Crazy question #1 - building the rectangle

[Alisonvalley]

Help! analysis paralysis! I miss my old pond so much, I’m ready to build a bigger, better pond at our new house in town. Exactly how to do that has been driving me crazy. So thought I’d join your forum and drive ya’ll crazy too. I am aiming for:
- 12’ x 5’ retaining wall, about 20” high. Deep end about 36” so dig out. Shallow end about 16”so fill in. Net capacity 700 – 800 gallons.
- mostly goldfish and waterlilies. Eventually a koi or 2, but not trying for show quality or huge specimens.
- regular black epdm liner, underlayment; waterfall filter, submersible pump.
- our dogs will have access to the pond. Will train them to stay out of the deep end, but will let them romp in the shallow end. That can be another thread.
- zone 6b – cold snaps in the single digits, hot spells around 100F.
- soil is mix of clay and loam, and chock full of shale-y rock.
- area gets full sun until mid-afternoon.

- Pictures: our lot is 50’ wide. The gentleman who built the house 75 years ago constructed an even slope across the whole 50’, keeping the house and garage on a level about 5 or 6 foot higher than the back yard. There is a brick wall and steps on both sides, but we usually scramble down the middle. Sketch shows pond sited near base of current slope, with a retaining wall on one side and a viewing deck on the other. I’ll ‘gentle’ the slope, extending it down to wrap around the back of the pond, planting it with native grasses and flowers. I’ll allow for drainage above and below, keeping run-off out of the pond.

Crazy question #1 – what to make the rectangle out of. We’re narrowing in on Eagle Bay “Highland Stone Free Standing Wall block”, 9” wide, with a 13” bullnose capstone. It doesn’t have the lip on the back like a retaining wall block. It doesn’t have holes for concrete and rebar like cinderblock does.
- will the blocks be strong enough just glued together? (I thought about dry stack concrete block, but then I'd have to make the outside look pretty. I'd rather use wall block that is attractive from the start. Took weeks to reach that conclusion...!)
- right angles can be weak, straight sides can be problems when ponds ice over. Should I use clay/mud or ? to smooth out the backside of the block wall, and round out the corners?
- I’ve read and like the idea of using rigid pink foamboard on the sides for a little extra insulation. Whatever mix I use for smoothing out the corners, could I use a little more and end up with the foamboard at a slight outward angle, instead of absolutely straight up and down?
- would any of that add to the strength of the wall, or make it worse?
- one full wall of the pond rectangle will be buried in the slope, never to be seen. Do I buy enough fancy block to build it same as other 3 sides, or can I use cinder block for the 4th wall? It’s not the same dimension so I can’t picture how to weave it in.

More crazy questions to follow, after this one digests a while. Thanks in advance!

 

[Waterbug]

Those aren't crazy questions at all...very good questions.

- will the blocks be strong enough just glued together? (I thought about dry stack concrete block, but then I'd have to make the outside look pretty. I'd rather use wall block that is attractive from the start. Took weeks to reach that conclusion...!)

I've seen this type of block used in temp ponds at retail places, they do/can hold water at least some period of time. No way to predict how long. 1 month? 100 years? The fun of being a trail blazer.

You should contact the manufacturer. It's free and better than asking yahoos on the internet. Manufacturer says 4' height for soil which is impressive. But that's probably for something like 35-40 lbs/cu ft and water is a bit over 60. The manufacturer likely has the max height calculation for water. At least find out how many lbs/cu ft were used for that 4', that they should have for sure, and then you can guess better.

- right angles can be weak, straight sides can be problems when ponds ice over.

Straight side for this type system and height you're going is probably OK.

Big bingo on the corners. Most stress is there and I don't think (don't know for sure) these type systems (interlocking dry stack) are designed for right angles at all. I'd have high doubts...but I've never even seen this exact product.

I don't see why ice in the pond would have any effect. Foundation is another matter, but that's always the case.

Should I use clay/mud or ? to smooth out the backside of the block wall, and round out the corners?

Sure, that'll work...assuming you mean sloped, not just smeared onto the back like stucco. If good clay it will work very well if you stop rain from getting between the liner and block.

- I’ve read and like the idea of using rigid pink foamboard on the sides for a little extra insulation. Whatever mix I use for smoothing out the corners, could I use a little more and end up with the foamboard at a slight outward angle, instead of absolutely straight up and down?
- would any of that add to the strength of the wall, or make it worse?

