200 or Tremco Butyl Sealent will secure the window from what I hear

Max ACR epoxy going on 3 years with zero issues. Fiberglass mat in the corners only for me. 500 gallons 6ftx4x3 cost roughly $120 to seal including the cost of the black tint and shipping.

CANAMONSTER said:

Epoxy I feel you must have a very sound build with no flex in order to get many years, must be applied properly, mixed perfect and applied perfect, smells and I have a concern which might be nothing but how the tank light can effect the epoxy since epoxy has zero tolerance to UV which breaks down the epoxy, if some one can give there two cents on that.
GFlex by west systems is probably the best right now for Aquariums as it has a lot of give. Epoxy is brittle.

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epoxy has zero tolerance from UV.... That isn't completely accurate. Firstly, there are plenty of UV resistant epoxy resins out there. They just cost a little bit more money. About $110-150 per gallon. Even with the regular epoxies, which are about $80+ per gallon, once you add an opaque colorant to them, that will help block any UV from penetrating it. For aquariums, the water itself reflects/absorbs much of UV light and protects the epoxy from drying out. So it would take a massive aquarium lighting system and many many years to damage a colored epoxy coating. There are quite a few 5+ year old epoxy resin tanks from folks here at MFK. There are probably some 20+ year old tanks that are coated with epoxy resin. Many of the fake aquarium corals/decorations are made from an epoxy resin. For UV damage to occur, the epoxy would need to be exposed to direct lighting, where it was baking for many hours per day. 1st it would start yellowing, then it would become completely bone dry and start cracking, then lastly it will delaminate. Obviously, in a water filled aquarium it will never reach the stage where it becomes completely bone dry below the waterline. If anything above the waterline is clear epoxied, then maybe you'll run into problems. The most critical spots are usually the end grain of the plywood on the top or the bracing, and the exposed parts just above the waterline where it may dry out.

How about its brittleness

CANAMONSTER said:

How about its brittleness

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It's not brittle like glass, if that's what your asking. It's more like acrylic. But when epoxy is used in composition with something like fiberglass cloth, it's quite durable, hard, and very strong, especially for it's weight. If you used Kevlar or carbon fiber instead, it would literally be bulletproof. Epoxy resin is one of the most versatile materials there is. You can build about anything with it. You can use it for sealing, bonding, casting, or fiberglassing.

Not all epoxy smells bad either. The one I've been using is practically odor free. Very low VOC.