[WrenSent]

Hello, I came across this forum looking for info about a project, but I think I need more specific help than I could find. The short version of my question is this: I'm walling in a raised bed with a stock tank pond in the middle, so what is the most cost-effective way of building the wall for someone with very little masonry experience?
The tank's dimensions are 63.25"L x 69"W x 25"H and I need the drain-side of the tank pressed closely to a wall to allow plumbing through it and into an adjoining bog filter; the other sides of the tank will have at least 1 foot of accessible land which will be filled in up to the lip of the tank so the resident turtle can have easy access. I've been doing a lot of research and I feel every time I've made a decision I soon find something else that casts doubt on it. My current plan involves a simple wall of mortared 16x8x8 cinder blocks (CMUs) reinforced with rebar and filled with gravel or cement.

I don't want to pour concrete for the footer (I'll likely need to deconstruct this in a few years), so I was looking into gravel based footers, but it seems that requires a sort of "moving" wall structure which can't happen without breaking the mortar. I've been looking into retaining walls and while the stack-and-lock types of stone might work, they seem much more expensive when considering coverage (it would also complicate running plumbing through the wall.) I don't need something that will last forever but I do need the wall to bear the soil and hold up my weight when I need to clean/maintenance the pond. I live in coastal North Carolina, so frost isn't much of a problem, but water drainage could be especially during the wet seasons (this is why I haven't really considered using lumber.) So is it possible to make this design work with cinder blocks or is there something else I should consider? I would appreciate any help you could give.

 

[Chris616]

Welcome to the forum.

I see that you’ve not keen on the “stack-and-lock” type of prefabricated retaining wall system, but this seems like an ideal application for that. It would do away with the need for mortar and rebar and could be dismantled when necessary. It will also look a lot better, if that is a concern. Both the dry stack retaining wall or a CMU wall would require a well compacted gravel base to build up from.

If you were to use something like this product you could build the wall as I’ve shown in the graphic below, with rounded corners that will look nicer than a 90° corner made from CMUs (will require less material for the wall and fill, also). It wasn’t clear to me if the platform for the bog filters already exists, so I included that in the construction. I didn’t understand the need for a wall between the pond and bog filters, so I omitted that from my sketch. I estimated the total length of my “green” wall to be about 500 inches (42 feet). With the pond wall at 3’ height and the bog filter section at 2’ height the material cost worked out to be about $750. How much were you estimating the CMU wall would cost?

 

[WrenSent]

Welcome to the forum.

I see that you’ve not keen on the “stack-and-lock” type of prefabricated retaining wall system, but this seems like an ideal application for that. It would do away with the need for mortar and rebar and could be dismantled when necessary. It will also look a lot better, if that is a concern. Both the dry stack retaining wall or a CMU wall would require a well compacted gravel base to build up from.

If you were to use something like this product you could build the wall as I’ve shown in the graphic below, with rounded corners that will look nicer than a 90° corner made from CMUs (will require less material for the wall and fill, also). It wasn’t clear to me if the platform for the bog filters already exists, so I included that in the construction. I didn’t understand the need for a wall between the pond and bog filters, so I omitted that from my sketch. I estimated the total length of my “green” wall to be about 500 inches (42 feet). With the pond wall at 3’ height and the bog filter section at 2’ height the material cost worked out to be about $750. How much were you estimating the CMU wall would cost?

View attachment 688896

Thanks for the response! For now, I'm focusing on the wall surrounding the pond; the bog filter is essentially a separate structure and can be supported by cinder blocks without a problem. I'm not concerned with appearance since I'll be covering it with trellises and hanging boxes. All these calculations are from a local Lowe's; I know someone who works there, and can get some discounts, but I haven't accounted for it in the numbers. This is all done rather quickly, so hopefully there aren't major errors in my approximate math here. My product choice is based on price point and suggestions made through research, I'm willing to change them up if there's reason to.
Wall blocks: 103 16"x8"x8" cinder blocks @ $2.41 = $248.23
Rebar (at corners & every 4 feet, cut in half): 5 0.5"x10' Black Steel #4 Rebar @ $6.18 = $30.90
Gravel footing (6"D 16"w so about 22 cu ft): 44 50lb (0.5 cu ft) All-Purpose Gravel @ $4.98 = $219.12
Block Mortar (based on 100 blocks = 3 bags): 4 QUIKRETE ProFinish Blended 80-lb Gray Type S Mortar Mix +
Block Core Fill (10 pieces of rebar, 40 6"x6"x6" holes so about 5 cu ft): 7 plus the initial 4 so 11 @ $6.12 = 67.32
VERY ROUGH TOTAL = $565.57
I've read differing directions on when and how to fill block voids not containing rebar; I'm thinking a sand/gravel mix, but I'll have to keep searching to be sure. Filling them all with a "core fill" would about double the price. Also, I've read you can use #3 rebar, but I don't know for sure. I also based the footing width on "double the block width." This price obviously doesn't include the soil and fill within the walls.
The calculator for your suggested block gives me 374 4"x11.75"x6.75" Pewter Concrete Retaining Wall Blocks @ $1.96 bulk pricing = $733.04. It seems that there can be quite a difference in price between stores, but there's not much to do about it. It's possible there's a brick shop around here that might offer retaining wall blocks cheaper, but I can't tell without calling around first.
Something else I was considering was a combination, such as the wall against the bog filter being cinder blocks and the rest being retaining wall, or maybe the bog wall + the "north" wall being cinder blocks? Not sure if that'd work structurally.

 

[Boogityman]

I don't know anything about walls and have just read this exchange out of learning/interest but are you really balking at a $180 difference on a 40 foot wall project (less if you can use cheaper under your filter) to for some reason avoid use a product that is designed for what you want to do and from what I can tell will be easier to put together and dismantle?

You have already spent that 180 in trying to calculate everything you will need to install the cheaper option, never mind installing it. Diy is great and all but don't put the value of your time at 0, it's the most precious thing we have.

Just my 2 cents.



Sent from my Pixel 5 using Tapatalk

 

[WrenSent]

I don't know anything about walls and have just read this exchange out of learning/interest but are you really balking at a $180 difference on a 40 foot wall project (less if you can use cheaper under your filter) to for some reason avoid use a product that is designed for what you want to do and from what I can tell will be easier to put together and dismantle?

You have already spent that 180 in trying to calculate everything you will need to install the cheaper option, never mind installing it. Diy is great and all but don't put the value of your time at 0, it's the most precious thing we have.

Just my 2 cents.



Sent from my Pixel 5 using Tapatalk

To me, I've more resources in the time & effort department than the financial one, so that's been the focus of my question. If what I've designed can be done, I don't mind the effort and can allocate the money I would've spent on different blocks into other parts of the project that don't involve the wall. If this design can't (or shouldn't) be done, then I will put the necessary resources towards a different design. But this isn't an area I have much understanding in, so what can or can't be done is a somewhat beyond me and so I hope someone with more knowledge can point me in the right direction.