Large container to hold water for short-term exhibition

[Forest Kelley]

I'm an artist who would like to make container to hold water approximately 4x8' x 3" deep. It needs to last for only two weeks, so I'm not looking for a permanent water resistant surface, but I also don't want to risk having it leak during the exhibition.

Ideally i'd use something like a stainless steel photography darkroom sink, but I'm not sure I can find one easily. I'm open to all materials (MDF, plywood, plastic, paint, metal, etc.) but I'd like to be able to find them in town without special ordering. I'd also like to to look clean and not sloppy. And, I only want to spend a few hundred dollars at most.

Ideas that come to mind are:

• Painting MDF or plywood with oil-based paint or marine finish. I know MDF would fall apart quickly if it got wet. But would a good marine finish or oil-based paint prevent this for at least a few weeks?
• Painting a woven tarp with marine finish. I know tarps aren't waterproof on their own, but with a coating of marine finish, maybe it would make for a nice thin substrate with good tensile strength? Visually, I like the possibility of this option, though the sides would almost certainly need bracing which raises aesthetic questions.
• Lining with thin plastic could work, but I'm not sure it would look very good (wrinkly, etc). But it might work. It would also be prone to leaking if someone poked it.
• Rubber could work, but I'm not sure where I'd find such a large sheet. And it might difficult to make the corners look clean without cutting and gluing them back together (which might defeat the purpose). But maybe a strong glue would work adhere the cut corners?

Thanks!

[Sam Force]

Why not make a box out of 3 2x4s eight foot long. Place a big piece of plastic over the box, smooth out the wrinkles and corners. Then nail furring strips over the plastic to hold in place, trim the edges and be done. Cost would be minimal

[Jamie Buxton]

Make a frame from 2x4s standing on edge. Fasten them on to a 4x8 sheet of construction plywood or OSB. Get 6 mil plastic sheeting at any big box store. Drape over the frame and tack to the outsides of the frame. Fill with water. Done.

The sheeting is available black or clear. If the floor of your exhibit space is nice to look at, you could buy the clear, and leave out the plywood.

For belt-and-suspenders leak resistance, use two layers of the sheeting.

Hah. Sam types faster than I do.

[Malcolm McLeod]

That's a fairly minimal depth, so lots of options: if you stick with wood/MDF, coat the interior and top edges with Epoxy. It will easily last your 2 weeks.
Or, go see a sheet metal shop - they could solder & bend a galvanized tray to that size (if it meets your appearance requirements).

[George Yetka]

I would contact a sheetmetal fabricator. I get pans like that fairly frequently to put CRAC units in. for a couple weeks you may get away with galvanized for cheaper but SS wont be too much more. Im thinking it would be less than $1000. They may ask that you adjust size to be
3'x7' so they can make it out of a standard sheet. but they can get larger pieces.

5x10 sheet is about 500 then a few hours of fabrication

[Forest Kelley]

Wow, so many ideas! I do think that the sheet metal concepts would look the best. I'm not sure I can afford that, but I'll investigate.

The epoxy with MDF is a good tip. Do you think marine varnish would also work? Or is it riskier than epoxy? I feel like epoxy would work great for the edges but I wonder if it might be difficult to coat such a large surface with it?

I also appreciate the votes for 6 mil plastic sheeting. I worry it might be a disaster if it gets a leak, but I'll investigate.

Thanks again, all!

[Brian Tymchak]

Kind of along Jamie's post, take the same 2x4 and sheet good construction and instead of plastic, try a bucket of Flex Seal. 2-3 coats with heavier coats in the corners. Disclaimer - I've not done this myself.

[Gary Ragatz]

Kind of along Jamie's post, take the same 2x4 and sheet good construction and instead of plastic, try a bucket of Flex Seal. 2-3 coats with heavier coats in the corners. Disclaimer - I've not done this myself.

This was my thought, too. Maybe caulk the corners before the Flex Seal.

[George Yetka]

Fish tank guys use silicone. Not sure if it has any additives but aquarium silicone is on Amazon.

You could try that with lexan. Home depot has 4x8x1/8" lexan for the base and I would use something a little thicker for the sides. There isnt any real pressure at 3" deep. Its only .433 PSI of Gauge pressure per foot.

I still might think of using a 1x1 nailer of an engineered product to strengthen the corners

[Gary Ragatz]

As long as we're still kibitzing, I thought I'd ask about how the display is going to be supported. The water will be 720 pounds or so, add in the structure itself, and you're probably at 800 pounds (or more, if there's something heavy that's going into the water). If it's on the floor, no problem. If it's going to be elevated, you'll need to make sure there's adequate support beneath it to keep it from sagging. This might just mean 3 or 4 sawhorses.

[Scott Winners]

At 4x8x0.25 feet I come up with I come up with 8 cubic feet of water. I haven't been scuba diving for a long time but I think something like 30-35 pounds per cubic foot _should_ cover both fresh and salt water, so 280# of water at 35 pounds per cubic foot.

If you use something like 1/2 plywood for the bottom with a coating on it, I would want some framing underneath to prevent the bottom from sagging. I agree with Gary R you are going to need some support under the water if you want the bottom of your pool to be flat. Could be a concrete floor, that would solve a lot of problems.

[Stan Calow]

Its actually about 62.4 lbs/cuft.

[Malcolm McLeod]

... so 280# of water at 35 pounds per cubic foot. ...

I believe at room temperatures you'll find fresh water is ~8.33 lbs/gal and (roughly) ~8 gal/cuft, or from look-up =62.4 lbs/cuft. Brine runs more like 10lbs/gal, but greatly depends on % salinity. >>> I'd allow for at least 500 lbs total weight, just of the water.

Support(s) would need to carry this water, add the frame/container and the object(s) to be displayed, and multiply by some factor of safety. The latter would depend on how much deflection you can stand in the tray, cost of a 'crash', who and how many people are leaning/bumping on it, how many toes are under it, display height, floor or table support, etc. (For a public display, I might go with a factor of safety of 3.0X?? ...I've seen those publics in operation.)

And if you've been following the "Joist" thread, please make allowances in the support structure for someone to drink the water and replace it with liquid mercury (SG=~13.6).

[Gary Ragatz]

At 4x8x0.25 feet I come up with I come up with 8 cubic feet of water. I haven't been scuba diving for a long time but I think something like 30-35 pounds per cubic foot _should_ cover both fresh and salt water, so 280# of water at 35 pounds per cubic foot.

Oops - brain cramp! I divided by 144 instead of 1728 (thinking board-feet rather than cubic feet).

[George Yetka]

that .433 is PSI per foot of head. So it should be limited pressure pushing outwards on the side walls. You will still have the weight of water 62.5# x 4'x8'x.25'= 500lbs