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Garden Design

How to build a reused concrete wall

Catherine Stewart

Catherine Stewart

March 4, 2013

We needed some new, low retaining walls in our top garden. “I’ve been thinking“, I said to my husband. This phrase always strikes fear into the heart of my family, though I can’t imagine why. And my idea? Reusing old, broken up concrete to make the new walls. When I first ran the idea past a couple of designer friends they were distinctly luke-warm. “Instead of classy-looking real sandstone? Hmmmm………not sure that will be a look you’ll really want” said one. But I thought I could ‘see’ something beautiful in my mind’s eye.

Incorporating reused concrete steps into the two walls

While excavating behind where the old, nearly-collapsing 2.6m (9ft) high brick retaining wall had been removed, we discovered where some previous owners of our house had chosen to put most of an original driveway, which had been replaced over 30 years before when the now-removed brick retaining wall had been built. Yes, there it was, as fill in the slope, with some pieces about a metre (3ft) square, creating huge voids beneath them. There was just no alternative – all of them would have to come out, or planting and maintaining the slope would be impossible.

Blending the new walls into the rendered driveway kerb

Blending the new reused concrete slab walls into the rendered driveway kerb

The landscape plan (helped along by my garden designer friend Arthur Lathouris – although I’m a designer by trade I find it impossible to design my own garden) called for two new walls, the lower straight and the upper with some gentle curves, but both with an end point that had to blend into the new, rendered concrete kerbing that edged the driveway. Plus we had to figure out a way to incorporate some matching steps up to the top level.

After wall Plan A ‘Sandstone Boulders‘ was rejected on the basis of cost, Plan B ‘Concrete Blocks‘ on ugliness and Plan C ‘Timber Sleepers‘ on longevity, that’s when I had my in-the-middle-of-the-night epiphany. You know, the sort when it’s such a revelation you have to wake your partner and tell them about it right away, even though there is distinctly less enthusiasm for your idea than you think warranted. My new Grand Plan D re-used the old broken concrete, cut up into smaller slabs, to create 500mm (20″) high gravity walls, keeping it on site in a very environmentally-virtuous way. (OK – we’d also already sent tonnes of bricks to landfill and it was costing a bomb). [Note – if you want to build higher walls, or they will have heavy loads nearby (like near a driveway) you should seek engineering advice.]

Reused concrete wall showing smooth-sawn base course

Reused concrete wall showing smooth-sawn base course

Cutting up Adrian's driveway. I think he said we could have it....

Cutting up Adrian’s driveway. I think he said we could have it….

With lots of grunting, heave-ho, sweat and a bent crowbar, we managed to remove all the large concrete slab pieces from inside the slope. There was still considerable suspicion that my Grand Plan D was actually D for delusional, and it soon became apparent that we wouldn’t have nearly enough concrete to do the job. Not sending away concrete to landfill now became begging for other people’s concrete. Driving up the street a few days later, I noticed a neighbour had stacked pieces of sawn concrete from what had once been his driveway, and there were obvious plans to pull up more. A note in the letter box, a very surprised sounding ‘you want what?’ phone call and 5 trailer trips later, we had a base course for our first wall. But still we needed more.

We used some irregularly shaped pieces in the lower courses

We used some irregularly shaped pieces in the lower courses of our reused concrete garden retaining walls

The concrete-for-reuse specifications were: no reinforcing mesh, a standard concrete ‘grey’ with no coloured oxides, and between 70-120mm (2¾”- 5″) thick, which dictated something laid more than 25 years ago. First we found a friend with an old concrete pad, revealed after demolition of his old shed, plus an old path. A hired jackhammer, lots of trailer trips and several aching backs later, we had enough to build the first wall. We developed an insatiable appetite for old concrete paths, particularly those old skinny path/driveway tracks so popular in the 1950s-70s. And each time we asked, the owner would agree (incredulously) and ask “but how are you going to cover up the concrete?”. When we finally bullied my friend Adrian into surrendering his old driveway, we were set.

As I’d never thought of covering it up, this was a bit disconcerting. Was I building something that would be so bug-ugly I’d have to plant densely to disguise it or, worse still, render over the offending broken concrete slabs?

