About 6 months ago, I built an aquarium wood table (stand). to build it, I used pine wood 0.63" sheets.

for 5-6 months it was great, though few days ago I noticed that the top sheet that the aquarium is sitting on it - getting bent. I can't understand what is causing this phenomenon! I was thinking maybe the material wasn't good or maybe there's too much pressure on this sheet, so I'm thinking of changing this top sheet to an oak 1" sheet.

what do you think about this problem? how can I solve it? I attach pictures. thanks in advanced for advising,

links to video and pictures of the table:

  • Just a quick additional note about the finish 'sealing' the wood, do be aware that even with a very thick application indeed (six or more coats) you don't completely isolate wood from changes in exterior humidity. Film finishes do slow the uptake and loss of moisture, but don't provide a complete barrier as you might have thought.
    – Graphus
    Aug 2 '16 at 8:25
  • Some of the issue may also be based on where the aquarium is supported by the wood. If the tank does not have a flat bottom, it's putting all the weight on the pressure points. Are there feet at the corners of the tank? If so, that would cause the outer edge of the top to bend down since the weight is directly placed where there is no support.
    – FreeMan
    Aug 2 '16 at 21:27
  • @FreeMan the whole aquarium bottom is equal - it's flat. so the bottom of the aquarium equally touches all of the table
    – Ami
    Aug 3 '16 at 11:09

Judging by the pictures and the movie, I'd say the problem is just warping of the pine boards. The fact that the boards are straight at the center (where they are screwed to the vertical legs) and only the edges are bent suggests that.

It is possible that the aquarium environment is more humid than the rest of the house, making the warping worse. But this can also happen with low quality pine boards that were not thoroughly dried before dimensioning.

I would suggest replacing the pine boards with a high quality marine grade plywood (or at least a plywood sheet that will handle moisture better). If 5/8" pine is enough for the weight of the aquarium, 3/4" plywood should be more than enough, and you could probably go thinner (down to 5/8" or even 1/2"), depending on the full weight of the aquarium (plus water).

If you would like to avoid sheets and go with solid wood (I don't think that the actual wood selection will matter all that much), make sure to fully acclimatize the wood to the aquarium environment before assembly.

  • Another option would be to add vertical lengths of the plywood to stabilize the flat surfaces. Plywood is quite flexible along its entire length, but it quite a bit more rigid on its edge. Even solid wood would want to bow/warp if not joined and braced against the direction of the forces. Aug 1 '16 at 12:21
  • Eli lser and @BrownRedHawk thank you for your comments, I forgot to mention that aquarium weights 220 pounds. the pine 0.6" plywood I used was covered with few layers of lacquer to protect it from humidity. I'm not interested to add additional support at the sides of the table to support the edges of the top (bented) sheet because it will ruin the design of the table. will changing the currently bented pine plywood sheet to an oak 1" plywood sheet solve the situation? (and covering it with lacquer) thanks
    – Ami
    Aug 1 '16 at 12:41
  • With that amount of weight, I would go to something like a marine grade plywood, rather than just oak. All of these woods, even with lacquer will eventually want to give to the pressure, just as trees bend and sway in the wind. The ones that don't move are either GIGANTIC or, get broken and uprooted. It is possible to add metal bracing that would be invisible from a regular viewer though. It is asking too much of any but the most exotic sheet goods to flex without sufficient vertical support. Aug 1 '16 at 12:44
  • @BrownRedHawk so what can you recommend to do? I cant find a marine grade plywood here where I live.. what could be the best solution for this situation? thanks again
    – Ami
    Aug 1 '16 at 13:28
  • @Ami IME, I think working to use something like 1" steel angle attached to the underside, set back from the front end to avoid it being visible. Steel angle will provide much better resistance to sagging when paired with the wood. I did something similar for an entertainment center shelf holding a heavy head unit and amplifier. You can paint it dark to help keep it from being obvious. Aug 1 '16 at 13:50

Some guesswork is involved here as you've managed to take pics and shoot a video that don't show one or two key details of the construction :-)

The obvious first thought is what you're worried about, that the bowing you're seeing is due to this being made from pine. Although pine is quite strong if used the right way the tank does represent a very significant load and it may be too much for the thickness you've used.

However I think there's more going on.

Construction issues
There are additional concerns in relation to how this is constructed, with the vertical supports cross-grain to the top. As I was writing this I realised there are actually two problems with this, not just the one I first saw.

The first is common to all furniture with similar tops, where there must be allowance for the panel to expand and contract with changes in internal moisture level. As we can't see how the top is attached (if at all) to the upright panels it's impossible to tell if this is an issue.

Switching to oak wouldn't necessarily be a solution as a result.

I was going to write initially that if you changed to top to plywood (see Note bottom on plywood type) it would avoid these issues — there are no worries with cross-grain attachments and it is inherently stiffer so will naturally try to resist bowing under load. But then I realised the following.

The second issue with the uprights is not so obvious but is potentially just as serious if not more so as it's still a factor even if the top were switched to plywood. Being built as they are their axis of expansion and contraction is vertical so when those are expanded they will push upwards on the top. This wouldn't be a problem necessarily, except for the steel posts to either side.

And conversely when these uprights contract they will tug on the top downwards if they're attached securely to it. If on the other hand the top just floats on them when they are at their driest point they could shrink enough to leave a gap between their upper edges and the top, which of course could be a direct cause of it bowing downwards.

Note: although it's a good grade of plywood it shouldn't be considered necessary to use marine-grade ply in this application, as although it is around water there isn't the expectation that it'll constantly get wet.

  • Graphus, thank you so much for the detailed explanation. although there's a lot of information - I concluded not that much. from what I understood - the problem is about the uprights (the metal poles), they cause a pressure on the top board and that's what causes the bowing effect. I hope I understood well. I'm not sure I understood the first concern. will it be possible to solve the problem with exchanging the top pine board to a thick 0.6" steel board? please use simple English as possible because it isn't my native language. thank you so much!
    – Ami
    Aug 2 '16 at 14:29
  • Good observation. My guess would be that it is now summer, a time of high humidity, and the boards in the uprights are at there widest. If nothing is done, they will most likely contract to their narrowest n December or January and there will be no sign of "warping" in the table top
    – Ast Pace
    Aug 3 '16 at 2:51

I use to be a contractor and built car washes. In high moisture or soaking wet areas (even exposed) we use marine plywood. Its very attractive, so do not let the plywood part scare you off. It is what is also used in boats and takes stains nicely. Very durable, water and weight pretty much has no bad effect on it. It would require extreme abuse. Cheers

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