The Brew Cabin

Posted: **Tue Aug 23, 2005 3:51 pm**

Hello Tony-

Hope you are well. Seems I have a hardscape question with every other garden I design. Surely one day I'll have enough experience and I'll stop bothering you. But for now...

I am designing a raised, circular water feature for a tiny town garden. 1100 would be the maximum diameter, with a height of 500mm above ground and another 100 below ground (fish need a warm place in those winter months).

I originally envisioned building the circular wall in brick, knowing that there are special radial bricks available. Alas, a web search shows that the manufacturers only make them for a radius of 450 (=900 diam -- a bit too small) or 675 (=1350 diam. -- too big). Further, when I actually drew it to scale on paper, I realized that the proportion of water surface was way too small for the wall (225 thick) plus its stone coping with a 20mm overhang. Almost as much wall as water on the horizontal surface! Not so attractive.

Okay, what about a radial stretcher, a single skin? Would it be strong enough to withstand the water pressure? But, still I am limited to the manufacturers smallest size (450 radius), which makes a 900 diam pond.

The best proportion would be an 1100 diam pond, using a wall with a width of 100 mm, then a coping of 140 to 150 width on top. That would leave plenty of water surface showing on top.

Aha! I thought. What about rendered concrete??

Can I make a concrete wall as thin as 100mm? Using reinforcing mesh? Bending the shuttering to such small a circle might be difficult... The whole thing would be 600 height, with 100 below ground.

Have I designed something unbuildable?? (Sigh: I am more confident with plants.) I am open to your suggestions.

Thanks.
--Ladysmantle

Posted: **Tue Aug 23, 2005 6:20 pm**

Hope you clients are paying you well for the 'professional' design service!
Always easy to draw it on paper, bit different when it comes to the reality. A large part of garden design should be an understanding of how things are to be built on site.
Could try a concrete manhole ring section - very all in on piece, but very heavy, then render it or maybe timber clad it like a hot tub.
Could be done in brick, but a lot of cutting involved to get round a tight radius, plus a single skin is not very strong. Not just the water pressure to worry about,but in winter the ice will expand and easily break a wall structure. Good luck.

Posted: **Wed Aug 24, 2005 2:30 pm**

OUCH. Hey, everyone has to start somewhere. I am charging appropriately for my experience, and my clients are well aware that I'm a beginner in the hardscape area.

Good idea, the concrete manhole chamber would fit the bill -- but you're right, very heavy, the one that's the right size is almost 600 lbs., from Hepworth Concrete.

Still wondering if I can pour it...

Posted: **Wed Aug 24, 2005 9:01 pm**

I'd side with Ability and use a 1050 dia MH section. Even paying for a 3T mini-digger or a JCB to crane it into place would still be cheaper, and helluva lot quicker than cast in-situ.

However, if you did want to go down the c-i-s route, the formwork for such a relatively small 'circle' would be a work of art. I'd be very, very tempted to use an octagon or decagon for the internal face, and then possibly use manhole shutters for the external face. Failing that, the external face would have to be shuttered using flexi-ply or flexi-mdf.

100mm is the absolute minimum width you could cast, as you need at least 50mm cover for the steel reinforcement (which could be summat like a single sheet of B252, cut and bent on site). You would need a vib poker, of course, and absolute faith inb your formwork skills. although the volume of concrete required is actually quite minimal (around a quarter of a cube for the walls) it's worth considering bringing in readymix just so you can be sure you're getting a quality mix. If you can be sure your site mixer is capable of producing a consistent, high quality mix, then that would be ok, but if you have any doubts at all, go the readymix route.

Posted: **Fri Aug 26, 2005 12:28 pm**

Thank you, guys, for the assistance. Much appreciated!

--ladysmantle

The Brew Cabin

Circular wall: concrete? - How thin can it be?