The lower wall is complete

The lower reused concrete retaining wall is complete

Construction was the same as a bookleaf dry stone wall, with the roughly broken 300 x 600mm (1ft x 2ft) concrete slabs laid stretcher-bond style, and the smooth sawn pieces from our neighbour forming the base course, where their textural difference would be less noticeable. Our soil is a very stable clayey sand, only barely removed from concrete itself (it hadn’t moved at all since the wall came down), so we didn’t need to make a strong base course. But in other soils you’d need to excavate a bit further and spread and compact some aggregate first. The base course was angled about 5 degrees backwards into the slope and had the occasional ‘deadman’ – a longer piece of concrete that extended back into the slope – for extra stability. Although 300 x 600mm slabs was the ideal, in reality we had to use up a lot of triangular and oddly-shaped pieces in the lower courses where only their leading face would be seen.

Second reused concrete wall nearly completed

Second reused concrete wall nearly completed

As our acidic, sandy soil sets so hard, to create the level area for the upper wall we hired a small Dingo excavator. While the top wall was being built, I also started improving and planting in the lowest level so we could get some growth happening on our two small trees. As I wanted the wall to ‘weep’, there’s no waterproofing behind it. I also didn’t use any geotextile/fabric behind it, reasoning that the slight backwards angle and the wall’s thickness would be enough to prevent soil washing through, and that’s proven to be correct.

5. Detail of the lower wall

Detail of the lower wall

The tricky part was making up for variations in thickness; concrete from old paths is often only about 50mm (2″) thick but parts of the driveway were up to 130mm (5″). Added to that was the unevenness of many of the pieces, as cheaply poured slabs from several decades ago didn’t tend to have a nice smooth substrate. And some of the concrete had a lot more aggregate making it much darker than other pieces, so there was artistic blending of colours required as well. I was a bit worried that such uneven pieces could make it all look too haphazard, but trial and error and my husband’s skill created a great result. Although he has an engineering background and pretends not to be artistic you can see that’s not really true.

7. Building the curved, second wall, and early planting

Building the curved, second wall, and early planting

An electric rotary hammer drill worked well to chip off the lumps and break up slabs that were too big into more manageable pieces. A fairly dry mix of mortar, concrete chips as packing pieces, trial and error, months of hard slog, a good eye and occasional “why am I doing this again?” finally got both walls built.

The garden starts to fill out

The garden starts to fill out

And the result? Well even my long-suffering husband had to admit that my idea combined with his strength and skill had produced something really attractive, practical and unique. Visitors to the house expressed their admiration (and astonishment) at how good it looked. I hope it’s also more environmentally friendly, as it excluded the manufacture of new materials and prevented old concrete ending up in landfill.

The wide top on the wall also makes convenient access paths through the garden. I do often look at these beautiful walls and wonder whether we could have incorporated some sort of water cascade into the design too. But maybe enough was enough.

Reused concrete slabs to form the garden steps

Reused concrete slabs were used to form the garden steps

 

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Zan
Zan
8 years ago

What a fabulous idea! How much of this stuff is lying around and just looking plain ugly? Recycling has taken on a new meaning. And cost effective? – well even my husband would have to admit that!

helen mck
helen mck
8 years ago

Wow, Catherine, one of those projects that sounds ugly but looks beautiful! And the walls will only get better with time as mosses and lichens grow on them, and plants seed into crevices and spill over!

And I know exactly what you mean about trying to find a use for an initially unwanted resource, then needing more: I’ve been collecting rocks from my neighbour’s paddock to extend my walls, seeing as I’ve run out of supply on my own block!

Richard Laidlaw
8 years ago

“I’ve been thinking” strikes fear into people everywhere :). But it was a good thought – and I enjoyed reading the post.

ecodesign
ecodesign
8 years ago

Catherine, It looks fantastic,

Linda
8 years ago

Great idea beautifully executed Catherine. It could have been a disaster in less artistic hands but you obviously had a vision for how it could work and followed through.

Gella
Gella
8 years ago

No doubt it is artistic and inspirational and a touch Andy Goldsworthy!

Philippa Stewart
Philippa Stewart
8 years ago

A brilliant idea, skillfully and creatively implemented. We have some retaining walls that look remarkably similar to yours – only ours are constructed from expensive sandstone! Quite honestly, with some weathering and those cascading plants to soften the edges, anyone would be hard-pressed to tell the difference. We should nominate you for some kind of eco design award. GardenDrummers should spread the word!

