&#;RECTILINEAR&#; he said. &#;Maybe you haven&#;t noticed but the basic premise of a welded mesh gabion wall is that it&#;s made from rectilinear components&#;.
&#;Yes, but what if they were all curved?&#;, I persisted. &#;Wouldn&#;t that look amazing? All those chunky textures but in lovely circles and sinuous curves&#;..?&#;
&#;You could chine gabion mesh cages to make a really big curve but that wouldn&#;t work for the small radius you want&#;..&#;
At this point my husband sighed the sort of sigh that only the husband of a visionary but mad gardener could sigh. It&#;s the sort of sigh that says:
&#;I do not understand why you feel it necessary to put me through what I know will be months of work and trial and error but I can see that there&#;s no point in either saying no, or complaining about it. It will be done&#;
Unfortunately for my husband, he&#;s an intelligent, resourceful and very practical man, which means he&#;s the perfect candidate to be tormented with such projects.
And so it began.
The garden design
The original garden design layout had been done by my friend Steve Warner of Outhouse Design. Unable to make decisions in my own garden, I sensibly turn to a professional to advise me, and Steve&#;s design featured a circular low retaining wall surrounding our established claret ash leading into a wonderful snake-like curve in front of the deck and then on to another circular paved area beyond. This distracts the eye from the existing competing straight lines of timber deck, pool and fence, none of which are parallel, making a confused jumble of shapes. As we look down on the back garden, a design that works well when viewed from above was paramount. This is something Steve is really good at &#; taking the constraints of a a disordered garden and creating order and pleasing shapes without regimentation or formality where none is wanted.
He&#;d suggested the wall, approximately 400-500mm (15-20&#;)** high and not retaining much could be a dry stone wall, knowing we had a lot of site stone. Then I had the whole gabion wall epiphany.
The wall design
The wall not only curves in a circle, and then elegantly reverse curves, but it also drops over 500mm (20&#;) along its length as the ground falls towards the lower circle. We couldn&#;t bury a lower level of gabion cages as the tree&#;s roots cover the whole area. The whole backyard is over sandstone floaters, so it&#;s not got a lot of soil in which to grow and it was really important that we didn&#;t damage any major anchoring or feeding roots. OK, let&#;s ratchet up the difficulty level another notch!
To keep the wall at a roughly even height, it steps down 7 times along its nearly 9 metre length, each of those step-downs only one gabion mesh square, except for the paver-topped seating area which steps down two squares to accommodate the extra thickness of the pavers. The wall is 320mm (12½&#;) thick to give it enough weight and solidity for a low retaining wall while maximising the size of the enclosed garden bed.
The wall also has a small curved offshoot to tie the retained section back under the deck and there&#;s a small 2 metre (6ft 6&#;) long freestanding &#;echo&#; wall on the other side of the garden that blends into a low rendered wall for a colour and texture contrast.
Materials
Having looked online for what materials we could use, we went back to our (by now) friends Matt and at Ally at Permathene P/L to buy sheets of galvanised 75mm (3 inch) square gabion mesh from which to fashion our own curved gabion baskets. The mesh is made from 4mm (5/32 inch) wire &#; any less and it won&#;t hold its shape well enough.
We bought:
3 sheets of mm long x mm wide (= 6ft 6in x 40&#;)
22 sheets of mm long x 500mm wide (actually mm) (= 6ft 6&#; x 20&#;)
15 brace/support rods (with hooks at each end)
25m roll x 1m wide woven weed mat (= 82ft x 40&#;)
300 galfan C clips
20kg bags 10mm blue metal (stabilising aggregate)
500mm (20&#;) wide tree root barrier
Cold galvit paint
Reinforcing rod for a &#;deadman&#; and as anchor pins
Equipment
spade
bolt cutters
tape measure
level
stringline + metal rod as a central peg
wire twisting fencing tool
large pliers
C-clip tool (a pneumatic tool we hired from Permathene)
a car&#;s spare wheel
Basket design
The circle around the tree has a succession of mm long (80 inch) panels forming the outside perimeter of the wall, matched by necessarily shorter length panels (approximately mm = 65 inch) for the smaller radius inner curve of the back of that wall. Each of theses main sections is internally divided into thirds (every 9 squares or approximately 675mm = 26&#;) with a dividing panel on the radius. Because I wanted a continuous layer of rocks spread along the top, these internal dividers are cut one square lower than the 2 main end panels of each main section so a layer of rocks can cover them.
A further cross brace within each of these 600mm (24&#;) internal sections positioned about halfway up the wall&#;s height helps keep the curved side panels from bulging beyond their correct radius when filled with rocks. NOTE: this means there is a cross brace or divider about every 300mm (12&#;) along the length of the wall. Any further apart and the wall might bulge between supports.
There is no welded mesh with a natural radius. I have seen an installation where a bespoke base was welded and galvanised in a part circular shape to order but this is very expensive and so the bottom of the basket had to be made from sections of rectilinear mesh. We cut sections of mesh in a shape that generally followed the curved footprint of each section but they are cut a little bigger so that there&#;s plenty of attachment points for the long curved side panels. The easiest way to get the right size is to cut them as a &#;top&#; for the two curved walls.
Sometimes the bottom mesh and slide panels aligned so that normal &#;C&#; clips could be used to attach the side to the bottom, but more often the attachment had to be achieved by allowing a protruding piece of wire from the base to be wrapped around the bottom rail of the side panel.
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To make sure the wall won&#;t get pushed over by expanding tree roots, there is also a reinforcing bar &#;deadman&#;, which ties the wall back into the garden behind it, plus two reo-bar &#;pins&#; concreted into the rock below the wall to stop the base of the wall &#;sliding&#; sideways.
