9 Step Gabion Retaining Wall Build with Galfan Mesh and Yorkshire Cobble Over a 5-Metre Run

Why a 1:10 batter changes the dig before you order a single basket

Set the wall back into the slope at a 1:10 batter, meaning 100mm of lean for every metre of height. Over a 1.5m stack that is 150mm of horizontal offset, and it has to be cut into the trench geometry before you order baskets. A vertical gabion face on a clay bank tends to creep forward as the fill settles, and the lean is the cheapest way to buy a safety margin without engineering calculations.

Dig the trench 600mm wide for a 500mm-deep basket, leaving 100mm of working room at the back for the drainage layer. Depth depends on your frost line and bearing soil. On the kind of sloping border that swallows sleepers and topiary alike, a 200mm sub-base of compacted MOT Type 1 under the first course spreads the load and stops differential settlement. A whacker plate over that, two passes minimum, gives you a level platform. Check it with a 1.2m spirit level across the run and along it, because a basket sitting on a high spot will rock and the whole course inherits the error.

The trench spoil is worth keeping. You will backfill the cut behind the wall with it once the drainage is in, and a 5-metre run generates enough clay to do exactly that.

Galfan versus standard galvanised: the coating that decides year ten

Galfan is a zinc-aluminium alloy coating, roughly 95 percent zinc and 5 percent aluminium, applied to the mesh wire to BS EN 10223-3 standards for gabion work. Against the older heavy galvanised finish it gives two to three times the corrosion life in the saturated, slightly acidic conditions you get behind a wall on a wet slope. For a structure you do not intend to rebuild, the price difference at order stage is small against the cost of the cobble and your labour.

Specify mesh aperture at 80mm x 100mm with a 3mm wire diameter for the body and a thicker 3.9mm selvedge wire on the edges. The aperture matters because it sets your minimum fill stone size. Anything that can pass through an 80mm gap will migrate and the basket loses its packed density. Yorkshire cobble graded at 100mm to 200mm sits comfortably above that threshold, which is why it is a standard gabion fill across northern England.

Order lacing wire separately. Most baskets arrive flat-packed with helical spirals for the main joints, but you will want 2.2mm Galfan lacing wire for the internal bracing wires and any field corrections. A 5-metre, three-high wall in 1m units needs fifteen baskets, and the wire to lace them runs to several coils. Buy a roll over your estimate.

Assembling and lacing the first course

Unfold each basket on flat ground and stand the four sides up against the base panel. The lid stays open. Join adjacent panels with the helical spirals, threading top to bottom and crimping both ends with pliers so they cannot unwind. Where two baskets meet along the run, lace the touching faces together as well. A wall laced as a continuous unit behaves far better than a row of independent boxes leaning on each other.

Seat the first course on the sub-base and check the batter line. Run a string from a back-stake set to your 1:10 lean and bring the rear face of each basket to it. Tweak the level with thin slate slips under the wire mesh if a corner sits proud. Only once the entire bottom course is laced, levelled and aligned do you start filling, because a filled basket weighs upward of 1.4 tonnes and will not move for you afterwards.

Packing the cobble so the face stays tight

The visible faces are hand-placed. This is the slow part and the part that separates a wall that looks built from one that looks tipped. Set the larger, flatter Yorkshire cobbles against the mesh with their best face outward, fitting them like dry-stone coursing so the gaps between stones are minimal. Behind that facing layer you can machine-fill or shovel the interior with the same grade, but the outer 150mm earns hand-placing.

At one third and two thirds of the basket height, fit internal bracing wires across the width. These tie the front face to the back and stop the long faces bowing outward under fill pressure. Loop the 2.2mm Galfan wire through the mesh on both faces and twist it tight. Skip these and a 1m-high basket will belly within a season; a Stihl MS 170 chainsaw clearing the bank above will throw enough vibration and root disturbance to find every unbraced face.

Fill in 250mm lifts and tamp each lift by hand with a length of timber. Aim for a packed density that leaves no rattling voids. Overfill each basket by about 25mm above the rim before closing the lid, because the fill consolidates and a flush-filled basket will dish in the middle once the next course loads it. Close the lid and lace it down the full perimeter and across every internal partition.

Drainage behind the wall

A retaining wall fails on water pressure long before it fails on weight. Behind the laced baskets, lay a non-woven geotextile membrane against the mesh to stop fines washing through and clogging the fill. Then backfill the trench gap with 20mm clean angular gravel, not the clay spoil, for at least 300mm of depth across the full height. At the base, bed a 100mm perforated land drain in that gravel, falling at least 1:100 along the run to a daylight outlet or soakaway. This is the single component most often left out, and its absence is why so many garden gabion walls lean within five years.

A worked fill estimate for the 5-metre run

Three courses of 1m x 1m x 0.5m baskets over 5 metres give a gross volume of 5 x 1 x 1.5, which is 7.5 cubic metres. Yorkshire cobble at the supplier sells by weight, and the bulk density of packed 100 to 200mm stone runs around 1.5 tonnes per cubic metre. That puts the order at roughly 11.25 tonnes. Add 10 percent for waste, hand-fitting offcuts and the inevitable underestimate, and you order 12.5 tonnes, delivered in bulk bags or loose tipped if you have access for the lorry.

The gravel drainage layer is a separate calculation. A 300mm-deep, 1.5m-high zone over 5 metres is 5 x 0.3 x 1.5, which is 2.25 cubic metres, near enough 3.4 tonnes of 20mm clean stone. The land drain is 5 metres plus a run to the outfall, so order 8 metres of 100mm perforated pipe and the couplings to suit.

Labour is the hidden line. Hand-facing the visible side of fifteen baskets at a careful pace is the bulk of the work, far more than the lacing or the dig. Two people will spend a full weekend on the facing alone if the cobble is well graded, longer if it arrived as a mixed pile that needs sorting for size before it touches the mesh.

Capping and the finished line

The top course takes a coping. Lace the lids tight and finish with a band of the flattest cobbles set deliberately level, or bed a row of slate slips into the top fill for a cleaner line where the wall meets a wildlife pond edge or a planted border above. Some builders mortar a stone cap onto the top basket for a defined edge, though a well-packed gabble top sheds water perfectly well on its own.

The question the build leaves open is what grows at the foot of it. A south-facing gabion face stores and releases heat, and the gravel pocket behind the top course drains sharply, which suits some planting and starves others. Whether that microclimate earns a row of blueberries in ericaceous compost or a dry-loving alpine edge is the decision that outlives the stonework, and the wall gives you no clue which way to go.