Julie
Julie
8 years ago

Looks fab Cathy. Now I know what to do with all our concrete when and if we ever get around to replacing it with pavers. It’s just the right age too. I’ll second the eco-award nomination!

grim
grim
8 years ago

Ha i have to laugh, at the council i work at i put the same thing around three rose beds but on the vertical, to my eyes they looked great i picked nice looking slabs that most people thought looked great.
As is the norm with most councils if ONE person does not like it you pull it.
So now all of the footpaths that the construction boys pull up go to landfill.
Aren’t CEOs a wonderful lot.

Ros F
Ros F
8 years ago

Looks fantastic. As well as the ecco award nomination, maybe your garden could be included in an Open Gardens event, complete with handout of all your watersaving ideas on show!

Vireya
Vireya
8 years ago

Beautiful result for all that hard work.

Mary
Mary
8 years ago

Looks great! We made a dry wall behind a tank with small rocks strewn all over our acre block! We used a wire cage to hold them in. My only worry is that the holes make a good hiding place for snakes.

Penfellow
Penfellow
8 years ago

Hi Catherine, Thanks, you’ve given me an excellent idea for my raised veg garden!
The old wooden fence posts I’d used to create the veg garden have rotted so I needed to replace them.
I have many cement strips 100x70cm thick and of various broken lengths (previously garden edging) which would be ideal as low walling, probably cemented together. Can’t wait to start the project!
Why didn’t I think of that!

Jenny Matthews
Jenny Matthews
8 years ago

Wow…That looks great! I have some concrete that will need to be ripped up & that looks like such a great use for it. I like the idea of recycling it as it cost so much to get rid of it. And I am sure you know that your husband is not the only man to be fearful of the words ‘I’ve been thinking’.

Judi New
Judi New
8 years ago

Hi Catherine,

Absolutely love it!! As usual, your mind works in mysterious ways and performs wonders (plus Tony’s creative side and muscle).
Also, as usual, I love the way you write about any topic.
Loong time no see!!
Cheers, Judi

Beth
Beth
8 years ago

What a fantastic way to recycle and such an aethetically pleasing result! Inspirational! Thank you for the great story..

Peter Nixon
8 years ago

Been meaning to comment on this one for a while .. Catherine Stewart for Prime Minister !! “Re-use”, the catchword of our time, casts a long shadow across its poorer cousin “recycle” in so many ways but most of all in the saving of ever more carbon to be able to “recycle” … In this case with the exception of that jack hammer, hugely carbon saving none the less by a long, long shot compared with conventional “carbon heavy” means in excavators, new retainer materials & landfill. And that’s before we get near the finished “look”, that of course I’m all for as a designer who wants attention squarely pitched at the PLANTS with hard surface inconspicuously incidental, as it clearly is in this case. Inspired Catherine, trust you to think of ANOTHER way with something so prosaic yet ubiquitous as extraneous concrete. Love your work good friend :)))

Michael W
Michael W
7 years ago

I really enjoyed your creation.And I am looking forward to recycling local concrete for my own project.Thanks for sharing!

Sarah
Sarah
7 years ago

Very beautiful result. Love that it is environmentally friendly

sam
sam
7 years ago

There is a great book (Stanton Library, North Sydney, NSW) that promotes exactly this type of project:

Salvage style : 45 home and garden projects using reclaimed architectural details / Joe Rhatigan with Dana Irwin.
Author: Rhatigan, Joe. — Irwin, Dana.
Published: 2001

Your project has both good aesthetics and environmental credentials.

Nicky
Nicky
7 years ago

Wow – this looks fantastic.
I am mid way through planning out a much smaller project and found your page whilst looking for ideas/inspiration. What started off a a way for me to get rid of/hide a load of broken paving slabs is now turning into some lovely raised beds – well in my head anyway! Cant wait to get started now I have seen how great it can look. Thanks for the inspiration.

Coo
Coo
7 years ago

I’m so inspired : ) Where I live midwest of USA, stones are not readily available. The outrageous estimates for the ugly man made “stones” make my heart sink. I love the limestone look but my budget doesn’t. I do love the idea of recycling and I am now on a MISSION!

Fred
Fred
7 years ago

Thnks catherine. I love the garden. I too was looking to recycle concrete and use for a wall. Your advice is great inspiration.

Timothy Doran
Timothy Doran
6 years ago

This looks great, most especially the bottom photo. We have a concrete driveway that we are about to demolish. We were planning on using sledgehammers, but perhaps we’ll rent a concrete cutter. The best part is, we won’t need to haul all the concrete away — we’ll simply build walls with it. Thank you!

