Is This Structurally Sound?

[AngryKoala]

Hi all,

I could really use your input here. Here’s what I’ve done so far…

I put some pine on an existing 65 gallon fish tank stand (a basic stand made by Sauder), and then stained the pine. The pine is just for looks (and it looks a thousand times better than the original). Now I intended on just setting the tank back on top and calling it a day, but that would be too easy

What I’d like to do is lay down a sheet of ¾” plywood, lay some pressure treated wood on top, and then another layer of ¾” plywood on top of that… and then set the tank down.

#1 - http/qwerty71.wave.prohosting.com/Stand_001.jpg

In #1, you can see the original stand on the inside… the pine just covers it up. The original stand is what the tank used to sit on, and it’s pretty obvious in the picture.

#2 - http/qwerty71.wave.prohosting.com/Stand_002.jpg

In #2, I’ve set down some plywood and the rows of pressure treated wood on top. I still need to cut the wood to make sure it’s evenly cut and that they’re all the same length… but you get the idea.

The pressure treated wood needs to sit half an inch away from the edge of the plywood because it too will be covered by pine. And THAT’S what makes me nervous. Because underneath the pressure treated wood is the plywood… directly underneath that is nothing since the plywood is only resting on the original stand, which is only half an inch thick.

I was also thinking of putting more pressure treated wood in the corners of the tank under the plywood to also help support.

Any suggestions/warnings/comments would be greatly appreciated.

Thanks in advance,
- Sam

 

[nicklfire]

pics not working

 

[AngryKoala]

Sorry about that... no idea what happened. I uploaded them again and reset the permissions.

Give it another shot.

Thanks,
- Sam

Actually... if you copy and paste the image URL to another browser, it works... it doesn't work via the link for some reason.

- Sam

 

[blue_ram]

[snip]

What I’d like to do is lay down a sheet of ¾” plywood, lay some pressure treated wood on top, and then another layer of ¾” plywood on top of that… and then set the tank down.

May be I'm not seeing your objective, but unless you went from glass aquariums to acrylic, I don't see any benfit of what you're doing (aside from increasin the height of the stand). The glass only needs to be supported along the EDGE of the bottom surface, while the acrylic needs to be supported on the ENTIRE bottom surface. This means, the stands for the glass needs to be perfectly straight. Glass don't tolerate surface irregularity along the support too well. My only concern is that the plywood supported by the treated lumber won't be perfectly flat.

The pressure treated wood needs to sit half an inch away from the edge of the plywood because it too will be covered by pine. And THAT’S what makes me nervous. Because underneath the pressure treated wood is the plywood… directly underneath that is nothing since the plywood is only resting on the original stand, which is only half an inch thick.

Yes, but isn't the inner panel (MDF?) glued to the 1/2" outer wood panels? Then this shouldn't be problem unless you get the MFD wet.

I was also thinking of putting more pressure treated wood in the corners of the tank under the plywood to also help support.

Again, putting support only at the corners won't help at all, since glass needs even support all along the bottom edge. If you want to raise the height, why not do this on the BOTTOM of the stand. Woods are more forgiving than the glass.

 

[AngryKoala]

Yup, the goal is to raise the tank itself, and have drawers built underneath between the rows of pressure treated wood. Also, the tank is glass... sorry, I should've mentioned that.

Since plywood does have irregularities, I could use MDF instead to ensure a flat surface... I wasn't sure if a sheet of that could handle the weight. Can it?

But regardless of what I use, the outer half inch of the bottom sheet will be the only thing making contact with the original stand. Since the pressure treated wood won't be going all the way to the edge of the sheet, I thought adding columns underneath would help support everything.

- Sam

 

[Lateral Line]

I can't see the pictures either way. Whatever you are trying to do, I'd be very wary of using MDF. Even small water spills can turn it to a mush.

 

[blue_ram]

Yup, the goal is to raise the tank itself, and have drawers built underneath between the rows of pressure treated wood. Also, the tank is glass... sorry, I should've mentioned that.

Since plywood does have irregularities, I could use MDF instead to ensure a flat surface... I wasn't sure if a sheet of that could handle the weight. Can it?

But regardless of what I use, the outer half inch of the bottom sheet will be the only thing making contact with the original stand. Since the pressure treated wood won't be going all the way to the edge of the sheet, I thought adding columns underneath would help support everything.


- Sam

Ok, now I understand what you're trying to do. What ever you do, don't use MDF for this. I like MDF and use it for just about everything except for aquarium stands and hoods. Although you could use it (with some care) for external panels for the stands. With some exotic veneer, and shallec, it can look incredible.

Any way, back to your problem... You MUST add columns AND horizontal beams for support. Without it, the aquarium is only supported at the contact points between the 4x4 and the original support. The plywood adds next to no support. So if your aquarium is 48"x13"(wxd), then your support points are reduced from (2x48"+2x13")x1" = 122 sq in. to (6x4")x1" = 24 sq. in. This means 700lbs+ of weight must be supported by 24sq. in of glass.

The cheapest way that I can think of doing this would be using lots of 2x4 as support beam AND 2x3/2x4 laid on top of the 2x4s. You don't need any plywood at all. It's adds weight, provides virtually no structural support, and you probably won't be able to see them anyway. If you can't use lots of 2x4 columns, then use the 2x3 on it's side. Remember, the aquarium pushes down with 700lbs of force, so the stand must push back with equal force in opposite direction. That means, the supporting structure must not give (i.e stiff).