Creating the curves
First we marked out the radius of each curve on the plan using a central peg and stringline. If you use a constant radius for each curve, the finished curves will look much better than if you try and do it by eye. But we couldn&#;t find anything online that described how to bend the mesh panels to the right diameter curve so it was trial and error. The first trial was to use straps to wrap a panel around a circular water tank of about the right diameter. After leaving it for a while, the straps were released and bang! the panel snapped straight back to flat. Failure!
At this point Tony realised that we&#;d need to bend the panel beyond the curve we eventually wanted to get the mesh past its elasticity point, and then relax it back until it hit the sweet spot. But how to do all the bending while keeping the curve roughly even along the length of the panel? We needed something that was 1. round (der!) 2. strong enough not to get damaged by the metal mesh 3. not too heavy for us to manage together.
Our first thought was the heavy gas cylinder in the carport. This wasn&#;t bad but we found that the spare wheel from the Subaru wagon was even better as it was a larger diameter. Tony bent the mesh panels around it, by pushing it into the curve while pulling about a 600mm (24&#;) long section at a time. He&#;d then tread the curved panels down to relax them back to the right diameter and hand bend the last few squares to make the curve smoother and more consistent. When we tried to short cut without the pre-bending, we soon discovered that we couldn&#;t rely on the base panels to hold the whole thing in shape. It quickly wanted to &#;unbend&#;. So bend all the panels to the desired end shape first, then assemble.
Assembling the cages
We spread weed mat below the base mesh to prevent any weeds we hadn&#;t yet found and removed from growing up through the wall, as by the time you do see them, they are impossible remove. Where the ground was uneven e.g. over a large tree root we wanted to keep, we added some blue metal aggregate below the bottom mesh panel to create a level base course. In some cases we also cut the mesh panel and shaped it around the larger tree roots where they were higher than our base course. I&#;m sure there will be some of you who think &#;why would would you fuss about that &#; just cut the tree root!&#;&#; but, I can assure you, every major root is important to a tree&#;s stability and health (especially in our shallow, sandy soil), so cut them at your peril!
To cut the base panel pieces we positioned the curved wall panels in place, and then cut a base panel slightly wider than the wall, painting the cut ends with cold galvit.
To hold the separate wall mesh panels together and also to the base, we used a combination of the C-clips we&#;d bought, attached using the pneumatic C-clip tool we&#;d hired, or leaving some of the cut mesh panel ends longer and then looping them around the adjoining mesh panel using the wire twisting tool or large pliers. Although the C-clip tool was fast, it was very difficult to get it into some of the tighter spaces, especially at the base, so we found that the looping method was better in the end.
We also put a dimpled plastic root barrier behind the wall to prevent garden soil from washing into the wall. The gardens drain through to the soil below the wall so we didn&#;t need drainage pipes behind the wall. Finally, we added lengths of electrical conduit through the cages before we filled them so we could add low voltage wall-mounted path lights.
Filling the cages
Having assembled the base and the side walls, tying the base to the side, and then the main cross bracing, it is a simple but VERY laborious matter of filling the cages with cut stone for the desired effect. Each piece needs to bigger than 75mm (3&#;) across one face so it doesn&#;t slip through the mesh. Like the letterbox gabion cages, I filled the internal, unseen sections of the walls with old bricks, broken concrete blocks (from the demolished wall) and rubble, to reuse as many site materials as possible, save on removal costs and keep the good rocks for presentation. I also made small &#;bridges&#; across the tree roots we wanted to save so they didn&#;t get squashed.
As I wanted the faces and top to look closely-tessellated, I used mostly smooth-faced sandstone rather than random or rumbled stone and kept aside pieces that had a right angle, or two, for the edge pieces and top corner stones, as well as sorting them to get a mottling of different colours. The packing took the bulk of the time spent on the whole project. Pieces had to be wedged firmly into place, often by using rubble pushed in behind them to keep them stable. We used sandstone from our own site as we have lots of exposed rock underneath the house and behind our swimming pool in quite a variety of colours. Tony cut out bits of rock and broke it into smaller pieces using a handyman-level electric demolition hammer, which cost us about $350.
Finishing off
We had initially thought the cage would need a top panel but we decided that using standard square or rectangular mesh would not look right. We then contemplated fashioning a single tie wire out of the galvanised wire of the same diameter as the welded mesh. These wires (many of them to replicate the welded mesh) could be set on the curve&#;s radius and both hold the two side panels parallel and add to the look by adding a radial element. But in the end we decided that it would just look too busy, and a good effect was achieved by adding some hidden radial supports just below the top row of filling stone so it was not visible. It still offered sufficient stability but didn&#;t detract from the look of the sandstone from above that we wanted.
We added a sitting section by mortaring on some sandstone pencil-round pavers that had been carefully angle-cut to go around the curve. To do this we finished the packed stone below the top of the cage, spread some geotextile and then concrete on top to bring it up to level. We then mortared on the pavers.
The result
The walls are striking, unique, and beautiful. They are not stable enough for people to walk along or sit on as they disturb the stone pieces, except where we added the paver seating slabs. But they look terrific, and the wonderful contrast between the smooth, sweeping curves and the chunky, tessellated rock is one the most admired parts of our garden.
And yes, I have since found a new challenge for my clever and long-suffering husband &#; to mount a large and very heavy rusting steel &#;wheel&#; sculpture delicately balanced on its narrow edge&#;.without the support being visible!
[** I have converted metric measurements to US equivalents but US-manufactured mesh panels no doubt have slightly different overall lengths and widths.]
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