Hybrid plywood tank question

[jepuskar]

Attached is my current tank build. Bottom and back panels are plywood, reinforced with bondo. There is a 4" lip going around the 3 bottom viewable sides and a 4" lip on each back side.

The plan is to install 1/2" tempered glass, 29" high and silicon to the bottom lips and also at the back on the 2 side lips and of course between the glass seams using the injection method.

I will also have glass eurobracing installed.

Seeing the side panels will not be directly attached to the backpanel, but will only be siliconed to the side lips, is there anything inherently wrong with this design? I'm just having doubts about my design now that I'm getting close to installing the glass.

 

[Backfromthedead]

I've drawn up plans for similar type tanks in the past but never went through with them. Your lip design is pretty much how I resolved to treat the bottom.

It appears that there's just a single layer of 3/4 ply for the back panel. Is it reinforced with a frame of any kind behind it? If not, I would consider doing so before moving forward. At 29" high and I'm guessing 60-72" long the plywood will flex, possibly even break open once it's full. Even eurobracing along the top probably won't do much to hold since silicone does not form nearly as strong of a bond to wood (or epoxy-coated wood) as it does glass. If it flexes, it will eventually open a seam, most likely right in the middle.

If it was me, I would've left the front wood lip off before construction, then laid in the glass and liberal silicone before screwing the lip on tight, using it to effectively brace the tank while it sets up. But you may have an equally effective workaround to this.

1/2" tempered should work but I would want thicker at 29" height. Always want thicker lol. Most panels that size should be 5/8" or better. An effective eurobrace will definitely help though.

can you go over some of the other materials used like epoxy type and silicone you're planning?

 

[jepuskar]

I've drawn up plans for similar type tanks in the past but never went through with them. Your lip design is pretty much how I resolved to treat the bottom.

It appears that there's just a single layer of 3/4 ply for the back panel. Is it reinforced with a frame of any kind behind it? If not, I would consider doing so before moving forward. At 29" high and I'm guessing 60-72" long the plywood will flex, possibly even break open once it's full. Even eurobracing along the top probably won't do much to hold since silicone does not form nearly as strong of a bond to wood (or epoxy-coated wood) as it does glass. If it flexes, it will eventually open a seam, most likely right in the middle.

If it was me, I would've left the front wood lip off before construction, then laid in the glass and liberal silicone before screwing the lip on tight, using it to effectively brace the tank while it sets up. But you may have an equally effective workaround to this.

1/2" tempered should work but I would want thicker at 29" height. Always want thicker lol. Most panels that size should be 5/8" or better. An effective eurobrace will definitely help though.

can you go over some of the other materials used like epoxy type and silicone you're planning?

Hi and thanks for the detailed reply. I've included some more pictures. I have a 2x4 wrapped around the entire base of the tank, 2x6's behind the side lips overextending to the back, where I put a 2x8 on top of the wrapped 2x4, and then added another sheet of 3/4" plywood cut out for my external overflow.
The eurobracing is also 1/2" tempered glass x 4" wide.

Just picked up the glass and the bad news is they cut the front piece too long by 1/16" of an inch, but the good news is, after doing the resin etc etc, my opening for the front glass shrunk from 70.5" to 70 7/16" , so since they screwed up the cut, they will redo it and this time I will ask for 70 7/16.

The entire tank is covered in fiberglass matting with bondo resin and 3 coats of Pond Shield. The silicon for everything will be ASI's RTV.

The only other thing is this is meant to be a built in wall tank with 3 sides viewable, so there will be a wall built around the three sides....I could technically silicon the studs to the top of the glass or at least have them rest up on it, but I don't think that is a good idea..I really don't want the wall to be bonded to the tank like that. I could just build the wall out a little and support the top of the tank differently or not at all.

This is more of a improvise as I go....otherwise the project will never have been started.

 

[M1A1]

Hard to argue with anything you've done or are planning. Thicker glass is always nice, more fiberglass is always nice, more bracing is always nice. ?

I wouldn't silicone the glass to the studs (or drywall) either, just build it close and fill the gap with some weather stripping, foam tape, or backing rod.

Are you doing a Modular Marine or similar type of internal/external acrylic overflow?

 

[jepuskar]

Hard to argue with anything you've done or are planning. Thicker glass is always nice, more fiberglass is always nice, more bracing is always nice. ?

I wouldn't silicone the glass to the studs (or drywall) either, just build it close and fill the gap with some weather stripping, foam tape, or backing rod.

Are you doing a Modular Marine or similar type of internal/external acrylic overflow?

Thanks Jack. I have a Synergy Reef Ghost Overflow, that is what the back plywood was cut out for anyway..hopefully accurately.

