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#### ReeseC

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I have a concrete and rebar slab in my back yard that I'd like to build a pond on. Unfortunately at 6ft x 7ft x 4ft tall the water weight will be 10,500lbs of pressure.
It doesn't have to be pretty, so I'm considering four walls of concrete and rebar filled cinderblocks masoned together by a contractor. I would line the inside of the box with treated plywood and pond liner. However, I have NO IDEA if this structure would withstand the burst pressure.

Any and all advice would be appreciated.

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pretty sure no one uses cinder blocks anymore,,, blocks are now concrete (concrete masonry unit = cmu ),,, drill holes in the slab, cement in 4' rebar every 18", tie the cmu's together, & fill w/conc,,, no idea why you want to use plywood when redguard's avail,,, pond liner's 19mm & tough enough by itself too,,, 'burst pressure' applies to hydrailics & pressurized things,,, this is any' advise - all to follow :wink2:

#### CaptTom

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Just wondering about the math. My (admittedly limited) understanding of water pressure was that it's based on the depth/height (head) of the water, not the volume. Or did I misunderstand?

#### ReeseC

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Re: Pond walls that can handle 10K pounds of water?

pretty sure no one uses cinder blocks anymore,,, blocks are now concrete (concrete masonry unit = cmu ),,, drill holes in the slab, cement in 4' rebar every 18", tie the cmu's together, & fill w/conc,,, no idea why you want to use plywood when redguard's avail,,, pond liner's 19mm & tough enough by itself too,,, 'burst pressure' applies to hydrailics & pressurized things,,, this is any' advise - all to follow :wink2:
Thank you so much for your time and instruction. In my head the plywood would hold the bulkheads for a pvc intake/outtake, but now that I think about it plumbing is probably installed directly into the cement and sealed.

Just wondering about the math. My (admittedly limited) understanding of water pressure was that it's based on the depth/height (head) of the water, not the volume. Or did I misunderstand?
Thank you for your time. The 10K lbs figure is based solely on the total weight of 1260 gallons of water. I didn't actually know how much of that would be outward strain, shamed to say.

I'm a humble aquarist out of their depth.

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#### ReeseC

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Lol. I haven't been able to find a prefabricated tank that fits my small slab's foot print while being 4 feet deep. It would be fantastic if there was one.

#### Nealtw

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roughly 780gal weighs 6K #,,, 1gal = 231 cu in

#### CaptTom

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Re: Pond walls that can handle 10K pounds of water?

Thank you for your time. The 10K lbs figure is based solely on the total weight of 1260 gallons of water. I didn't actually know how much of that would be outward strain, shamed to say.

I'm a humble aquarist out of their depth.
Well, don't feel bad, I'm out of my depth, too. Was that a pun? Anyway all I know about water pressure is what I learned when I visited a water-powered grist mill as a kid. But luckily, since then, someone invented the internet:

https://www.engineeringtoolbox.com/hydrostatic-pressure-water-d_1632.html

#### MTN REMODEL LLC

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Rough figures..... water exerts about 1/2 pound PSI er foot of depth.....actually less I think around .45 PSI/ft.

4 foot depth of pool will exert less than 2 PSI at the boottom

#### ZTMAN

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I have a concrete and rebar slab in my back yard that I'd like to build a pond on. Unfortunately at 6ft x 7ft x 4ft tall the water weight will be 10,500lbs of pressure.
It doesn't have to be pretty, so I'm considering four walls of concrete and rebar filled cinderblocks masoned together by a contractor. I would line the inside of the box with treated plywood and pond liner. However, I have NO IDEA if this structure would withstand the burst pressure.

Any and all advice would be appreciated.
Have you considered cutting a 6ftx7ft opening in your slab and sinking the pond in the ground?
If you build one of them there ceeeement ponds, Jethro may show up

#### Oso954

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If your slab is 6x7, and you build 4ft walls on top of it, you are not going to have 1,260 gallons of water.

With 8 inch cmu, you need to shrink the 6x7 dimensions by 16 inches. Nor will you fill the water to the 4 ft height. I knocked off 2 inches and came up with 758.3 gal.

So what are you really trying to accomplish here ? Whats the height limit here ?
How much water do you really need?

You can buy a 6 ft diameter plastic rainwater collection tank that’s about 65 inches tall and holds 1,000 gallons. They are about \$550 online not including shipping.

#### ReeseC

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If your slab is 6x7, and you build 4ft walls on top of it, you are not going to have 1,260 gallons of water.

With 8 inch cmu, you need to shrink the 6x7 dimensions by 16 inches. Nor will you fill the water to the 4 ft height. I knocked off 2 inches and came up with 758.3 gal.

So what are you really trying to accomplish here ? Whats the height limit here ?
How much water do you really need?

You can buy a 6 ft diameter plastic rainwater collection tank that’s about 65 inches tall and holds 1,000 gallons. They are about \$550 online not including shipping.
Thank you for your time. The slab is in fact 8' x 9', if that changes anything. You're very right, I didn't factor in outer dimension to the 1K gallon figure, I just slapped the dimensions into a pond calculator figuring the extra wouldn't make a difference in reinforcement, but if that weight difference changes the build needs then I made an error in judgement and I apologize for the confusion.
I'm really only concerned with making a sturdy block structure in the given dimensions.

Tubs unfortunately are not the best option for me for a number of reasons.

Have you considered cutting a 6ftx7ft opening in your slab and sinking the pond in the ground?
If you build one of them there ceeeement ponds, Jethro may show up
Thank you for your time. Digging several feet would be heinous work, as my central Texas back yard is 1 foot of dirt, 1 foot of limestone and several feet of granite. I wrote off the option and built connecting plumbing accordingly.

#### ReeseC

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