Marada
Marada
6 years ago

So wonderful! I want to create a greenhouse on a hill where the stone wall that holds back the hill is also a foundation wall of the greenhouse. Your article is just perfect, and cost effective and attractive, to boot! Thanks so much for all the great information!!

Virginia
Virginia
6 years ago

A neighbor had a new concrete sidewalk put in and when I looked at the old concrete, I thought raised garden beds. My husband thought I was crazy. I’m going to show him yours. He’ll still think I’m crazy but maybe he’ll be willing to give it a try.

Nikole
Nikole
6 years ago

OMG! I love love love this. I am only missing the key ingredient. No…not the old concrete…the man to lend his strength to my hair-brain re-use ideas.

Steve
Steve
5 years ago

Wow; exactly what I’d like to do too. Does your ground freeze? How did you use the mortar? In the pics the wall looks dry laid.

Brad
Brad
5 years ago

Very Nice , impressive , i am looking at doing the same but with old Kerbing stones turned on their sides.

Gregory Martin
4 years ago

Inspiring! I’m going out back to look at that 1936 concrete in a different way.

Laura Saueracker
4 years ago

Glad to find your post. Thought I might be alone in my crazy idea to use reclaimed concrete. Beautiful garden you have created.

Jillian
Jillian
4 years ago

Hi Catherine, We are in the Upper Blue Mountains, NSW, and have just taken up several old concrete paths, that we would like to give away. We have about 11 square metres of it. Many pieces are still intact rectangular pieces from the paths, and there are lots of irregular broken pieces (also great for crazy-paving). The paths would have been laid in the 1950s, so there’s no reinforcing mesh through it. Do you know anyone who would like to have it? They would have to collect it themselves. There’s about 3 tonnes of it. We are about to post a notice on a community website, but thought we’d ask you first. Many thanks.

Jillian
Jillian
4 years ago

Fantastic – thanks Catherine.

Kaitlyn
4 years ago

What a great way to reuse concrete! It’s awesome these slabs won’t end up in a landfill. The wall and steps add so much appeal!

Florian Wolf
3 years ago

What a great idea, and a gorgeous, quite natural look & feel. Aren’t hubbies willing victims more or less readily succumbing to the crazy ideas of their lovely wives ? Every morning I see such a chap in the mirror, and every time my sweetie has another of her ‘great ideas’ I try to just disappear into thin air….

Her latest idea – which I strongly support – was: let’s move from the city into the bush. So we started looking and came across a large timber yurt with several timber annexes, all in a very dilapidated state & what I now lovingly call our “project home for the not-so-faint-hearted” (aka a complete renovation & refurbishment; one must either be a complete idiot or adventurous & inspired to move there, esp. from a 1st grade island home with all the mod-cons). But: the kids are gone, 21,000 sqm of potential garden is waiting, sandy soil (how do I improve this ?), a river flowing all year behind our block containing endemic rainbow fishes and the occasional platypus, heaps of natives, deadly snakes, a large fire pit with a spit for the occasional wild boar, the remnants of an old cottage garden behind the ruin of the old cottage on the block (doesn’t every proper garden need to have a ruin in it ?), rainwater tanks, no electricity (which will change when we go onto solar), a tractor, a few rusty cars that have been offered to us as “garden ornaments”, and a large concrete terrace that so far I didn’t know what to do with it – but know I know where to get the materials for our Mediterranean dry-stone walls from. Bingo, thank you very much for the great inspiration, Catherine !

Bev Anderson
Bev Anderson
3 years ago

Perfect timing, my coming across your post Catherine. My 10 X 25 foot garage floor built 70 years ago must be removed and everyone insists, dragged to the landfill, which is a very expensive procedure for me and bad for Mother Earth. (Time and minor earthquakes have left it cracked and uneven.) Two sensible contractors have insisted that I forget any crazy idea to salvage the largest pieces of concrete for low retaining walls and garden paths. HA! Now I can refer them to your post, thank you so much Catherine.

Dave Sugar
Dave Sugar
13 days ago

Found this article looking for what to do with a concrete pad I want to remove. How was this cut up? Just a jackhammer? I was planning on using a concrete saw to cut the slab into blocks. But that will give very smooth edges. Could that work and look reasonable when used for a wall?