Best method to render new garden retaining wall?

[windsortg]

I am having a new garden retaining wall built that is going to be about 800mm high. The wall is being made out of concrete blocks and the front facing part of the wall will be rendered.

What is the best way of rendering this wall so that it has a smooth finish and lasts for years? I assume the wall needs to be rendered in layers rather than just one coat of render?

Is there a particular mixture of render that should be applied and once the render has dried, is there a particular paint that should be used?

 

[tony1851]

You need to be wary of rendering retaining walls.

 

[noseall]

You need to be wary of rendering retaining walls.

Agree.

Far too many outdoorsy DIY shows showing a romanticised Mediterranean but false account of beautiful sparkly rendered garden walls. The reality is the UK and especially retaining walls, do not actually behave like that.

 

[windsortg]

@tony1851 - any particular reason why?

 

[noseall]

@tony1851 - any particular reason why?

Retaining walls are notorious for bleeding through corrosive or unsightly deposits, unless the wall is built from thick strong (resistant) materials or is lined on the retaining side. And the other obvious one is the weather. House walls benefit from a decent overhang, but even these become unsightly near the bottom and on the colder/darker elevations. Garden walls have no chance.

 

[freddiemercurystwin]

https://www.diynot.com/diy/threads/...-block-k-rend-and-cavity.544486/#post-4625014

 

[Notch7]

great suggestion -and probably hardly any difference in price to a 2 coat rendered concrete wall

 

[windsortg]

@freddiemercurystwin - many thanks for this. What is the red line denoting on the face of the wall? Also, how important is it for the 15 copper pipes as this will potentially look insightly going across the wall?

You mention 'Render on cement board on vertical treated battens on DPM'. Is that DPM that goes on the face of the wall and then treated battens are screwed through the DRM and into the concrete blocks? What minimum thickness would the battens need to be? Do the cement boards then get attached onto the treated battens?

 

[freddiemercurystwin]

Well note this, to my knowledge, a garden retaining wall has never been built like this but I see no reason why it should fail, it's merely a bit more costly to do is all, it would still need maintenance to keep it looking nice but fundamentally the render board is not getting soaked off and on throughout the year which is why render on just a block wall can fail and/or look horrible in no time.

I daresay you could get the pipe's to exit above the bottom edge of the cement boards so they could be out of sight, they're important to allow any water to discharge. I've seen pipe's through retaining walls that have clearly never had so much as a drip trickle through, but then I've seen others that are permanently damp. You could leave them out, the wall should still work without them, belt and braces really - for the cost of a length of pipe.

I expect you could also reduce the 100mm gap at the bottom too, depending on what's in front of the wall. If it's grass for example and the mower is gonna be bashed into the boards then probably best not, if it was a deck or a stone border then why not, it might get some splash-back but I mentioned earlier it would still need regular maintainance. I think in the other thread I suggested a slither of PVC or similar could be bonded to the base of the block wall, under the cement boards, so it could be wiped down periodically.

Yes, (the red line) is a sheet of DPM on the block wall held in place with the say minimum 25x50wide battens, the cement board fixed to the battens, as ever the devils in the detail.

 

[stuart45]

Great design, mine only failed when the Grandkids painted a wicket on the wall.

 

[windsortg]

thanks @freddiemercurystwin. The wall is being constructed as we speak. A perforated drain pipe has been placed on the back of the wall at the bottom and then there is a membrane running at the back of the blocks (very similar to your dotted blue line in your sketch). The builder has not laid any pipes going through the concrete blocks since this perforated drain pipe should capture any rain water.

The builders are planning on rendering directly onto the concrete blocks and to have a 20-30mm thick tile running along the top. The total length of the wall is approx 20m but has movement joints within the wall at intervals of approx 2m due to the fact I live in an area of clay and have trees nearby. The back of the retaining wall is my lawn (on a slight slope such that the retaining wall is at the bottom of the) slope, and the front of the wall will be against a new, flat porcelain tiled patio.

I am not sure how problematic it will be in introducing cement boards at the front

 

[freddiemercurystwin]

Well if you're just gonna render the blocks then you've been warned, there are literally hundreds of threads on the forum with failed render on retaining walls, even with the membrane behind you've still got a big mass of masonry that will periodically be damp. Speak to your builder, shove this thread under his nose, I daresay he will say he's done hundreds of walls that way and none have ever failed. With a tiled patio at the front I'd be inclined to lose the pipes and just have say a 10mm ventilation gap at the bottom. Just watch the chair legs etc.