water feature on top of a wall

[Melange]

Hi, I need some advice.

I want to build a retaining curved garden wall. 27' long, hight to be

4'1/2' down to 1/2' high and have a square channel on top of it that carries the water from one end of the wall to the other.

If the wall was just one level - ie all 4'1/2 high that would be simple, but as it slops downwards and curves, I'm not sure what to build the wall from.

the options I can think of are:- Block work and render which I've never done before. I could make the shape of the wall from thin plywood and concrete in, I have done a simpler/small project like this. I could combine both options as I don't fancy mixing that much concrete as we have to move all products by hand to the back of the house.

for the top of the wall I was going to use 3 blocks of thermalite type bricks to form the channel shape and render/seal them with something like flexcrete.

Plumbing side, tank, drainage, water flow is all tested (used guttering) and working as expected.

Some constructive comments/advice would be great on how to move forward with the wall :)

Ta Dorine

[meow2222]

If you really have to carry all supplies thru by hand, I dont see any magic solution to that. A retaining wall needs to be a certain size (I presume 9" for 4.5') so thats how much stuff you'll need to carry thru. At 27' long thats a sod of a lot of masonry.

Water laeks could wreck the wall through freeze thaw cycles, so I'd be more thorough about avoiding leaks. You could maybe put a layer or 2 of dpc into the top of the wall for example, and maybe ss eml below it to minimise damage if the wall cracks.

I dont suppose you'll find too many people who've built an aquaduct on here!

NT

[1501]

[Rod]

It's a dump. :-)

But:

would be impressive in *any* garden. Large (very) image link from there is extremely fine.

[Melange]

yes an aquaduct is a good analogy - as for leaks, it wont be on all the time and as the wall slope there wont be any water sitting on it, unless the pump is turned on. I found a product called flexcrete - a cementouse coating, supposed to water proof damp basements and im told was used to waterproof a wall that had water cascading down it so should work fine, this is not an exact science :)

however what i need help with is, in deciding is "How" to build the wall taking all the factors i mentioned into account.

[1501]

Consider lining the trough with GRP.

[Bruce]

I would suggest building the wall in concrete blockwork, remembering to allow proper drainage for the ground that it retains. You will need a properly designed wall with a concrete footing. You will also need to provide expansion/contraction joints in such a long wall.

Then at the top, I would suggest casting the very top section using in-situ concrete formed in plywood shuttering and incorporating a U-shaped channel made from either vitrified clay or uPVC. It would be wise to include an admixture in the concrete that would improve its watertightness. Or you could try one of Flexcrete's epoxy/cement products - but that doesn't sound cheap.

[Adam Aglionby]

Getting a puddle and leak free run over 27` is quite tricky.

Take into account flex in the wall as it settles over its length, it will weigh quite a bit. So something very flexible and UV resistant is required, not sure that tanking is ideal for continuous immersion. Would be tempted to line the channel in butyl and tile the edges in , even render over the tiles if it dosen`t suit the look. If you realy want to use cement, Bondaglass G4 is the evil to use concrete pond sealer, its moisture curing don`t spray it...

Adam

[Melange]

I was considering doing that, many years ago i built a shorter aquaduct style channal, except it was just on the ground and tiled, it never leaked to my knowledge. We added a product to the cement to make it waterproof, cant remember what it was called though, whats yours called?

[Bruce]

There are loads of them.

Just Google on "waterproof concrete admixture"

[The Natural Philosopher]

I didn't put water in mine, or slope it, but I did build it out of concrete blocks. TIE EVERY BLOCK TOGETHER WITH A 'BOW TIE'

Mine got a brick facing, but render is OK I guess.

Why noy use simply three rows of blocks, with the top middle one 'missing' for the channel?

[nightjar]

Hire a concrete pump and have it delivered, pre-mixed, by lorry.

Create it with shuttering and paint the inside of the concrete channel with a pond sealing paint.

Colin Bignell

[Bruce]

Oh don't be silly. It will probably take more concrete to fill the pipeline than is needed for the top of the wall.

[nightjar]

I was addressing the problem of building the whole wall from concrete.

Colin Bignell

[Bruce]

OK, my apologies.

[Melange]

Would that work over a 45m stretch? Which is the distance between front and back garden where the wall is.

How much concrete would I need for a 27' wall high of 4'1/2" for 18' then sloping down from 4'1/2"to 1' high for 9' ?

Would I need a different concrete mix to get a smooth finish once the the ply was removed so no rendering was needed?

[Bruce]

Depends on the thickness. You can work it out yourself, length times average height times thickness. Work it out in metres and fractions of a metre, and the answer is the number of cubic metres you need. Allow 10% to 15% for wastage, plus the volume of concrete in the pipe if you use a pump. Pump line is 100mm bore.

No, just use a better quality plywood and vibrate the concrete evenly and thoroughly for a fair faced finish. Any small remaining air holes can be filled after you strike the shuttering.

In preliminary costing, allow for something like A193 steel mesh reinforcement in the wall, located in the centre. You should not need to reinforce the base slab. You should also provide one expansion joint in the middle of the wall and two contraction joints at the quarter points, otherwise the wall will crack and possibly distort. The need for an expansion joint would mean casting the wall in two halves on different days, with a suitable compressible joint filler being placed against the end of the completed first pour and the second pour cast against it. It would be advisable to cast in some smooth steel locating dowels to keep the two pours aligned, one half of each dowel to be uncoated and cast into the first pour, the other half thickly and evenly coated with bitumen and cast into the second pour.

CAVEAT: The above information is given for rough pricing purposes only, and does not constitute a design. The wall should be designed and detailed by a chartered or incorporated structural or civil engineer or technician, who carries professional liability insurance.

[Melange]

Ok....... that sounds complicated!

I must admit in my mind it went like this: Make foundation, put re-bars in it, make wall shape from ply, pour concrete into said shape, wait 24hours, remove ply and hey there stands a wall, I never for one instant tought a structural engineer would be needed >.< just as well I asked :)

So I guess it might have to be blocks after all ...........