Wouldn't add any meaningful strength. Certainly possible it could cause a problem by focusing stress..

- one full wall of the pond rectangle will be buried in the slope, never to be seen. Do I buy enough fancy block to build it same as other 3 sides, or can I use cinder block for the 4th wall? It’s not the same dimension so I can’t picture how to weave it in.

Yes...dry stacked bond beam block, horizontal rebar and concrete filled.

Overall...There are a lot of ways this type of system could go south. Corners would scare me off it. How long it lasts would be a concern.

Options...
I assume you know about split face block. Regular concrete block but one face is made the same way as what you're looking at. Getting them can be difficult, have to go to a mason supplier. And never seen them in bond beam so lot of cutting to make regular into bond beam. Seen people do this...crazy messy, unhealthy.

You could consider a contemporary look like you have in your drawing. Use regular grey bond beam block but instead of the normal running bond you can use a horizontal stack like in your drawing or even a vertical stack. You can do those when using bond beam, rebar and concrete filled. For the vertical stack you can use regular block.

For a natural look I like to use block and then face with real rock. I don't care for the fake stick on stone, and natural stone is almost always way cheaper. Not as hard to apply as it might seem, but time consuming.

Here's a block wall faced with river rock.

And on the left side of this pic is a block pond with a 2" crushed limestone. Super cheap but took a long time.

Sorry I don't have a "for sure" answer for you.

 

[MoonShadows]

Personally, I would not rely on wall blocks, especially without a lip, just glued together with all the weight and force of that water behind them, not to mention what mother nature might throw your way. If you are married to retaining wall block, you should look for a block that has a lip and hollows where you could put extra support strength in.

I really don't think you need the foam insulation board imo.

 

[addy1]

With the size of pond you are thinking of building stay away from koi, they get big and need a lot of water room. Shubunkins make great pond fish real colorful.

My yard is a serious slope around 20-25%, I measured the slope until I found the flattest spot to use. I used a 8 foot +/- high dirt berm on the down hill side to make a level spot for the pond and dug down the top side of the slope 3-4 feet. The dirt berm made a great planting area. But it does take up more yard room, more natural looking since it is a dirt wall. With my slope it would have been tough to make a wall strong enough to handle a pond.

Walled ponds also look great. Great for sitting on to watch the fish. A lot of members have made great walled ponds look at the construction thread for ideas.

 

[Alisonvalley]

Thanks for the input! Addy1, yes I'll stay away from koi at least for a year or two. My husband likes them, but maybe I can talk him into colorful shubunkins instead. Myself, I like fishy-looking goldfish -- nothing fancy. MoonShadows -- I very much like the 2 heights, 3 lengths of the Highland Free standing. There is a similar one with lips but no hollow. To get lips AND hollows, I'd loose the multi-sized effect. So, not sure. Waterbug -- good idea to ask the manufacturer's advice. I'm not expecting to hear them guarantee even a 2 foot wall in a pond application. So I'm thinking alternatives. Including, building a 4-sided 'interior' rectangle of drystack cinderblocks, faced with a 'fancy' wall on the three sides that would show. Or, as you suggest, a veneer of some sort on the cinderblocks. Is a 6 inch block strong enough for a 2 foot wall? Will post more when I hear from the manufacturer .... thanks again!

 

[Waterbug]

6" block is perfectly fine for 2' provided you use bond beam block with horizontal rebar and concrete filled. Top course can be filled an inch or two from the top. After the pond is filled the liner can be cut so it fits inside the block and then cap over that. Rebar in the corners has to be bent (easy for 3/8" rebar). Laying straight pieces and ties in the corner isn't good enough. You can do some vertical rebar every 2 or 3 feet too...not really needed but good insurance. Rebar must be covered by at least 1.5" of concrete on all sides (block counts) to reduce rust issues. Fo sure you don't want to pound the vertical rebar into the ground.

That will hold water long term and works fine if you build a "fancy" wall around the block wall for looks. However if you mortar a veneer you really want to build to make sure the wall doesn't move and crack the veneer. Some veneers hide cracks better than others. Stucco isn't one of those. For a very stable structure you need a proper footing for your climate. Building department can tell you your local frost line. You can use regular 8" block for the footer and below grade foundation and 6" block on top with vertical rebar to tie them together. This can also give you a 2" lip on the inside for mortaring rock over the liner to hide. Mortar doesn't stick to liner so no issue with the rock pulling on the liner. I prefer whole pond to be rock but that's me. I like a clear and clean pond and wrinkles just don't work for me.