My main concern is that the side glass panels won't be attached to the back wall of the tank, but just the side vertical lips and about 1/2" from the back wall. I tend to over complicate things in between my ears, but when filled with water, assuming everything is square...there is an equal pressure on the bottom of the tank and an outward pressure against all 4 sides, right? For some reason, I think with this design the pressure would pull the front glass forward and take the side panels with it...at least that is the mental image I have. I don't think that is how it works, but I just see it in my head.

 

[Backfromthedead]

Hi and thanks for the detailed reply. I've included some more pictures. I have a 2x4 wrapped around the entire base of the tank, 2x6's behind the side lips overextending to the back, where I put a 2x8 on top of the wrapped 2x4, and then added another sheet of 3/4" plywood cut out for my external overflow.
The eurobracing is also 1/2" tempered glass x 4" wide.

Just picked up the glass and the bad news is they cut the front piece too long by 1/16" of an inch, but the good news is, after doing the resin etc etc, my opening for the front glass shrunk from 70.5" to 70 7/16" , so since they screwed up the cut, they will redo it and this time I will ask for 70 7/16.

The entire tank is covered in fiberglass matting with bondo resin and 3 coats of Pond Shield. The silicon for everything will be ASI's RTV.

The only other thing is this is meant to be a built in wall tank with 3 sides viewable, so there will be a wall built around the three sides....I could technically silicon the studs to the top of the glass or at least have them rest up on it, but I don't think that is a good idea..I really don't want the wall to be bonded to the tank like that. I could just build the wall out a little and support the top of the tank differently or not at all.

This is more of a improvise as I go....otherwise the project will never have been started.

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Gotcha, if you weren't planning to already, I would still screw down something like a sealed piece of plywood as a brace on the top of that back panel to help support it, running screws into the entire length.


Even with the fiberglass it couldn't hurt to shore it up a little more.

One more thing, if at all possible and you have more pondarmor, I would put at least one coating on the back of the tank. Maybe even just a latex paint would help. Although it's supposed to stay dry back there, you'll inevitably get some splashing at some point and you don't want want to risk water accumulating between those ply panels and rotting. I know it seems like a long shot but better safe than sorry in this case.

The biggest reason I never did attempt a tank like this was that I couldn't put confidence into the back panel design and relying solely on the silicone to epoxy to hold the glass in place. I'm not saying you should alter your plans at all, but if I ever do attempt it, I will probably try a coated lumber top brace around the entire tank that is securely mounted onto the back panel. This could be mounted after your glass eurobrace and would alleviate your concerns about the glass pitching forward in my mind at least. I made a similar brace coated with flexseal for my most recent glass build that has worked well so far.


Anyways, best of luck moving forward. I look forward to seeing your progress.

 

[jepuskar]

Gotcha, if you weren't planning to already, I would still screw down something like a sealed piece of plywood as a brace on the top of that back panel to help support it, running screws into the entire length.
View attachment 1495401

Even with the fiberglass it couldn't hurt to shore it up a little more.

One more thing, if at all possible and you have more pondarmor, I would put at least one coating on the back of the tank. Maybe even just a latex paint would help. Although it's supposed to stay dry back there, you'll inevitably get some splashing at some point and you don't want want to risk water accumulating between those ply panels and rotting. I know it seems like a long shot but better safe than sorry in this case.

The biggest reason I never did attempt a tank like this was that I couldn't put confidence into the back panel design and relying solely on the silicone to epoxy to hold the glass in place. I'm not saying you should alter your plans at all, but if I ever do attempt it, I will probably try a coated lumber top brace around the entire tank that is securely mounted onto the back panel. This could be mounted after your glass eurobrace and would alleviate your concerns about the glass pitching forward in my mind at least. I made a similar brace coated with flexseal for my most recent glass build that has worked well so far.
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Anyways, best of luck moving forward. I look forward to seeing your progress.

Thank you again for the feedback. I have some liquid rubber I was going to put on the back and yes, I also thought of putting a brace across the top like that. I'll do that after I get the overflow installed.

I'll need to think about the top trim piece and how to tie it into the existing plywood. Maybe I can use heavy duty right angle brackets to screw it into the side lips. I''ll figure it out. I have time, need to go return this glass piece. Thanks again for the feedback.

 

[kzimmerman]

When you put in the bracing, try to screw the 2x4's on the side, that way you get the most bracing possible. The way you have them screwed in flat like that is not as strong. Since you are doing the back in plywood, you could put the bracing on the inside of the tank as high as you can get it, just under the overflow. You can use scrap plywood for this, or even something like a 1x4 or wider board, not pine or cedar. Poplar is probably sufficient. Screw from the outside, then coat the whole works. This also gives you a shelf at the back of the tank that you could use for aquascaping, growing marginals, whatever. The idea is that it can't flex outward. The glass can be braced in the same way, on the top rim of the tank, using glass.