Koi...be careful of the internet...opinions are free and worth every penny. Here is a video by Andy Moo that I have shared many times. People who keep Koi and are serious know that pond size isn't really related to whether Koi can be kept or not. It's only in the Water Garden world where arbitrary myths are generated. Pump has to turn over the pond size once, twice, etc... an hour. Plants must cover the surface by 50,75,85%. This type of thinking is endless, completely made up. Don't be talked out of the pond you want too easily. I see it happen a lot and is a big reason why this hobby hasn't grown very much.

Andy is talking about having lots of Koi and growing to max size. In your case I assume you'd be OK if they don't reach max size. Thousands of rather small ponds have Koi and are fine. Andy feeds his Koi with an auto feeder to grow them. Most water garden people feed them maybe max once a day. They don't get real big with less food so maybe get into the 16-24" range. And if you keep the numbers down, test for ammonia once in a awhile you'll probably be fine. Don't worry about the pond size. Lots of small ponds have Koi and are fine. Lots of big ponds have Koi and are not fine. It's not the size that's the determining factor.

 

[Jimmy Gibson]

Here is what I did..... Got the block from Home Depot ( not cheap)... Drove rebar down two foot and filled webs with quickcrete..... Also I knocked the lip off them so I could have a vertical wall

 

[Waterbug]

Rebar driven 2' into soil?

 

[Jimmy Gibson]

Rebar driven 2' into soil?

Yep..... And there is one layer of block that is below ground level all the way around the pond, and each web has a 3/8" rebar in it and filled with quickcrete..... I may be struggling on how to operate a pond.... And keep fish alive but that wall is not going anywhere.....lol..... Also have not lost a fish yet and they seem to be thriving..... I have the filtration /biological tools for the fish I have.... And more but I made the "Newbie" mistake of putting in too many too fast .... But I will get by it..... Thanks to the info on this forum.....Jimmy

 

[Waterbug]

Yeah, it will hold just fine for many years.

For others who research by reading here I would like to point out a possible longer term problem in certain conditions. Building code always requires rebar to be completely encased in concrete, 1.5" of concrete I think. This is required to reduce risk of rust. Rebar in soil will rust and that rust will travel up and into the concrete. Rust expands which fractures the concrete allowing more rust. This can take many years, more years than most ponds are kept, but in some cases can happen in just a few years. And since pounding rebar doesn't help structurally the risk, and added cost, might not be a choice for everyone.

Also more standard to keep the top of vertical rebar down 1.5" from the top.

This isn't to say anyone shouldn't build however they like. Have fun.

 

[CeeJayH]

I built my pong using concrete blocks laid flat so I have a full 9" width to the walls. Absolutely no problems at all. There are photos of the construction and finished pond in my showcase. No rebar used at all,

 

[Waterbug]

Rebar definitely isn't needed...as long as the ground doesn't move too much. Rebar is used mainly to keep things together when ground settles. But ground doesn't always settle. Also the higher the wall the higher the risk.

A person just has to ask themselves how lucky they feel.

 

[sissy]

You have a great pond store up by you in the valley .I love the place it is called springdale water gardens

 

[Jimmy Gibson]

Rebar definitely isn't needed...as long as the ground doesn't move too much. Rebar is used mainly to keep things together when ground settles. But ground doesn't always settle. Also the higher the wall the higher the risk.

A person just has to ask themselves how lucky they feel.

I agree with you to an extent..... For example I built a retaining wall to keep the dirt and mud off my driveway, since I live at the base of a long hill..... I glued it together with a good adhesive .... After a huge rain the whole wall came down..... All the block stayed together the adhesive held..... So when I put it back together used those galvanized strips of metal when you lay brick and drilled a hole in it and drove a 3/8" rebar through it on each block below ground level.... no problem since ..... So in the case of my pond I have a 38" waterline drop from the base of my waterfall to the end of my pond, from past experience I choose to err on the side of caution..... I realize the rebar will not last forever.... And since I am 63 years old, neither will I..... When I go to meet my maker it will be someone's else problem..... Lol Jimmy

 

[Waterbug]

I'm 60. Figure I can make pond walls out of paper towel tubes and probably be OK.

Seriously though, more than a few times I've just dry stacked block, once bales of straw, and I've used billboard plastic and thin hardware store plastic as liner for a temp pond. I agree, build for what you need. But, imo, people researching should be given the limitations and standard methods so they can choose.